diff --git a/include/xlnt/cell/cell.hpp b/include/xlnt/cell/cell.hpp
index 134faacd..630753d2 100644
--- a/include/xlnt/cell/cell.hpp
+++ b/include/xlnt/cell/cell.hpp
@@ -111,7 +111,9 @@ public:
     bool has_hyperlink() const;
     
     // style
+    bool has_style() const;
     std::size_t get_style_id() const;
+    void set_style_id(std::size_t style_id);
     const number_format &get_number_format() const;
     void set_number_format(const number_format &format);
     const font &get_font() const;
diff --git a/include/xlnt/common/hash_combine.hpp b/include/xlnt/common/hash_combine.hpp
new file mode 100644
index 00000000..882a270a
--- /dev/null
+++ b/include/xlnt/common/hash_combine.hpp
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <functional>
+
+namespace xlnt {
+    
+//TODO: Can this be in source->detail, or must it be in a header?
+template <class T>
+inline void hash_combine(std::size_t& seed, const T& v)
+{
+    std::hash<T> hasher;
+    seed ^= hasher(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
+}
+    
+} // namespace xlnt
\ No newline at end of file
diff --git a/include/xlnt/reader/excel_reader.hpp b/include/xlnt/reader/excel_reader.hpp
index 02769a37..4c46d1e2 100644
--- a/include/xlnt/reader/excel_reader.hpp
+++ b/include/xlnt/reader/excel_reader.hpp
@@ -23,6 +23,7 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <iostream>
 #include <string>
 #include <vector>
 
@@ -30,9 +31,15 @@ namespace xlnt {
     
 class workbook;
 
-std::string CentralDirectorySignature();
-std::string repair_central_directory(const std::string &original);
-workbook load_workbook(const std::string &filename, bool guess_types = false, bool data_only = false);
-workbook load_workbook(const std::vector<std::uint8_t> &bytes, bool guess_types = false, bool data_only = false);
+class excel_reader
+{
+public:
+    static std::string CentralDirectorySignature();
+    static std::string repair_central_directory(const std::string &original);
+
+    static workbook load_workbook(std::istream &stream, bool guess_types = false, bool data_only = false);
+    static workbook load_workbook(const std::string &filename, bool guess_types = false, bool data_only = false);
+    static workbook load_workbook(const std::vector<std::uint8_t> &bytes, bool guess_types = false, bool data_only = false);
+};
 
 } // namespace xlnt
diff --git a/include/xlnt/reader/shared_strings_reader.hpp b/include/xlnt/reader/shared_strings_reader.hpp
index 01933814..0c575c75 100644
--- a/include/xlnt/reader/shared_strings_reader.hpp
+++ b/include/xlnt/reader/shared_strings_reader.hpp
@@ -28,9 +28,15 @@
 
 namespace xlnt {
     
-std::vector<std::string> read_shared_strings(const std::string &xml_string);
-void read_string_table(const std::string &xml_source);
-std::string get_string();
-std::string get_text();
-    
+class zip_file;
+
+class shared_strings_reader
+{
+public:
+    std::vector<std::string> read_strings(zip_file &archive);
+    void read_string_table(const std::string &xml_source);
+    std::string get_string();
+    std::string get_text();
+};
+
 } // namespace xlnt
diff --git a/include/xlnt/reader/style_reader.hpp b/include/xlnt/reader/style_reader.hpp
index 034fc6a8..35137951 100644
--- a/include/xlnt/reader/style_reader.hpp
+++ b/include/xlnt/reader/style_reader.hpp
@@ -27,21 +27,60 @@
 #include <unordered_map>
 #include <vector>
 
-#include "style.h"
+#include "xlnt/workbook/workbook.hpp"
+
+namespace pugi {
+class xml_node;
+} // namespace pugi
 
 namespace xlnt {
+
+class border;
+class fill;
+class font;
+class named_style;
+class number_format;
+class style;
+class zip_file;
     
-void read_styles();
-void read_custom_num_formats();
-void read_color_index();
-void read_dxfs();
-void read_fonts();
-void read_fills();
-void read_borders();
-void read_named_styles();
-void read_style_names();
-void read_cell_styles();
-void read_xfs();
-void read_style_table();
+class style_reader
+{
+public:
+    style_reader(workbook &wb);
+    
+    void read_styles(zip_file &archive);
+    
+    const std::vector<style> &get_styles() const { return styles_; }
+    
+    const std::vector<border> &get_borders() const { return borders_; }
+    const std::vector<fill> &get_fills() const { return fills_; }
+    const std::vector<font> &get_fonts() const { return fonts_; }
+    const std::vector<number_format> &get_number_formats() const { return number_formats_; }
+    
+private:
+    style read_style(pugi::xml_node stylesheet_node, pugi::xml_node xf_node);
+    
+    void read_borders(pugi::xml_node borders_node);
+    void read_fills(pugi::xml_node fills_node);
+    void read_fonts(pugi::xml_node fonts_node);
+    void read_number_formats(pugi::xml_node num_fmt_node);
+    
+    void read_color_index();
+    void read_dxfs();
+    void read_named_styles(pugi::xml_node named_styles_node);
+    void read_style_names();
+    void read_cell_styles();
+    void read_xfs();
+    void read_style_table();
+
+    workbook wb_;
+    
+    std::vector<style> styles_;
+    
+    std::vector<border> borders_;
+    std::vector<fill> fills_;
+    std::vector<font> fonts_;
+    std::vector<number_format> number_formats_;
+};
 
 } // namespace xlnt
diff --git a/include/xlnt/reader/worksheet_reader.hpp b/include/xlnt/reader/worksheet_reader.hpp
index 92d3a74b..455e55f3 100644
--- a/include/xlnt/reader/worksheet_reader.hpp
+++ b/include/xlnt/reader/worksheet_reader.hpp
@@ -23,19 +23,16 @@
 // @author: see AUTHORS file
 #pragma once
 
-#include <iostream>
 #include <string>
-#include <unordered_map>
 #include <vector>
 
 namespace xlnt {
     
+class relationship;
 class workbook;
-class worksheet;
+class zip_file;
 
-worksheet read_worksheet(std::istream &handle, workbook &wb, const std::string &title, const std::vector<std::string> &string_table, const std::unordered_map<int, std::string> &custom_number_formats);
-void read_worksheet(worksheet ws, std::istream &stream, const std::vector<std::string> &string_table, const std::vector<int> &number_format_ids, const std::unordered_map<int, std::string> &custom_number_formats);
-void read_worksheet(worksheet ws, const std::string &xml_string, const std::vector<std::string> &string_table, const std::vector<int> &number_format_ids, const std::unordered_map<int, std::string> &custom_number_formats);
+void read_worksheet(worksheet ws, zip_file &archive, const relationship &rel, const std::vector<std::string> &shared_strings);
 std::string read_dimension(const std::string &xml_string);
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/alignment.hpp b/include/xlnt/styles/alignment.hpp
index 6c051959..aff69170 100644
--- a/include/xlnt/styles/alignment.hpp
+++ b/include/xlnt/styles/alignment.hpp
@@ -23,6 +23,8 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <xlnt/common/hash_combine.hpp>
+
 namespace xlnt {
 
 /// <summary>
@@ -33,6 +35,7 @@ class alignment
 public:
     enum class horizontal_alignment
     {
+        none,
         general,
         left,
         right,
@@ -43,27 +46,72 @@ public:
     
     enum class vertical_alignment
     {
+        none,
         bottom,
         top,
         center,
         justify
     };
     
+    bool get_wrap_text() const
+    {
+        return wrap_text_;
+    }
+    
     void set_wrap_text(bool wrap_text)
     {
         wrap_text_ = wrap_text;
     }
     
+    bool has_horizontal() const
+    {
+        return horizontal_ != horizontal_alignment::none;
+    }
+    
+    horizontal_alignment get_horizontal() const
+    {
+        return horizontal_;
+    }
+    
+    void set_horizontal(horizontal_alignment horizontal)
+    {
+        horizontal_ = horizontal;
+    }
+    
+    bool has_vertical() const
+    {
+        return vertical_ != vertical_alignment::none;
+    }
+    
+    vertical_alignment get_vertical() const
+    {
+        return vertical_;
+    }
+    
+    void set_vertical(vertical_alignment vertical)
+    {
+        vertical_ = vertical;
+    }
+    
     bool operator==(const alignment &other) const
     {
         return hash() == other.hash();
     }
     
-    std::size_t hash() const { return 0; }
+    std::size_t hash() const
+    {
+        std::size_t seed = wrap_text_;
+        seed = seed << 1 & shrink_to_fit_;
+        hash_combine(seed, static_cast<std::size_t>(horizontal_));
+        hash_combine(seed, static_cast<std::size_t>(vertical_));
+        hash_combine(seed, text_rotation_);
+        hash_combine(seed, indent_);
+        return seed;
+    }
     
 private:
-    horizontal_alignment horizontal_ = horizontal_alignment::general;
-    vertical_alignment vertical_ = vertical_alignment::bottom;
+    horizontal_alignment horizontal_ = horizontal_alignment::none;
+    vertical_alignment vertical_ = vertical_alignment::none;
     int text_rotation_ = 0;
     bool wrap_text_ = false;
     bool shrink_to_fit_ = false;
diff --git a/include/xlnt/styles/border.hpp b/include/xlnt/styles/border.hpp
index a1837ba5..0ef2320f 100644
--- a/include/xlnt/styles/border.hpp
+++ b/include/xlnt/styles/border.hpp
@@ -24,17 +24,12 @@
 #pragma once
 
 #include <cstddef>
+#include <functional>
 
 #include "side.hpp"
+#include "../common/hash_combine.hpp"
 
 namespace xlnt {
-
-template<typename T>
-struct optional
-{
-    T value;
-    bool initialized;
-};
     
 enum class diagonal_direction
 {
@@ -49,28 +44,52 @@ class border
 public:
     static border default_border();
     
-    optional<side> start;
-    optional<side> end;
-    optional<side> left;
-    optional<side> right;
-    optional<side> top;
-    optional<side> bottom;
-    optional<side> diagonal;
-    optional<side> vertical;
-    optional<side> horizontal;
+    bool start_assigned;
+    side start;
+    bool end_assigned;
+    side end;
+    bool left_assigned;
+    side left;
+    bool right_assigned;
+    side right;
+    bool top_assigned;
+    side top;
+    bool bottom_assigned;
+    side bottom;
+    bool diagonal_assigned;
+    side diagonal;
+    bool vertical_assigned;
+    side vertical;
+    bool horizontal_assigned;
+    side horizontal;
 
-    bool outline;
-    bool diagonal_up;
-    bool diagonal_down;
+    bool outline = false;
+    bool diagonal_up = false;
+    bool diagonal_down = false;
     
-    diagonal_direction diagonal_direction_;
+    diagonal_direction diagonal_direction_ = diagonal_direction::none;
     
     bool operator==(const border &other) const
     {
         return hash() == other.hash();
     }
     
-    std::size_t hash() const { return 0; }
+    std::size_t hash() const
+    {
+        std::size_t seed = 0;
+        
+        if(start_assigned) hash_combine(seed, start.hash());
+        if(end_assigned) hash_combine(seed, end.hash());
+        if(left_assigned) hash_combine(seed, left.hash());
+        if(right_assigned) hash_combine(seed, right.hash());
+        if(top_assigned) hash_combine(seed, top.hash());
+        if(bottom_assigned) hash_combine(seed, bottom.hash());
+        if(diagonal_assigned) hash_combine(seed, diagonal.hash());
+        if(vertical_assigned) hash_combine(seed, vertical.hash());
+        if(horizontal_assigned) hash_combine(seed, horizontal.hash());
+
+        return seed;
+    }
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/color.hpp b/include/xlnt/styles/color.hpp
index 14580aca..60049619 100644
--- a/include/xlnt/styles/color.hpp
+++ b/include/xlnt/styles/color.hpp
@@ -28,6 +28,13 @@ namespace xlnt {
 class color
 {
 public:
+    enum class type
+    {
+        indexed,
+        theme,
+        auto_
+    };
+    
     static const color black;
     static const color white;
     static const color red;
@@ -39,17 +46,74 @@ public:
     static const color yellow;
     static const color darkyellow;
     
-    color(int index) : index_(index)
+    color() {}
+    
+    color(type t, std::size_t v) : type_(t), index_(v)
     {
     }
     
     bool operator==(const color &other) const
     {
+        if(type_ != other.type_) return false;
         return index_ == other.index_;
     }
     
+    void set_auto(int auto_index)
+    {
+        type_ = type::auto_;
+        index_ = auto_index;
+    }
+    
+    void set_index(int index)
+    {
+        type_ = type::indexed;
+        index_ = index;
+    }
+    
+    void set_theme(int theme)
+    {
+        type_ = type::theme;
+        index_ = theme;
+    }
+    
+    type get_type() const
+    {
+        return type_;
+    }
+    
+    int get_auto() const
+    {
+        if(type_ != type::auto_)
+        {
+            throw std::runtime_error("not auto color");
+        }
+        
+        return index_;
+    }
+    
+    int get_index() const
+    {
+        if(type_ != type::indexed)
+        {
+            throw std::runtime_error("not indexed color");
+        }
+        
+        return index_;
+    }
+    
+    int get_theme() const
+    {
+        if(type_ != type::theme)
+        {
+            throw std::runtime_error("not theme color");
+        }
+        
+        return index_;
+    }
+    
 private:
-    int index_;
+    type type_ = type::indexed;
+    int index_ = 0;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/fill.hpp b/include/xlnt/styles/fill.hpp
index 164fa9ca..54c8d17c 100644
--- a/include/xlnt/styles/fill.hpp
+++ b/include/xlnt/styles/fill.hpp
@@ -23,7 +23,8 @@
 // @author: see AUTHORS file
 #pragma once
 
-#include "color.hpp"
+#include "../common/hash_combine.hpp"
+#include "../styles/color.hpp"
 
 namespace xlnt {
 
@@ -34,38 +35,139 @@ public:
     {
         none,
         solid,
-        gradient_linear,
-        gradient_path,
-        pattern_darkdown,
-        pattern_darkgray,
-        pattern_darkgrid,
-        pattern_darkhorizontal,
-        pattern_darktrellis,
-        pattern_darkup,
-        pattern_darkvertical,
-        pattern_gray0625,
-        pattern_gray125,
-        pattern_lightdown,
-        pattern_lightgray,
-        pattern_lightgrid,
-        pattern_lighthorizontal,
-        pattern_lighttrellis,
-        pattern_lightup,
-        pattern_lightvertical,
-        pattern_mediumgray,
+        gradient,
+        pattern
     };
     
-    type type_ = type::none;
-    int rotation = 0;
-    color start_color = color::white;
-    color end_color = color::black;
+    enum class gradient_type
+    {
+        linear,
+        path
+    };
     
-    virtual bool operator==(const fill &other) const
+    enum class pattern_type
+    {
+        none,
+        solid,
+        darkdown,
+        darkgray,
+        darkgrid,
+        darkhorizontal,
+        darktrellis,
+        darkup,
+        darkvertical,
+        gray0625,
+        gray125,
+        lightdown,
+        lightgray,
+        lightgrid,
+        lighthorizontal,
+        lighttrellis,
+        lightup,
+        lightvertical,
+        mediumgray,
+    };
+    
+    type get_type() const { return type_; }
+    void set_type(type t) { type_ = t; }
+    std::string get_pattern_type_string() const
+    {
+        if(type_ != type::pattern)
+        {
+            throw std::runtime_error("not pattern fill");
+        }
+        
+        switch(pattern_type_)
+        {
+            case pattern_type::none: return "none";
+            case pattern_type::solid: return "solid";
+            case pattern_type::darkdown: return "darkdown";
+            case pattern_type::darkgray: return "darkgray";
+            case pattern_type::darkgrid: return "darkgrid";
+            case pattern_type::darkhorizontal: return "darkhorizontal";
+            case pattern_type::darktrellis: return "darktrellis";
+            case pattern_type::darkup: return "darkup";
+            case pattern_type::darkvertical: return "darkvertical";
+            case pattern_type::gray0625: return "gray0625";
+            case pattern_type::gray125: return "gray125";
+            case pattern_type::lightdown: return "lightdown";
+            case pattern_type::lightgray: return "lightgray";
+            case pattern_type::lightgrid: return "lightgrid";
+            case pattern_type::lighthorizontal: return "lighthorizontal";
+            case pattern_type::lighttrellis: return "lighttrellis";
+            case pattern_type::lightup: return "lightup";
+            case pattern_type::lightvertical: return "lightvertical";
+            case pattern_type::mediumgray: return "mediumgray";
+            default: throw std::runtime_error("invalid type");
+        }
+    }
+    pattern_type get_pattern_type() const
+    {
+        return pattern_type_;
+    }
+    void set_pattern_type(pattern_type t) { pattern_type_ = t; }
+    void set_gradient_type(gradient_type t) { gradient_type_ = t; }
+    
+    void set_foreground_color(const color &c)
+    {
+        foreground_color_ = c;
+        foreground_color_assigned_ = true;
+    }
+    
+    void set_background_color(const color &c)
+    {
+        background_color_ = c;
+        background_color_assigned_ = true;
+    }
+    
+    color get_foreground_color() const
+    {
+        return foreground_color_;
+    }
+    
+    color get_background_color() const
+    {
+        return background_color_;
+    }
+    
+    bool has_foreground_color() const
+    {
+        return foreground_color_assigned_;
+    }
+    
+    bool has_background_color() const
+    {
+        return background_color_assigned_;
+    }
+    
+    bool operator==(const fill &other) const
     {
         return hash() == other.hash();
     }
     
-    virtual std::size_t hash() const { return 0; }
+    std::size_t hash() const
+    {
+        auto seed = static_cast<std::size_t>(type_);
+        
+        if(type_ == type::pattern)
+        {
+            hash_combine(seed, static_cast<std::size_t>(pattern_type_));
+        }
+        
+        return seed;
+    }
+    
+private:
+    type type_ = type::none;
+    pattern_type pattern_type_;
+    gradient_type gradient_type_;
+    int rotation_ = 0;
+    bool foreground_color_assigned_ = false;
+    color foreground_color_ = color::black;
+    bool background_color_assigned_ = false;
+    color background_color_ = color::white;
+    color start_color_ = color::white;
+    color end_color_ = color::black;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/font.hpp b/include/xlnt/styles/font.hpp
index 54246fb6..23b613cf 100644
--- a/include/xlnt/styles/font.hpp
+++ b/include/xlnt/styles/font.hpp
@@ -25,6 +25,7 @@
 
 #include <string>
 
+#include <xlnt/common/hash_combine.hpp>
 #include <xlnt/styles/color.hpp>
 
 namespace xlnt {
@@ -44,18 +45,51 @@ public:
     };
     
     void set_bold(bool bold) { bold_ = bold; }
+    bool is_bold() const { return bold_; }
+    
+    void set_size(int size) { size_ = size; }
+    int get_size() const { return size_; }
+    
+    void set_name(const std::string &name) { name_ = name; }
+    std::string get_name() const { return name_; }
+    
+    void set_color(color c) { color_ = c; }
+    void set_family(int family) { has_family_ = true; family_ = family; }
+    void set_scheme(const std::string &scheme) { has_scheme_ = true; scheme_ = scheme; }
+    
+    color get_color() const { return color_; }
+    
+    bool has_family() const { return has_family_; }
+    bool has_scheme() const { return has_scheme_; }
+    
+    std::size_t hash() const
+    {
+        std::size_t seed = bold_;
+        seed = seed << 1 & italic_;
+        seed = seed << 1 & superscript_;
+        seed = seed << 1 & subscript_;
+        seed = seed << 1 & strikethrough_;
+        hash_combine(seed, name_);
+        hash_combine(seed, size_);
+        hash_combine(seed, static_cast<std::size_t>(underline_));
+        hash_combine(seed, static_cast<std::size_t>(color_.get_type()));
+        switch(color_.get_type())
+        {
+            case color::type::indexed: hash_combine(seed, color_.get_index()); break;
+            case color::type::theme: hash_combine(seed, color_.get_theme()); break;
+            default: break;
+        }
+        hash_combine(seed, family_);
+        hash_combine(seed, scheme_);
+        
+        return seed;
+    }
     
     bool operator==(const font &other) const
     {
         return hash() == other.hash();
     }
     
-    int get_size() const { return size_; }
-    std::string get_name() const { return name_; }
-    bool is_bold() const { return bold_; }
-    
-    std::size_t hash() const { return 0; }
-    
 private:
     friend class style;
     
@@ -67,7 +101,11 @@ private:
      bool subscript_ = false;
      underline underline_ = underline::none;
      bool strikethrough_ = false;
-     color color_ = color::black;
+     color color_;
+     bool has_family_ = false;
+     int family_;
+     bool has_scheme_ = false;
+     std::string scheme_;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/gradient_fill.hpp b/include/xlnt/styles/gradient_fill.hpp
deleted file mode 100644
index 39244de1..00000000
--- a/include/xlnt/styles/gradient_fill.hpp
+++ /dev/null
@@ -1,39 +0,0 @@
-// Copyright (c) 2015 Thomas Fussell
-// Copyright (c) 2010-2015 openpyxl
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, WRISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE
-//
-// @license: http://www.opensource.org/licenses/mit-license.php
-// @author: see AUTHORS file
-#pragma once
-
-#include "fill.hpp"
-
-namespace xlnt {
-
-class gradient_fill : public fill
-{
-public:
-    std::size_t hash() const override { return 0; }
-    
-private:
-    
-};
-
-} // namespace xlnt
diff --git a/include/xlnt/styles/named_style.hpp b/include/xlnt/styles/named_style.hpp
index a218bd55..56e0da11 100644
--- a/include/xlnt/styles/named_style.hpp
+++ b/include/xlnt/styles/named_style.hpp
@@ -23,68 +23,25 @@
 // @author: see AUTHORS file
 #pragma once
 
-#include "alignment.hpp"
-#include "borders.hpp"
-#include "fill.hpp"
-#include "font.hpp"
-#include "number_format.hpp"
-#include "protection.hpp"
+#include "style.hpp"
 
 namespace xlnt {
 
-class workbook;
-
-class style
+class named_style
 {
 public:
-    style();
+    named_style();
     
     std::size_t hash() const;
     
-    const alignment get_alignment() const;
-    const border get_border() const;
-    const fill get_fill() const;
-    const font get_font() const;
-    const number_format get_number_format() const;
-    const protection get_protection() const;
-    bool pivot_button() const;
-    bool quote_prefix() const;
-    
-    std::size_t get_fill_index() const { return fill_index_; }
-    std::size_t get_font_index() const { return font_index_; }
-    std::size_t get_border_index() const { return border_index_; }
-    std::size_t get_number_format_index() const { return number_format_index_; }
-    
-    bool operator==(const style &other) const
+    bool operator==(const named_style &other) const
     {
-        return hash() == other.hash();
+        return style_.hash() == other.style_.hash();
     }
     
 private:
-    friend class workbook;
-    
-    std::size_t style_index_;
-    
-    std::size_t alignment_index_;
-    alignment alignment_;
-    
-    std::size_t border_index_;
-    border border_;
-    
-    std::size_t fill_index_;
-    fill fill_;
-    
-    std::size_t font_index_;
-    font font_;
-    
-    std::size_t number_format_index_;
-    number_format number_format_;
-    
-    std::size_t protection_index_;
-    protection protection_;
-    
-    bool pivot_button_;
-    bool quote_prefix_;
+    std::string name_;
+    style style_;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/number_format.hpp b/include/xlnt/styles/number_format.hpp
index b551f4d1..0cb53ff4 100644
--- a/include/xlnt/styles/number_format.hpp
+++ b/include/xlnt/styles/number_format.hpp
@@ -32,80 +32,52 @@ namespace xlnt {
 class number_format
 {
 public:
-    enum class format
-    {
-        general,
-        text,
-        number,
-        number_00,
-        number_comma_separated1,
-        number_comma_separated2,
-        percentage,
-        percentage_00,
-        date_yyyymmdd2,
-        date_yyyymmdd,
-        date_ddmmyyyy,
-        date_dmyslash,
-        date_dmyminus,
-        date_dmminus,
-        date_myminus,
-        date_xlsx14,
-        date_xlsx15,
-        date_xlsx16,
-        date_xlsx17,
-        date_xlsx22,
-        date_datetime,
-        date_time1,
-        date_time2,
-        date_time3,
-        date_time4,
-        date_time5,
-        date_time6,
-        date_time7,
-        date_time8,
-        date_timedelta,
-        date_yyyymmddslash,
-        currency_usd_simple,
-        currency_usd,
-        currency_eur_simple,
-        unknown
-    };
+    static const number_format general();
+    static const number_format text();
+    static const number_format number();
+    static const number_format number_00();
+    static const number_format number_comma_separated1();
+    static const number_format number_comma_separated2();
+    static const number_format percentage();
+    static const number_format percentage_00();
+    static const number_format date_yyyymmdd2();
+    static const number_format date_yyyymmdd();
+    static const number_format date_ddmmyyyy();
+    static const number_format date_dmyslash();
+    static const number_format date_dmyminus();
+    static const number_format date_dmminus();
+    static const number_format date_myminus();
+    static const number_format date_xlsx14();
+    static const number_format date_xlsx15();
+    static const number_format date_xlsx16();
+    static const number_format date_xlsx17();
+    static const number_format date_xlsx22();
+    static const number_format date_datetime();
+    static const number_format date_time1();
+    static const number_format date_time2();
+    static const number_format date_time3();
+    static const number_format date_time4();
+    static const number_format date_time5();
+    static const number_format date_time6();
+    static const number_format date_time7();
+    static const number_format date_time8();
+    static const number_format date_timedelta();
+    static const number_format date_yyyymmddslash();
+    static const number_format currency_usd_simple();
+    static const number_format currency_usd();
+    static const number_format currency_eur_simple();
 
-    struct format_hash
-    {
-        std::size_t operator()(format f) const
-        {
-	    return std::hash<int>()((int)f);
-	}
-    };
-    
-    static const std::unordered_map<format, std::string, format_hash> &format_strings();    
-    static const std::unordered_map<int, std::string> &builtin_formats();
-    static const std::unordered_map<std::string, int> &reversed_builtin_formats();    
-
-    static std::string builtin_format_code(int index);
-    static format lookup_format(int code);
-    
-    static bool is_builtin(const std::string &format);
-    
-    static const number_format &default_number_format()
-    {
-        static number_format default_;
-        return default_;
-    }
+    static number_format from_builtin_id(int builtin_id);
     
     number_format();
-    number_format(format code);
-    number_format(const std::string &code);
+    number_format(int builtin_id);
+    number_format(const std::string &code, int custom_id = -1);
     
-    format get_format_code() const;
-    
-    void set_format_code(format format_code);
-    
-    void set_format_string(const std::string &format_code);
+    void set_format_string(const std::string &format_code, int id = -1);
     std::string get_format_string() const;
-    
-    int get_format_index() const { return format_index_; }
+
+    void set_id(int id) { id_ = id; }
+    int get_id() const { return id_; }
     
     std::size_t hash() const;
     
@@ -115,8 +87,7 @@ public:
     }
 
 private:
-    format format_code_;
-    int format_index_;
+    int id_;
     std::string format_string_;
 };
 
diff --git a/include/xlnt/styles/pattern_fill.hpp b/include/xlnt/styles/pattern_fill.hpp
deleted file mode 100644
index 079cb249..00000000
--- a/include/xlnt/styles/pattern_fill.hpp
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright (c) 2015 Thomas Fussell
-// Copyright (c) 2010-2015 openpyxl
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, WRISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE
-//
-// @license: http://www.opensource.org/licenses/mit-license.php
-// @author: see AUTHORS file
-#pragma once
-
-#include "color.hpp"
-
-namespace xlnt {
-
-class pattern_fill : public fill
-{
-public:
-    void set_pattern_type(const std::string &type) { type_ = type; }
-    void set_foreground_color(const std::string &hex) { foreground_color_ = hex; }
-    
-    std::size_t hash() const override { return 0; }
-    
-private:
-    std::string type_;
-    std::string foreground_color_;
-};
-
-} // namespace xlnt
diff --git a/include/xlnt/styles/protection.hpp b/include/xlnt/styles/protection.hpp
index 71e8dc42..a64315cd 100644
--- a/include/xlnt/styles/protection.hpp
+++ b/include/xlnt/styles/protection.hpp
@@ -25,6 +25,8 @@
 
 #include <cstddef>
 
+#include <xlnt/common/hash_combine.hpp>
+
 namespace xlnt {
 
 class protection
@@ -40,9 +42,14 @@ public:
     protection();
     protection(type locked);
     
-    void set_locked(bool locked)
+    void set_locked(type locked_type)
     {
-        locked_ = locked ? type::protected_ : type::unprotected;
+        locked_ = locked_type;
+    }
+    
+    void set_hidden(type hidden_type)
+    {
+        hidden_ = hidden_type;
     }
     
     bool operator==(const protection &other) const
@@ -50,7 +57,13 @@ public:
         return hash() == other.hash();
     }
     
-    std::size_t hash() const { return 0; }
+    std::size_t hash() const
+    {
+        std::size_t seed = static_cast<std::size_t>(locked_);
+        hash_combine(seed, static_cast<std::size_t>(hidden_));
+        
+        return seed;
+    }
     
 private:
     type locked_;
diff --git a/include/xlnt/styles/side.hpp b/include/xlnt/styles/side.hpp
index ee78097a..86145a42 100644
--- a/include/xlnt/styles/side.hpp
+++ b/include/xlnt/styles/side.hpp
@@ -25,7 +25,7 @@
 
 #include <cstddef>
 
-#include <xlnt/styles/color.hpp>
+#include "../common/hash_combine.hpp"
 
 namespace xlnt {
 
@@ -50,16 +50,81 @@ enum class border_style
 class side
 {
 public:
-    side(border_style style = border_style::none, color = color::black);
+    enum class color_type
+    {
+        theme,
+        indexed
+    };
+    
+    side();
+    
+    std::size_t hash() const
+    {
+        std::size_t seed = 0;
+        
+        if(style_assigned_)
+        {
+            hash_combine(seed, static_cast<std::size_t>(style_));
+        }
+        
+        if(color_assigned_)
+        {
+            hash_combine(seed, static_cast<std::size_t>(color_type_));
+            hash_combine(seed, color_);
+        }
+        
+        return seed;
+    }
+    
+    border_style get_style() const
+    {
+        return style_;
+    }
+    
+    color_type get_color_type() const
+    {
+        return color_type_;
+    }
+    
+    std::size_t get_color() const
+    {
+        return color_;
+    }
+    
+    bool is_style_assigned() const
+    {
+        return style_assigned_;
+    }
+    
+    bool is_color_assigned() const
+    {
+        return color_assigned_;
+    }
     
     bool operator==(const side &other) const
     {
-        return other.style_ == style_;
+        return other.style_ == style_ && color_type_ == other.color_type_ && color_ == other.color_;
+    }
+    
+    void set_border_style(border_style bs)
+    {
+        style_assigned_ = true;
+        style_ = bs;
+    }
+    
+    void set_color(color_type type, std::size_t color)
+    {
+        color_assigned_ = true;
+        color_type_ = type;
+        color_ = color;
     }
     
 private:
-    border_style style_;
-    color color_;
+    bool style_assigned_ = false;
+    border_style style_ = border_style::none;
+    bool color_assigned_ = false;
+    color_type color_type_ = color_type::indexed;
+    std::size_t color_ = 0;
 };
     
 } // namespace xlnt
diff --git a/include/xlnt/styles/style.hpp b/include/xlnt/styles/style.hpp
index cd0ce529..01cbe63b 100644
--- a/include/xlnt/styles/style.hpp
+++ b/include/xlnt/styles/style.hpp
@@ -38,6 +38,8 @@ class style
 {
 public:
     style();
+    style(const style &other);
+    style &operator=(const style &other);
     
     std::size_t hash() const;
     
@@ -50,10 +52,19 @@ public:
     bool pivot_button() const;
     bool quote_prefix() const;
     
-    std::size_t get_fill_index() const { return fill_index_; }
-    std::size_t get_font_index() const { return font_index_; }
-    std::size_t get_border_index() const { return border_index_; }
-    std::size_t get_number_format_index() const { return number_format_index_; }
+    std::size_t get_id() const { return id_; }
+    
+    std::size_t get_fill_id() const { return fill_id_; }
+    std::size_t get_font_id() const { return font_id_; }
+    std::size_t get_border_id() const { return border_id_; }
+    std::size_t get_number_format_id() const { return number_format_id_; }
+    
+    void apply_alignment(bool apply) { alignment_apply_ = apply; }
+    void apply_border(bool apply) { border_apply_ = apply; }
+    void apply_fill(bool apply) { fill_apply_ = apply; }
+    void apply_font(bool apply) { font_apply_ = apply; }
+    void apply_number_format(bool apply) { number_format_apply_ = apply; }
+    void apply_protection(bool apply) { protection_apply_ = apply; }
     
     bool operator==(const style &other) const
     {
@@ -61,26 +72,32 @@ public:
     }
     
 private:
+    friend class style_reader;
+    friend class style_writer;
     friend class workbook;
     
-    std::size_t style_index_;
+    std::size_t id_;
     
-    std::size_t alignment_index_;
+    bool alignment_apply_;
     alignment alignment_;
     
-    std::size_t border_index_;
+    bool border_apply_;
+    std::size_t border_id_;
     border border_;
     
-    std::size_t fill_index_;
+    bool fill_apply_;
+    std::size_t fill_id_;
     fill fill_;
     
-    std::size_t font_index_;
+    bool font_apply_;
+    std::size_t font_id_;
     font font_;
     
-    std::size_t number_format_index_;
+    bool number_format_apply_;
+    std::size_t number_format_id_;
     number_format number_format_;
     
-    std::size_t protection_index_;
+    bool protection_apply_;
     protection protection_;
     
     bool pivot_button_;
diff --git a/include/xlnt/workbook/workbook.hpp b/include/xlnt/workbook/workbook.hpp
index c27709cd..49949723 100644
--- a/include/xlnt/workbook/workbook.hpp
+++ b/include/xlnt/workbook/workbook.hpp
@@ -177,7 +177,7 @@ public:
     bool save(const std::string &filename);
     bool load(const std::vector<unsigned char> &data);
     bool load(const std::string &filename);
-    bool load(const std::istream &stream);
+    bool load(std::istream &stream);
     bool load(zip_file &archive);
     
     bool operator==(const workbook &rhs) const;
@@ -200,22 +200,20 @@ public:
 	relationship get_relationship(const std::string &id) const;
     std::vector<relationship> get_relationships() const;
     
-    void add_alignment(alignment a);
-    void add_border(border b);
-    void add_fill(fill &f);
-    void add_font(font f);
-    void add_protection(protection p);
-    void add_color(color c);
-    void add_number_format(const std::string &format);
+    void add_alignment(const alignment &a);
+    void add_border(const border &b);
+    void add_fill(const fill &f);
+    void add_font(const font &f);
+    void add_color(const color &c);
+    void add_number_format(const number_format &format);
+    void add_protection(const protection &p);
     
     std::vector<style> get_styles() const;
     
-    std::vector<alignment> get_alignments() const;
     std::vector<border> get_borders() const;
     std::vector<fill> get_fills() const;
     std::vector<font> get_fonts() const;
     std::vector<number_format> get_number_formats() const;
-    std::vector<protection> get_protections() const;
     
     const number_format &get_number_format(std::size_t style_id) const;
     std::size_t set_number_format(const number_format &format, std::size_t style_id);
@@ -237,8 +235,8 @@ public:
     bool has_loaded_theme();
     std::string get_loaded_theme();
     
-    style get_style(std::size_t style_id);
-    std::size_t add_style(style style_);
+    const style &get_style(std::size_t style_id) const;
+    std::size_t add_style(const style &style_);
     
 private:
     friend class worksheet;
diff --git a/include/xlnt/writer/excel_writer.hpp b/include/xlnt/writer/excel_writer.hpp
index fe89ecc4..e26973ed 100644
--- a/include/xlnt/writer/excel_writer.hpp
+++ b/include/xlnt/writer/excel_writer.hpp
@@ -23,11 +23,34 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <string>
+#include <vector>
+
 namespace xlnt {
 
+class workbook;
+class zip_file;
+
 class excel_writer
 {
-
+public:
+    excel_writer(workbook &wb);
+    
+    void save(const std::string &filename, bool as_template);
+    
+    void write_data(zip_file &archive, bool as_template);
+    void write_shared_strings(zip_file &archive, const std::vector<std::string> &shared_strings);
+    void write_images(zip_file &archive);
+    void write_charts(zip_file &archive);
+    void write_chartsheets(zip_file &archive);
+    void write_worksheets(zip_file &archive, const std::vector<std::string> &shared_strings);
+    void write_external_links(zip_file &archive);
+    
+private:
+    workbook wb_;
 };
+    
+bool save_workbook(workbook &wb, const std::string &filename, bool as_template = false);
+std::vector<std::uint8_t> save_virtual_workbook(xlnt::workbook &wb, bool as_template = false);
 
 } // namespace xlnt
diff --git a/include/xlnt/writer/workbook_writer.hpp b/include/xlnt/writer/workbook_writer.hpp
index 00b7cc23..7a53a810 100644
--- a/include/xlnt/writer/workbook_writer.hpp
+++ b/include/xlnt/writer/workbook_writer.hpp
@@ -30,29 +30,6 @@
 
 namespace xlnt {
 
-class workbook;
-class zip_file;
-
-class excel_writer
-{
-public:
-    excel_writer(workbook &wb);
-    
-    void save(const std::string &filename, bool as_template);
-    void write_data(zip_file &archive, bool as_template);
-    void write_string_table(zip_file &archive);
-    void write_images(zip_file &archive);
-    void write_charts(zip_file &archive);
-    void write_chartsheets(zip_file &archive);
-    void write_worksheets(zip_file &archive);
-    void write_external_links(zip_file &archive);
-    
-private:
-    workbook wb_;
-    style_writer style_writer_;
-    std::vector<std::string> shared_strings_;
-};
-
 std::string write_shared_strings(const std::vector<std::string> &string_table);
 std::string write_properties_core(const document_properties &prop);
 std::string write_worksheet_rels(worksheet ws);
@@ -63,7 +40,4 @@ std::string write_workbook(const workbook &wb);
 std::string write_workbook_rels(const workbook &wb);
 std::string write_defined_names(const xlnt::workbook &wb);
     
-bool save_workbook(workbook &wb, const std::string &filename, bool as_template = false);
-std::vector<std::uint8_t> save_virtual_workbook(xlnt::workbook &wb, bool as_template = false);
-
 } // namespace xlnt
diff --git a/source/cell/cell.cpp b/source/cell/cell.cpp
index 7631a3e2..f39f2d15 100644
--- a/source/cell/cell.cpp
+++ b/source/cell/cell.cpp
@@ -558,9 +558,6 @@ std::string format_text(const std::string &text, const std::string &format)
 
 namespace xlnt {
     
-const xlnt::color xlnt::color::black(0);
-const xlnt::color xlnt::color::white(1);
-    
 const std::unordered_map<std::string, int> cell::ErrorCodes =
 {
     {"#NULL!", 0},
@@ -594,7 +591,7 @@ cell::cell(worksheet worksheet, const cell_reference &reference, const T &initia
     
 bool cell::garbage_collectible() const
 {
-    return !(get_data_type() != type::null || is_merged() || has_comment() || has_formula());
+    return !(get_data_type() != type::null || is_merged() || has_comment() || has_formula() || has_style());
 }
 
 
@@ -737,7 +734,7 @@ void cell::set_value(date d)
 {
     d_->type_ = type::numeric;
     d_->value_numeric_ = d.to_number(get_base_date());
-    set_number_format(number_format(number_format::format::date_yyyymmdd2));
+    set_number_format(number_format::date_yyyymmdd2());
 }
 
 template<>
@@ -745,7 +742,7 @@ void cell::set_value(datetime d)
 {
     d_->type_ = type::numeric;
     d_->value_numeric_ = d.to_number(get_base_date());
-    set_number_format(number_format(number_format::format::date_datetime));
+    set_number_format(number_format::date_datetime());
 }
 
 template<>
@@ -753,7 +750,7 @@ void cell::set_value(time t)
 {
     d_->type_ = type::numeric;
     d_->value_numeric_ = t.to_number();
-    set_number_format(number_format(number_format::format::date_time6));
+    set_number_format(number_format::date_time6());
 }
 
 template<>
@@ -761,7 +758,7 @@ void cell::set_value(timedelta t)
 {
     d_->type_ = type::numeric;
     d_->value_numeric_ = t.to_number();
-    set_number_format(number_format(number_format::format::date_timedelta));
+    set_number_format(number_format::date_timedelta());
 }
 
 row_t cell::get_row() const
@@ -1035,13 +1032,15 @@ std::size_t cell::get_xf_index() const
 
 const number_format &cell::get_number_format() const
 {
+    static const number_format default_format;
+    
     if(d_->has_style_)
     {
         return get_parent().get_parent().get_number_format(d_->style_id_);
     }
     else if(get_parent().get_parent().get_number_formats().empty())
     {
-        return number_format::default_number_format();
+        return default_format;
     }
     else
     {
@@ -1238,6 +1237,17 @@ std::size_t cell::get_style_id() const
 {
     return d_->style_id_;
 }
+
+bool cell::has_style() const
+{
+    return d_->has_style_;
+}
+
+void cell::set_style_id(std::size_t style_id)
+{
+    d_->style_id_ = style_id;
+    d_->has_style_ = true;
+}
     
 calendar cell::get_base_date() const
 {
diff --git a/source/detail/cell_impl.hpp b/source/detail/cell_impl.hpp
index da61dac1..e10ffee3 100644
--- a/source/detail/cell_impl.hpp
+++ b/source/detail/cell_impl.hpp
@@ -152,7 +152,7 @@ struct cell_impl
             {
                 value_numeric_ = percentage.second;
                 type_ = cell::type::numeric;
-                self().set_number_format(xlnt::number_format(xlnt::number_format::format::percentage));
+                self().set_number_format(xlnt::number_format::percentage());
             }
             else
             {
@@ -161,7 +161,7 @@ struct cell_impl
                 if (time.first)
                 {
                     type_ = cell::type::numeric;
-                    self().set_number_format(xlnt::number_format(number_format::format::date_time6));
+                    self().set_number_format(number_format::date_time6());
                     value_numeric_ = time.second.to_number();
                 }
                 else
diff --git a/source/detail/workbook_impl.hpp b/source/detail/workbook_impl.hpp
index ce886a07..723ccb31 100644
--- a/source/detail/workbook_impl.hpp
+++ b/source/detail/workbook_impl.hpp
@@ -19,12 +19,10 @@ struct workbook_impl
         guess_types_(other.guess_types_),
         data_only_(other.data_only_),
         styles_(other.styles_),
-        alignments_(other.alignments_),
         borders_(other.borders_),
         fills_(other.fills_),
         fonts_(other.fonts_),
-        number_formats_(other.number_formats_),
-        protections_(other.protections_)
+        number_formats_(other.number_formats_)
     {
     }
     
@@ -41,12 +39,10 @@ struct workbook_impl
         guess_types_ = other.guess_types_;
         data_only_ = other.data_only_;
         styles_ = other.styles_;
-        alignments_ = other.alignments_;
         borders_ = other.borders_;
         fills_ = other.fills_;
         fonts_ = other.fonts_;
         number_formats_ = other.number_formats_;
-        protections_ = other.protections_;
         
         return *this;
     }
@@ -63,12 +59,12 @@ struct workbook_impl
     
     std::vector<style> styles_;
     
-    std::vector<alignment> alignments_;
+    std::size_t next_custom_format_id_;
+    
     std::vector<border> borders_;
     std::vector<fill> fills_;
     std::vector<font> fonts_;
     std::vector<number_format> number_formats_;
-    std::vector<protection> protections_;
     
 };
 
diff --git a/source/reader/excel_reader.cpp b/source/reader/excel_reader.cpp
index 3c792061..3d530aa4 100644
--- a/source/reader/excel_reader.cpp
+++ b/source/reader/excel_reader.cpp
@@ -1,5 +1,17 @@
+#include <xlnt/common/datetime.hpp>
+#include <xlnt/common/exceptions.hpp>
+#include <xlnt/common/zip_file.hpp>
+#include <xlnt/styles/style.hpp>
 #include <xlnt/reader/excel_reader.hpp>
+#include <xlnt/reader/shared_strings_reader.hpp>
+#include <xlnt/reader/style_reader.hpp>
+#include <xlnt/reader/workbook_reader.hpp>
+#include <xlnt/reader/worksheet_reader.hpp>
+#include <xlnt/workbook/document_properties.hpp>
 #include <xlnt/workbook/workbook.hpp>
+#include <xlnt/worksheet/worksheet.hpp>
+
+#include "detail/include_pugixml.hpp"
 
 namespace {
     
@@ -20,17 +32,92 @@ std::string::size_type find_string_in_string(const std::string &string, const st
     return possible_match_index;
 }
 
+xlnt::workbook load_workbook(xlnt::zip_file &archive, bool guess_types, bool data_only)
+{
+    xlnt::workbook wb;
+    
+    wb.set_guess_types(guess_types);
+    wb.set_data_only(data_only);
+    
+    auto content_types = xlnt::read_content_types(archive);
+    auto type = xlnt::determine_document_type(content_types);
+    
+    if(type != "excel")
+    {
+        throw xlnt::invalid_file_exception("");
+    }
+    
+    wb.clear();
+    
+    auto workbook_relationships = read_relationships(archive, "xl/workbook.xml");
+    
+    for(auto relationship : workbook_relationships)
+    {
+        wb.create_relationship(relationship.get_id(), relationship.get_target_uri(), relationship.get_type());
+    }
+    
+    pugi::xml_document doc;
+    doc.load(archive.read("xl/workbook.xml").c_str());
+    
+    auto root_node = doc.child("workbook");
+    
+    auto workbook_pr_node = root_node.child("workbookPr");
+    wb.get_properties().excel_base_date = (workbook_pr_node.attribute("date1904") != nullptr && workbook_pr_node.attribute("date1904").as_int() != 0) ? xlnt::calendar::mac_1904 : xlnt::calendar::windows_1900;
+    
+    auto sheets_node = root_node.child("sheets");
+    
+    xlnt::shared_strings_reader shared_strings_reader_;
+    auto shared_strings = shared_strings_reader_.read_strings(archive);
+    
+    xlnt::style_reader style_reader_(wb);
+    style_reader_.read_styles(archive);
+    
+    for(const auto &border_ : style_reader_.get_borders())
+    {
+        wb.add_border(border_);
+    }
+    
+    for(const auto &fill_ : style_reader_.get_fills())
+    {
+        wb.add_fill(fill_);
+    }
+    
+    for(const auto &font_ : style_reader_.get_fonts())
+    {
+        wb.add_font(font_);
+    }
+    
+    for(const auto &number_format_ : style_reader_.get_number_formats())
+    {
+        wb.add_number_format(number_format_);
+    }
+    
+    for(const auto &style : style_reader_.get_styles())
+    {
+        wb.add_style(style);
+    }
+    
+    for(auto sheet_node : sheets_node.children("sheet"))
+    {
+        auto rel = wb.get_relationship(sheet_node.attribute("r:id").as_string());
+        auto ws = wb.create_sheet(sheet_node.attribute("name").as_string(), rel);
+        
+        xlnt::read_worksheet(ws, archive, rel, shared_strings);
+    }
+    
+    return wb;
+}
     
 } // namespace
 
 namespace xlnt {
 
-std::string CentralDirectorySignature()
+std::string excel_reader::CentralDirectorySignature()
 {
     return "\x50\x4b\x05\x06";
 }
 
-std::string repair_central_directory(const std::string &original)
+std::string excel_reader::repair_central_directory(const std::string &original)
 {
     auto pos = find_string_in_string(original, CentralDirectorySignature());
     
@@ -42,26 +129,36 @@ std::string repair_central_directory(const std::string &original)
     return original;
 }
 
-workbook load_workbook(const std::string &filename, bool guess_types, bool data_only)
+workbook excel_reader::load_workbook(std::istream &stream, bool guess_types, bool data_only)
 {
-    workbook wb;
+    std::vector<std::uint8_t> bytes((std::istream_iterator<char>(stream)),
+                                    std::istream_iterator<char>());
     
-    wb.set_guess_types(guess_types);
-    wb.set_data_only(data_only);
-    wb.load(filename);
-    
-    return wb;
+    return load_workbook(bytes, guess_types, data_only);
 }
 
-xlnt::workbook load_workbook(const std::vector<std::uint8_t> &bytes, bool guess_types, bool data_only)
+workbook excel_reader::load_workbook(const std::string &filename, bool guess_types, bool data_only)
 {
-    xlnt::workbook wb;
-
-    wb.set_guess_types(guess_types);
-    wb.set_data_only(data_only);
-    wb.load(bytes);
+    xlnt::zip_file archive;
     
-    return wb;
+    try
+    {
+        archive.load(filename);
+    }
+    catch(std::runtime_error)
+    {
+        throw invalid_file_exception(filename);
+    }
+    
+    return ::load_workbook(archive, guess_types, data_only);
+}
+
+xlnt::workbook excel_reader::load_workbook(const std::vector<std::uint8_t> &bytes, bool guess_types, bool data_only)
+{
+    xlnt::zip_file archive;
+    archive.load(bytes);
+    
+    return ::load_workbook(archive, guess_types, data_only);
 }
     
 } // namespace xlnt
diff --git a/source/reader/shared_strings_reader.cpp b/source/reader/shared_strings_reader.cpp
index 49c910fe..252be95f 100644
--- a/source/reader/shared_strings_reader.cpp
+++ b/source/reader/shared_strings_reader.cpp
@@ -1,17 +1,26 @@
+#include <xlnt/common/zip_file.hpp>
 #include <xlnt/reader/shared_strings_reader.hpp>
 
 #include "detail/include_pugixml.hpp"
 
 namespace xlnt {
 
-std::vector<std::string> read_shared_strings(const std::string &xml_string)
+std::vector<std::string> shared_strings_reader::read_strings(zip_file &archive)
 {
-    std::vector<std::string> shared_strings;
+    static const std::string shared_strings_filename = "xl/sharedStrings.xml";
+    
+    if(!archive.has_file(shared_strings_filename))
+    {
+        return { };
+    }
+    
     pugi::xml_document doc;
-    doc.load(xml_string.c_str());
+    doc.load(archive.read(shared_strings_filename).c_str());
+    
     auto root_node = doc.child("sst");
-    //int count = root_node.attribute("count").as_int();
     int unique_count = root_node.attribute("uniqueCount").as_int();
+ 
+    std::vector<std::string> shared_strings;
     
     for(auto si_node : root_node)
     {
diff --git a/source/reader/style_reader.cpp b/source/reader/style_reader.cpp
new file mode 100644
index 00000000..63ce8c75
--- /dev/null
+++ b/source/reader/style_reader.cpp
@@ -0,0 +1,505 @@
+#include <xlnt/common/zip_file.hpp>
+#include <xlnt/styles/border.hpp>
+#include <xlnt/styles/fill.hpp>
+#include <xlnt/styles/font.hpp>
+#include <xlnt/styles/named_style.hpp>
+#include <xlnt/styles/number_format.hpp>
+#include <xlnt/styles/style.hpp>
+#include <xlnt/reader/style_reader.hpp>
+
+#include "detail/include_pugixml.hpp"
+
+namespace xlnt {
+
+protection read_protection(pugi::xml_node node)
+{
+    auto prot_type_from_string = [](const std::string &type_string)
+    {
+        if(type_string == "true") return protection::type::protected_;
+        else if(type_string == "inherit") return protection::type::inherit;
+        return protection::type::unprotected;
+    };
+ 
+    protection prot;
+    prot.set_locked(prot_type_from_string(node.attribute("locked").as_string()));
+    prot.set_hidden(prot_type_from_string(node.attribute("hidden").as_string()));
+    return prot;
+}
+    
+alignment read_alignment(pugi::xml_node node)
+{
+    alignment align;
+    
+    align.set_wrap_text(node.attribute("wrapText").as_int() != 0);
+    
+    bool has_vertical = node.attribute("vertical") != nullptr;
+    std::string vertical = has_vertical ? node.attribute("vertical").as_string() : "";
+    
+    if(has_vertical)
+    {
+        if(vertical == "bottom")
+        {
+            align.set_vertical(alignment::vertical_alignment::bottom);
+        }
+        else if(vertical =="center")
+        {
+            align.set_vertical(alignment::vertical_alignment::center);
+        }
+        else if(vertical =="justify")
+        {
+            align.set_vertical(alignment::vertical_alignment::justify);
+        }
+        else if(vertical =="top")
+        {
+            align.set_vertical(alignment::vertical_alignment::top);
+        }
+        else
+        {
+            throw "unknown alignment";
+        }
+    }
+    
+    bool has_horizontal = node.attribute("horizontal") != nullptr;
+    std::string horizontal = has_horizontal ? node.attribute("horizontal").as_string() : "";
+    
+    if(has_horizontal)
+    {
+        if(horizontal == "left")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::left);
+        }
+        else if(horizontal == "center")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::center);
+        }
+        else if(horizontal == "center-continuous")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::center_continuous);
+        }
+        else if(horizontal == "right")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::right);
+        }
+        else if(horizontal == "justify")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::justify);
+        }
+        else if(horizontal == "general")
+        {
+            align.set_horizontal(alignment::horizontal_alignment::general);
+        }
+        else
+        {
+            throw "unknown alignment";
+        }
+    }
+    
+    return align;
+}
+
+style style_reader::read_style(pugi::xml_node stylesheet_node, pugi::xml_node xf_node)
+{
+    style s;
+    
+    s.apply_number_format(xf_node.attribute("applyNumberFormat").as_bool());
+    s.number_format_id_ = xf_node.attribute("numFmtId").as_int();
+    
+    bool builtin_format = true;
+    
+    for(auto num_fmt : number_formats_)
+    {
+        if(num_fmt.get_id() == s.get_number_format_id())
+        {
+            s.number_format_ = num_fmt;
+            builtin_format = false;
+            break;
+        }
+    }
+    
+    if(builtin_format)
+    {
+        s.number_format_ = number_format::from_builtin_id(s.get_number_format_id());
+    }
+    
+    s.apply_font(xf_node.attribute("applyFont").as_bool());
+    s.font_id_ = xf_node.attribute("fontId") != nullptr ? xf_node.attribute("fontId").as_int() : 0;
+    s.font_ = fonts_[s.font_id_];
+    
+    s.apply_fill(xf_node.attribute("applyFill").as_bool());
+    s.fill_id_ = xf_node.attribute("fillId").as_int();
+    s.fill_ = fills_[s.fill_id_];
+    
+    s.apply_border(xf_node.attribute("applyBorder").as_bool());
+    s.border_id_ = xf_node.attribute("borderId").as_int();
+    s.border_ = borders_[s.border_id_];
+    
+    s.apply_protection(xf_node.attribute("protection") != nullptr);
+    
+    if(s.protection_apply_)
+    {
+        auto inline_protection = read_protection(xf_node.child("protection"));
+        s.protection_ = inline_protection;
+    }
+    
+    s.apply_alignment(xf_node.child("alignment") != nullptr);
+    
+    if(s.alignment_apply_)
+    {
+        auto inline_alignment = read_alignment(xf_node.child("alignment"));
+        s.alignment_ = inline_alignment;
+    }
+    
+    return s;
+}
+
+style_reader::style_reader(workbook &wb)
+{
+
+}
+
+void style_reader::read_styles(zip_file &archive)
+{
+    auto xml = archive.read("xl/styles.xml");
+    
+    pugi::xml_document doc;
+    doc.load_string(xml.c_str());
+    
+    auto root = doc.root();
+    auto stylesheet_node = root.child("styleSheet");
+    
+    read_borders(stylesheet_node.child("borders"));
+    read_fills(stylesheet_node.child("fills"));
+    read_fonts(stylesheet_node.child("fonts"));
+    read_number_formats(stylesheet_node.child("numFmts"));
+    
+    auto cell_xfs_node = stylesheet_node.child("cellXfs");
+    
+    for(auto xf_node : cell_xfs_node.children("xf"))
+    {
+        styles_.push_back(read_style(stylesheet_node, xf_node));
+        styles_.back().id_ = styles_.size() - 1;
+    }
+
+    read_color_index();
+    read_dxfs();
+    read_cell_styles();
+    read_named_styles(root.child("namedStyles"));
+}
+
+void style_reader::read_number_formats(pugi::xml_node num_fmts_node)
+{
+    for(auto num_fmt_node : num_fmts_node.children("numFmt"))
+    {
+        number_format nf;
+        
+        nf.set_format_string(num_fmt_node.attribute("formatCode").as_string());
+        nf.set_id(num_fmt_node.attribute("numFmtId").as_int());
+        
+        number_formats_.push_back(nf);
+    }
+}
+
+void style_reader::read_color_index()
+{
+    
+}
+    
+void style_reader::read_dxfs()
+{
+    
+}
+
+void style_reader::read_fonts(pugi::xml_node fonts_node)
+{
+    for(auto font_node : fonts_node)
+    {
+        font new_font;
+        
+        new_font.set_size(font_node.child("sz").attribute("val").as_int());
+        new_font.set_name(font_node.child("name").attribute("val").as_string());
+        
+        if(font_node.child("color").attribute("theme") != nullptr)
+        {
+            new_font.set_color(color(color::type::theme, font_node.child("color").attribute("theme").as_ullong()));
+        }
+        else if(font_node.child("color").attribute("indexed") != nullptr)
+        {
+            new_font.set_color(color(color::type::indexed, font_node.child("color").attribute("indexed").as_ullong()));
+        }
+        
+        if(font_node.child("family") != nullptr)
+        {
+            new_font.set_family(font_node.child("family").attribute("val").as_int());
+        }
+        
+        if(font_node.child("scheme") != nullptr)
+        {
+            new_font.set_scheme(font_node.child("scheme").attribute("val").as_string());
+        }
+        
+        if(font_node.child("b") != nullptr)
+        {
+            new_font.set_bold(font_node.child("b").attribute("val").as_bool());
+        }
+        
+        fonts_.push_back(new_font);
+    }
+}
+
+void style_reader::read_fills(pugi::xml_node fills_node)
+{
+    auto pattern_fill_type_from_string = [](const std::string &fill_type)
+    {
+        if(fill_type == "none") return fill::pattern_type::none;
+        if(fill_type == "solid") return fill::pattern_type::solid;
+        if(fill_type == "gray125") return fill::pattern_type::gray125;
+        throw std::runtime_error("invalid fill type");
+    };
+    
+    for(auto fill_node : fills_node)
+    {
+        fill new_fill;
+        
+        if(fill_node.child("patternFill") != nullptr)
+        {
+            auto pattern_fill_node = fill_node.child("patternFill");
+            new_fill.set_type(fill::type::pattern);
+            std::string pattern_type_string = pattern_fill_node.attribute("patternType").as_string();
+            auto pattern_type = pattern_fill_type_from_string(pattern_type_string);
+            new_fill.set_pattern_type(pattern_type);
+            
+            auto bg_color_node = pattern_fill_node.child("bgColor");
+            
+            if(bg_color_node != nullptr)
+            {
+                if(bg_color_node.attribute("indexed") != nullptr)
+                {
+                    new_fill.set_background_color(color(color::type::indexed, bg_color_node.attribute("indexed").as_ullong()));
+                }
+            }
+            
+            auto fg_color_node = pattern_fill_node.child("fgColor");
+            
+            if(fg_color_node != nullptr)
+            {
+                if(fg_color_node.attribute("indexed") != nullptr)
+                {
+                    new_fill.set_foreground_color(color(color::type::indexed, fg_color_node.attribute("indexed").as_ullong()));
+                }
+            }
+        }
+
+        fills_.push_back(new_fill);
+    }
+}
+
+void style_reader::read_borders(pugi::xml_node borders_node)
+{
+    for(auto border_node : borders_node)
+    {
+        border new_border;
+        
+        if(border_node.child("left") != nullptr)
+        {
+            new_border.left_assigned = true;
+            auto left_node = border_node.child("left");
+            
+            if(left_node.attribute("style") != nullptr)
+            {
+                if(left_node.attribute("style").as_string() == std::string("thin"))
+                {
+                    new_border.left.set_border_style(border_style::thin);
+                }
+                else
+                {
+                    throw std::runtime_error("unknown border style");
+                }
+            }
+            
+            auto color_node = left_node.child("color");
+            
+            if(color_node != nullptr)
+            {
+                if(color_node.attribute("indexed") != nullptr)
+                {
+                    new_border.left.set_color(side::color_type::indexed, color_node.attribute("indexed").as_int());
+                }
+                else if(color_node.attribute("theme") != nullptr)
+                {
+                    new_border.left.set_color(side::color_type::theme, color_node.attribute("theme").as_int());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        if(border_node.child("right") != nullptr)
+        {
+            new_border.right_assigned = true;
+            auto right_node = border_node.child("right");
+            
+            if(right_node.attribute("style") != nullptr)
+            {
+                if(right_node.attribute("style").as_string() == std::string("thin"))
+                {
+                    new_border.right.set_border_style(border_style::thin);
+                }
+                else
+                {
+                    throw std::runtime_error("unknown border style");
+                }
+            }
+            
+            auto color_node = right_node.child("color");
+            
+            if(color_node != nullptr)
+            {
+                if(color_node.attribute("indexed") != nullptr)
+                {
+                    new_border.right.set_color(side::color_type::indexed, color_node.attribute("indexed").as_int());
+                }
+                else if(color_node.attribute("theme") != nullptr)
+                {
+                    new_border.right.set_color(side::color_type::theme, color_node.attribute("theme").as_int());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        if(border_node.child("top") != nullptr)
+        {
+            new_border.top_assigned = true;
+            auto top_node = border_node.child("top");
+            
+            if(top_node.attribute("style") != nullptr)
+            {
+                if(top_node.attribute("style").as_string() == std::string("thin"))
+                {
+                    new_border.top.set_border_style(border_style::thin);
+                }
+                else
+                {
+                    throw std::runtime_error("unknown border style");
+                }
+            }
+            
+            auto color_node = top_node.child("color");
+            
+            if(color_node != nullptr)
+            {
+                if(color_node.attribute("indexed") != nullptr)
+                {
+                    new_border.top.set_color(side::color_type::indexed, color_node.attribute("indexed").as_int());
+                }
+                else if(color_node.attribute("theme") != nullptr)
+                {
+                    new_border.top.set_color(side::color_type::theme, color_node.attribute("theme").as_int());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        if(border_node.child("bottom") != nullptr)
+        {
+            new_border.bottom_assigned = true;
+            auto bottom_node = border_node.child("bottom");
+            
+            if(bottom_node.attribute("style") != nullptr)
+            {
+                if(bottom_node.attribute("style").as_string() == std::string("thin"))
+                {
+                    new_border.bottom.set_border_style(border_style::thin);
+                }
+                else
+                {
+                    throw std::runtime_error("unknown border style");
+                }
+            }
+            
+            auto color_node = bottom_node.child("color");
+            
+            if(color_node != nullptr)
+            {
+                if(color_node.attribute("indexed") != nullptr)
+                {
+                    new_border.bottom.set_color(side::color_type::indexed, color_node.attribute("indexed").as_int());
+                }
+                else if(color_node.attribute("theme") != nullptr)
+                {
+                    new_border.bottom.set_color(side::color_type::theme, color_node.attribute("theme").as_int());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        if(border_node.child("diagonal") != nullptr)
+        {
+            new_border.diagonal_assigned = true;
+            auto diagonal_node = border_node.child("diagonal");
+            
+            if(diagonal_node.attribute("style") != nullptr)
+            {
+                if(diagonal_node.attribute("style").as_string() == std::string("thin"))
+                {
+                    new_border.diagonal.set_border_style(border_style::thin);
+                }
+                else
+                {
+                    throw std::runtime_error("unknown border style");
+                }
+            }
+            
+            auto color_node = diagonal_node.child("color");
+            
+            if(color_node != nullptr)
+            {
+                if(color_node.attribute("indexed") != nullptr)
+                {
+                    new_border.diagonal.set_color(side::color_type::indexed, color_node.attribute("indexed").as_int());
+                }
+                else if(color_node.attribute("theme") != nullptr)
+                {
+                    new_border.diagonal.set_color(side::color_type::theme, color_node.attribute("theme").as_int());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        
+        borders_.push_back(new_border);
+    }
+}
+
+void style_reader::read_named_styles(pugi::xml_node named_styles_node)
+{
+}
+    
+void style_reader::read_style_names()
+{
+}
+    
+void style_reader::read_cell_styles()
+{
+    
+}
+    
+void style_reader::read_xfs()
+{
+    
+}
+    
+void style_reader::read_style_table()
+{
+    
+}
+    
+} // namespace xlnt
\ No newline at end of file
diff --git a/source/styles/borders.cpp b/source/styles/borders.cpp
index 14f6a403..03546aa2 100644
--- a/source/styles/borders.cpp
+++ b/source/styles/borders.cpp
@@ -1,9 +1,9 @@
 
-#include <xlnt/styles/border.hpp>
+#include <xlnt/styles/side.hpp>
 
 namespace xlnt {
 
-side::side(border_style style, color c) : style_(style), color_(c)
+side::side()
 {
     
 }
diff --git a/source/styles/number_format.cpp b/source/styles/number_format.cpp
index 35f97446..19e3cf8f 100644
--- a/source/styles/number_format.cpp
+++ b/source/styles/number_format.cpp
@@ -1,11 +1,12 @@
 #include <algorithm>
 #include <regex>
 
+#include <xlnt/common/hash_combine.hpp>
 #include <xlnt/styles/number_format.hpp>
 
-namespace xlnt {
-    
-const std::unordered_map<int, std::string> &number_format::builtin_formats()
+namespace {
+
+const std::unordered_map<int, std::string> &builtin_formats()
 {
     static const std::unordered_map<int, std::string> formats =
     {
@@ -32,23 +33,23 @@ const std::unordered_map<int, std::string> &number_format::builtin_formats()
         {20, "h:mm"},
         {21, "h:mm:ss"},
         {22, "m/d/yy h:mm"},
-
+        
         {37, "#,##0_);(#,##0)"},
         {38, "#,##0_);[Red](#,##0)"},
         {39, "#,##0.00_);(#,##0.00)"},
         {40, "#,##0.00_);[Red](#,##0.00)"},
-
+        
         {41, "_(* #,##0_);_(* \\(#,##0\\);_(* \"-\"_);_(@_)"},
         {42, "_(\"$\"* #,##0_);_(\"$\"* \\(#,##0\\);_(\"$\"* \"-\"_);_(@_)"},
         {43, "_(* #,##0.00_);_(* \\(#,##0.00\\);_(* \"-\"??_);_(@_)"},
-
+        
         {44, "_(\"$\"* #,##0.00_)_(\"$\"* \\(#,##0.00\\)_(\"$\"* \"-\"??_)_(@_)"},
         {45, "mm:ss"},
         {46, "[h]:mm:ss"},
         {47, "mmss.0"},
         {48, "##0.0E+0"},
         {49, "@"}
-
+        
         //EXCEL differs from the standard in the following:
         //{14, "m/d/yyyy"},
         //{22, "m/d/yyyy h:mm"},
@@ -59,101 +60,240 @@ const std::unordered_map<int, std::string> &number_format::builtin_formats()
         //{47, "mm:ss.0"},
         //{55, "yyyy/mm/dd"}
     };
-
-    return formats;
-}
-
-const std::unordered_map<number_format::format, std::string, number_format::format_hash> &number_format::format_strings()
-{
-    static const std::unordered_map<number_format::format, std::string, number_format::format_hash> strings =
-    {
-        {format::general, builtin_formats().at(0)},
-        {format::text, builtin_formats().at(49)},
-        {format::number, builtin_formats().at(1)},
-        {format::number_00, builtin_formats().at(2)},
-        {format::number_comma_separated1, builtin_formats().at(4)},
-        {format::number_comma_separated2, "#,##0.00_-"},
-        {format::percentage, builtin_formats().at(9)},
-        {format::percentage_00, builtin_formats().at(10)},
-        {format::date_yyyymmdd2, "yyyy-mm-dd"},
-        {format::date_yyyymmdd, "yy-mm-dd"},
-        {format::date_ddmmyyyy, "dd/mm/yy"},
-        {format::date_dmyslash, "d/m/y"},
-        {format::date_dmyminus, "d-m-y"},
-        {format::date_dmminus, "d-m"},
-        {format::date_myminus, "m-y"},
-        {format::date_xlsx14, builtin_formats().at(14)},
-        {format::date_xlsx15, builtin_formats().at(15)},
-        {format::date_xlsx16, builtin_formats().at(16)},
-        {format::date_xlsx17, builtin_formats().at(17)},
-        {format::date_xlsx22, builtin_formats().at(22)},
-        {format::date_datetime, "yyyy-mm-dd h:mm:ss"},
-        {format::date_time1, builtin_formats().at(18)},
-        {format::date_time2, builtin_formats().at(19)},
-        {format::date_time3, builtin_formats().at(20)},
-        {format::date_time4, builtin_formats().at(21)},
-        {format::date_time5, builtin_formats().at(45)},
-        {format::date_time6, builtin_formats().at(21)},
-        {format::date_time7, "i:s.S"},
-        {format::date_time8, "h:mm:ss@"},
-        {format::date_timedelta, "[hh]:mm:ss"},
-        {format::date_yyyymmddslash, "yy/mm/dd@"},
-        {format::currency_usd_simple, "\"$\"#,##0.00_-"},
-        {format::currency_usd, "$#,##0_-"},
-        {format::currency_eur_simple, "[$EUR ]#,##0.00_-"}
-    };
-
-    return strings;
-}
-
-const std::unordered_map<std::string, int> &number_format::reversed_builtin_formats()
-{
-    static std::unordered_map<std::string, int> formats;
-    static bool initialised = false;
-
-    if(!initialised)
-    {
-        for(auto format_pair : builtin_formats())
-        {
-            formats[format_pair.second] = format_pair.first;
-        }
-        
-        initialised = true;
-    }
     
     return formats;
 }
+    
+} // namespace
 
-number_format::number_format() : number_format(format::general)
+namespace xlnt {
+
+const number_format number_format::general()
+{
+    static const number_format format(builtin_formats().at(0), 0);
+    return format;
+}
+    
+const number_format number_format::text()
+{
+    static const number_format format(builtin_formats().at(49), 49);
+    return format;
+}
+    
+const number_format number_format::number()
+{
+    static const number_format format(builtin_formats().at(1), 1);
+    return format;
+}
+    
+const number_format number_format::number_00()
+{
+    static const number_format format(builtin_formats().at(2), 2);
+    return format;
+}
+    
+const number_format number_format::number_comma_separated1()
+{
+    static const number_format format(builtin_formats().at(4), 4);
+    return format;
+}
+    
+const number_format number_format::number_comma_separated2()
+{
+    static const number_format format("#,##0.00_-");
+    return format;
+}
+    
+const number_format number_format::percentage()
+{
+    static const number_format format(builtin_formats().at(9), 9);
+    return format;
+}
+    
+const number_format number_format::percentage_00()
+{
+    static const number_format format(builtin_formats().at(10), 10);
+    return format;
+}
+    
+const number_format number_format::date_yyyymmdd2()
+{
+    static const number_format format("yyyy-mm-dd");
+    return format;
+}
+    
+const number_format number_format::date_yyyymmdd()
+{
+    static const number_format format("yy-mm-dd");
+    return format;
+}
+    
+const number_format number_format::date_ddmmyyyy()
+{
+    static const number_format format("dd/mm/yy");
+    return format;
+}
+    
+const number_format number_format::date_dmyslash()
+{
+    static const number_format format("d/m/y");
+    return format;
+}
+    
+const number_format number_format::date_dmyminus()
+{
+    static const number_format format("d-m-y");
+    return format;
+}
+    
+const number_format number_format::date_dmminus()
+{
+    static const number_format format("d-m");
+    return format;
+}
+    
+const number_format number_format::date_myminus()
+{
+    static const number_format format("m-y");
+    return format;
+}
+    
+const number_format number_format::date_xlsx14()
+{
+    static const number_format format(builtin_formats().at(14), 14);
+    return format;
+}
+    
+const number_format number_format::date_xlsx15()
+{
+    static const number_format format(builtin_formats().at(15), 15);
+    return format;
+}
+    
+const number_format number_format::date_xlsx16()
+{
+    static const number_format format(builtin_formats().at(16), 16);
+    return format;
+}
+    
+const number_format number_format::date_xlsx17()
+{
+    static const number_format format(builtin_formats().at(17), 17);
+    return format;
+}
+    
+const number_format number_format::date_xlsx22()
+{
+    static const number_format format(builtin_formats().at(22), 22);
+    return format;
+}
+    
+const number_format number_format::date_datetime()
+{
+    static const number_format format("yyyy-mm-dd h:mm:ss");
+    return format;
+}
+    
+const number_format number_format::date_time1()
+{
+    static const number_format format(builtin_formats().at(18), 18);
+    return format;
+}
+    
+const number_format number_format::date_time2()
+{
+    static const number_format format(builtin_formats().at(19), 19);
+    return format;
+}
+    
+const number_format number_format::date_time3()
+{
+    static const number_format format(builtin_formats().at(20), 20);
+    return format;
+}
+    
+const number_format number_format::date_time4()
+{
+    static const number_format format(builtin_formats().at(21), 21);
+    return format;
+}
+    
+const number_format number_format::date_time5()
+{
+    static const number_format format(builtin_formats().at(45), 45);
+    return format;
+}
+    
+const number_format number_format::date_time6()
+{
+    static const number_format format(builtin_formats().at(21), 21);
+    return format;
+}
+    
+const number_format number_format::date_time7()
+{
+    static const number_format format("i:s.S");
+    return format;
+}
+    
+const number_format number_format::date_time8()
+{
+    static const number_format format("h:mm:ss@");
+    return format;
+}
+    
+const number_format number_format::date_timedelta()
+{
+    static const number_format format("[hh]:mm:ss");
+    return format;
+}
+    
+const number_format number_format::date_yyyymmddslash()
+{
+    static const number_format format("yy/mm/dd@");
+    return format;
+}
+    
+const number_format number_format::currency_usd_simple()
+{
+    static const number_format format("\"$\"#,##0.00_-");
+    return format;
+}
+    
+const number_format number_format::currency_usd()
+{
+    static const number_format format("$#,##0_-");
+    return format;
+}
+    
+const number_format number_format::currency_eur_simple()
+{
+    static const number_format format("[$EUR ]#,##0.00_-");
+    return format;
+}
+
+number_format::number_format() : number_format(general())
 {
 }
 
-number_format::number_format(format code) : format_code_(code), format_index_(0)
+number_format::number_format(int id) : number_format(from_builtin_id(id))
 {
-    set_format_code(code);
 }
 
-number_format::number_format(const std::string &format_string) : number_format(format::general)
+number_format::number_format(const std::string &format_string, int id)
 {
-    set_format_string(format_string);
+    set_format_string(format_string, id);
 }
 
-number_format::format number_format::lookup_format(int code)
+number_format number_format::from_builtin_id(int builtin_id)
 {
-    if(builtin_formats().find(code) == builtin_formats().end())
+    if(builtin_formats().find(builtin_id) == builtin_formats().end())
     {
-        return format::unknown;
+        throw std::runtime_error("unknown id: " + std::to_string(builtin_id));
     }
     
-    auto format_string = builtin_formats().at(code);
-    auto match = std::find_if(format_strings().begin(), format_strings().end(), [&](const std::pair<format, std::string> &p) { return p.second == format_string; });
-    
-    if(match == format_strings().end())
-    {
-        return format::unknown;
-    }
-    
-    return match->first;
+    auto format_string = builtin_formats().at(builtin_id);
+    return number_format(format_string, builtin_id);
 }
 
 std::string number_format::get_format_string() const
@@ -161,53 +301,30 @@ std::string number_format::get_format_string() const
     return format_string_;
 }
 
-number_format::format number_format::get_format_code() const
-{
-    return format_code_;
-}
-
 std::size_t number_format::hash() const
 {
-    std::hash<std::string> hasher;
-    return hasher(format_string_);
+    std::size_t seed = static_cast<std::size_t>(id_);
+    hash_combine(seed, format_string_);
+    
+    return seed;
 }
     
-void number_format::set_format_string(const std::string &format_string)
+void number_format::set_format_string(const std::string &format_string, int id)
 {
     format_string_ = format_string;
-    format_index_ = -1;
-    format_code_ = format::unknown;
+    id_ = id;
     
-    const auto &reversed = reversed_builtin_formats();
-    
-    if(reversed.find(format_string) != reversed.end())
+    if(id_ == -1)
     {
-        format_index_ = reversed.at(format_string);
-        
-        for(const auto &pair : format_strings())
+        for(const auto &pair : builtin_formats())
         {
             if(pair.second == format_string)
             {
-                format_code_ = pair.first;
+                id_ = pair.first;
                 break;
             }
         }
     }
 }
 
-void number_format::set_format_code(xlnt::number_format::format format_code)
-{
-    format_code_ = format_code;
-    format_string_ = format_strings().at(format_code);
-    
-    try
-    {
-        format_index_ = reversed_builtin_formats().at(format_string_);
-    }
-    catch(std::out_of_range)
-    {
-        format_index_ = -1;
-    }
-}
-
 } // namespace xlnt
diff --git a/source/styles/protection.cpp b/source/styles/protection.cpp
index 4447b9e2..c753388b 100644
--- a/source/styles/protection.cpp
+++ b/source/styles/protection.cpp
@@ -7,7 +7,7 @@ protection::protection() : protection(type::unprotected)
     
 }
 
-protection::protection(type t) : locked_(t), hidden_(type::inherit)
+protection::protection(type t) : locked_(t), hidden_(type::unprotected)
 {
     
 }
diff --git a/source/styles/style.cpp b/source/styles/style.cpp
index 8ebed64a..22395c2f 100644
--- a/source/styles/style.cpp
+++ b/source/styles/style.cpp
@@ -18,28 +18,91 @@ void hash_combine(std::size_t& seed, const T& v)
 
 namespace xlnt {
 
-style::style()
+const color color::black = color(color::type::indexed, 0);
+const color color::white = color(color::type::indexed, 0);
+
+style::style() :
+    id_(0),
+    alignment_apply_(false),
+    border_apply_(false),
+    border_id_(0),
+    fill_apply_(false),
+    fill_id_(0),
+    font_apply_(false),
+    font_id_(0),
+    number_format_apply_(false),
+    number_format_id_(0),
+    protection_apply_(false),
+    pivot_button_(false),
+    quote_prefix_(false)
 {
 }
 
+style::style(const style &other) :
+    id_(other.id_),
+    alignment_(other.alignment_),
+    alignment_apply_(other.alignment_apply_),
+    border_(other.border_),
+    border_apply_(other.border_apply_),
+    border_id_(other.border_id_),
+    fill_(other.fill_),
+    fill_apply_(other.fill_apply_),
+    fill_id_(other.fill_id_),
+    font_(other.font_),
+    font_apply_(other.font_apply_),
+    font_id_(other.font_id_),
+    number_format_(other.number_format_),
+    number_format_apply_(other.number_format_apply_),
+    number_format_id_(other.number_format_id_),
+    protection_(other.protection_),
+    protection_apply_(other.protection_apply_),
+    pivot_button_(other.pivot_button_),
+    quote_prefix_(other.quote_prefix_)
+{
+}
+
+style &style::operator=(const style &other)
+{
+    id_ = other.id_;
+    alignment_ = other.alignment_;
+    alignment_apply_ = other.alignment_apply_;
+    border_ = other.border_;
+    border_apply_ = other.border_apply_;
+    border_id_ = other.border_id_;
+    fill_ = other.fill_;
+    fill_apply_ = other.fill_apply_;
+    fill_id_ = other.fill_id_;
+    font_ = other.font_;
+    font_apply_ = other.font_apply_;
+    font_id_ = other.font_id_;
+    number_format_ = other.number_format_;
+    number_format_apply_ = other.number_format_apply_;
+    number_format_id_ = other.number_format_id_;
+    protection_ = other.protection_;
+    protection_apply_ = other.protection_apply_;
+    pivot_button_ = other.pivot_button_;
+    quote_prefix_ = other.quote_prefix_;
+    
+    return *this;
+}
+
 std::size_t style::hash() const
 {
-    /*
-    std::size_t seed = 100;
-    std::hash<std::string> string_hash;
-    auto font_ = get_font();
-    hash_combine(seed, string_hash(font_.name_));
-    hash_combine(seed, font_.size_);
-    hash_combine(seed, static_cast<std::size_t>(font_.underline_));
-    std::size_t bools = font_.bold_;
-    bools = bools << 1 & font_.italic_;
-    bools = bools << 1 & font_.strikethrough_;
-    bools = bools << 1 & font_.superscript_;
-    bools = bools << 1 & font_.subscript_;
-    hash_combine(seed, bools);
-     */
-    std::size_t seed = 100;
-    hash_combine(seed, number_format_.hash());
+    std::size_t seed = 0;
+    if(alignment_apply_) hash_combine(seed, alignment_apply_);
+    hash_combine(seed, alignment_.hash());
+    hash_combine(seed, border_apply_);
+    hash_combine(seed, border_id_);
+    hash_combine(seed, font_apply_);
+    hash_combine(seed, font_id_);
+    hash_combine(seed, fill_apply_);
+    hash_combine(seed, fill_id_);
+    hash_combine(seed, number_format_apply_);
+    hash_combine(seed, number_format_id_);
+    hash_combine(seed, protection_apply_);
+    if(protection_apply_) hash_combine(seed, get_protection().hash());
+//    hash_combine(seed, pivot_button_);
+//    hash_combine(seed, quote_prefix_);
     
     return seed;
 }
diff --git a/source/workbook/workbook.cpp b/source/workbook/workbook.cpp
index e49096fb..b5d8b591 100644
--- a/source/workbook/workbook.cpp
+++ b/source/workbook/workbook.cpp
@@ -12,9 +12,7 @@
 #include <xlnt/common/relationship.hpp>
 #include <xlnt/common/zip_file.hpp>
 #include <xlnt/drawing/drawing.hpp>
-#include <xlnt/reader/shared_strings_reader.hpp>
-#include <xlnt/reader/workbook_reader.hpp>
-#include <xlnt/reader/worksheet_reader.hpp>
+#include <xlnt/reader/excel_reader.hpp>
 #include <xlnt/styles/alignment.hpp>
 #include <xlnt/styles/border.hpp>
 #include <xlnt/styles/fill.hpp>
@@ -26,10 +24,7 @@
 #include <xlnt/workbook/workbook.hpp>
 #include <xlnt/worksheet/range.hpp>
 #include <xlnt/worksheet/worksheet.hpp>
-#include <xlnt/writer/style_writer.hpp>
-#include <xlnt/writer/manifest_writer.hpp>
-#include <xlnt/writer/worksheet_writer.hpp>
-#include <xlnt/writer/workbook_writer.hpp>
+#include <xlnt/writer/excel_writer.hpp>
 
 #include "detail/cell_impl.hpp"
 #include "detail/include_pugixml.hpp"
@@ -70,7 +65,7 @@ void hash_combine(std::size_t& seed, const T& v)
 namespace xlnt {
 namespace detail {
 
-workbook_impl::workbook_impl() : active_sheet_index_(0), guess_types_(false), data_only_(false)
+workbook_impl::workbook_impl() : active_sheet_index_(0), guess_types_(false), data_only_(false), next_custom_format_id_(164)
 {
 }
 
@@ -277,122 +272,24 @@ range workbook::get_named_range(const std::string &name)
     throw std::runtime_error("named range not found");
 }
 
-bool workbook::load(const std::istream &stream)
+bool workbook::load(std::istream &stream)
 {
-    std::string temp_file = create_temporary_filename();
-    
-    std::ofstream tmp;
-    
-    tmp.open(temp_file, std::ios::out | std::ios::binary);
-    tmp << stream.rdbuf();
-    tmp.close();
-    
-    load(temp_file);
-    
-    std::remove(temp_file.c_str());
+    *this = excel_reader::load_workbook(stream);
     
     return true;
 }
     
 bool workbook::load(const std::vector<unsigned char> &data)
 {
-    xlnt::zip_file archive;
-    archive.load(data);
-    return load(archive);
+    *this = excel_reader::load_workbook(data);
+    
+    return true;
 }
 
 bool workbook::load(const std::string &filename)
 {
-    zip_file f;
-
-    try
-    {
-        f.load(filename);
-    }
-    catch(std::exception e)
-    {
-        throw invalid_file_exception(filename);
-    }
+    *this = excel_reader::load_workbook(filename);
     
-    return load(f);
-}
-    
-bool workbook::load(xlnt::zip_file &archive)
-{
-    auto content_types = read_content_types(archive);
-    auto type = determine_document_type(content_types);
-
-    if(type != "excel")
-    {
-        throw invalid_file_exception("");
-    }
-    
-    clear();
-    
-    auto workbook_relationships = read_relationships(archive, "xl/workbook.xml");
-
-    for(auto relationship : workbook_relationships)
-    {
-		create_relationship(relationship.get_id(), relationship.get_target_uri(), relationship.get_type());
-    }
-    
-    pugi::xml_document doc;
-    doc.load(archive.read("xl/workbook.xml").c_str());
-    
-    auto root_node = doc.child("workbook");
-    
-    auto workbook_pr_node = root_node.child("workbookPr");
-    get_properties().excel_base_date = (workbook_pr_node.attribute("date1904") != nullptr && workbook_pr_node.attribute("date1904").as_int() != 0) ? calendar::mac_1904 : calendar::windows_1900;
-    
-    auto sheets_node = root_node.child("sheets");
-    
-    std::vector<std::string> shared_strings;
-    
-    if(archive.has_file("xl/sharedStrings.xml"))
-    {
-        shared_strings = read_shared_strings(archive.read("xl/sharedStrings.xml"));
-    }
-
-    std::vector<int> number_format_ids;
-    std::unordered_map<int, std::string> custom_number_formats;
-    
-    if(archive.has_file("xl/styles.xml"))
-    {
-        pugi::xml_document styles_doc;
-        styles_doc.load(archive.read("xl/styles.xml").c_str());
-        auto stylesheet_node = styles_doc.child("styleSheet");
-        auto cell_xfs_node = stylesheet_node.child("cellXfs");
-
-        for(auto xf_node : cell_xfs_node.children("xf"))
-        {
-            number_format_ids.push_back(xf_node.attribute("numFmtId").as_int());
-        }
-        
-        auto num_fmts_node = stylesheet_node.child("numFmts");
-        
-        for(auto num_fmt_node : num_fmts_node.children("numFmt"))
-        {
-            custom_number_formats[num_fmt_node.attribute("numFmtId").as_int()] = num_fmt_node.attribute("formatCode").as_string();
-        }
-    }
-    
-    for(auto sheet_node : sheets_node.children("sheet"))
-    {
-		std::string rel_id = sheet_node.attribute("r:id").as_string();
-		auto rel = std::find_if(d_->relationships_.begin(), d_->relationships_.end(),
-			[&](relationship &r) { return r.get_id() == rel_id; });
-
-		if (rel == d_->relationships_.end())
-		{
-			throw std::runtime_error("relationship not found");
-		}
-
-        auto ws = create_sheet(sheet_node.attribute("name").as_string(), *rel);
-        auto sheet_filename = rel->get_target_uri();
-
-        read_worksheet(ws, archive.read(sheet_filename).c_str(), shared_strings, number_format_ids, custom_number_formats);
-    }
-
     return true;
 }
 
@@ -671,36 +568,26 @@ void workbook::set_data_only(bool data_only)
     d_->data_only_ = data_only;
 }
 
-void workbook::add_border(xlnt::border /*b*/)
+void workbook::add_border(const xlnt::border &border_)
 {
-    
+    d_->borders_.push_back(border_);
 }
 
-void workbook::add_alignment(xlnt::alignment /*a*/)
+void workbook::add_fill(const fill &fill_)
 {
-    
+    d_->fills_.push_back(fill_);
 }
 
-void workbook::add_protection(xlnt::protection /*p*/)
+void workbook::add_font(const font &font_)
 {
-    
+    d_->fonts_.push_back(font_);
 }
 
-void workbook::add_number_format(const std::string &/*format*/)
+void workbook::add_number_format(const number_format &number_format_)
 {
-    
+    d_->number_formats_.push_back(number_format_);
 }
-
-void workbook::add_fill(xlnt::fill &/*f*/)
-{
     
-}
-
-void workbook::add_font(xlnt::font /*f*/)
-{
-    
-}
-
 void workbook::set_code_name(const std::string &/*code_name*/)
 {
     
@@ -731,19 +618,42 @@ std::vector<named_range> workbook::get_named_ranges() const
     return named_ranges;
 }
 
-std::size_t workbook::add_style(xlnt::style style_)
+std::size_t workbook::add_style(const xlnt::style &style_)
 {
-    return 1;
+    for(std::size_t i = 0; i < d_->styles_.size(); i++)
+    {
+        if(d_->styles_[i] == style_)
+        {
+            return i;
+        }
+    }
+    
+    d_->styles_.push_back(style_);
+    
+    return d_->styles_.size() - 1;
 }
 
 const number_format &workbook::get_number_format(std::size_t style_id) const
 {
-    return d_->number_formats_[d_->styles_[style_id].number_format_index_];
+    auto number_format_id = d_->styles_[style_id].number_format_id_;
+    
+    for(const auto &number_format_ : d_->number_formats_)
+    {
+        if(number_format_.get_id() == number_format_id)
+        {
+            return number_format_;
+        }
+    }
+    
+    auto nf = number_format::from_builtin_id(static_cast<int>(number_format_id));
+    d_->number_formats_.push_back(nf);
+    
+    return d_->number_formats_.back();
 }
 
 const font &workbook::get_font(std::size_t style_id) const
 {
-    return d_->fonts_[d_->styles_[style_id].font_index_];
+    return d_->fonts_[d_->styles_[style_id].font_id_];
 }
 
 std::size_t workbook::set_font(const font &font_, std::size_t style_id)
@@ -763,14 +673,14 @@ std::size_t workbook::set_font(const font &font_, std::size_t style_id)
     
     auto existing_style = d_->styles_[style_id];
     
-    if(font_index == existing_style.font_index_)
+    if(font_index == existing_style.font_id_)
     {
         // no change
         return style_id;
     }
     
     auto new_style = existing_style;
-    new_style.font_index_ = font_index;
+    new_style.font_id_ = font_index;
     
     auto style_match = std::find(d_->styles_.begin(), d_->styles_.end(), new_style);
 
@@ -786,7 +696,7 @@ std::size_t workbook::set_font(const font &font_, std::size_t style_id)
 
 const fill &workbook::get_fill(std::size_t style_id) const
 {
-    return d_->fills_[d_->styles_[style_id].fill_index_];
+    return d_->fills_[d_->styles_[style_id].fill_id_];
 }
 
 std::size_t workbook::set_fill(const fill &fill_, std::size_t style_id)
@@ -796,7 +706,7 @@ std::size_t workbook::set_fill(const fill &fill_, std::size_t style_id)
 
 const border &workbook::get_border(std::size_t style_id) const
 {
-    return d_->borders_[d_->styles_[style_id].border_index_];
+    return d_->borders_[d_->styles_[style_id].border_id_];
 }
 
 std::size_t workbook::set_border(const border &border_, std::size_t style_id)
@@ -806,7 +716,7 @@ std::size_t workbook::set_border(const border &border_, std::size_t style_id)
 
 const alignment &workbook::get_alignment(std::size_t style_id) const
 {
-    return d_->alignments_[d_->styles_[style_id].alignment_index_];
+    return d_->styles_[style_id].alignment_;
 }
 
 std::size_t workbook::set_alignment(const alignment &alignment_, std::size_t style_id)
@@ -816,7 +726,7 @@ std::size_t workbook::set_alignment(const alignment &alignment_, std::size_t sty
 
 const protection &workbook::get_protection(std::size_t style_id) const
 {
-    return d_->protections_[d_->styles_[style_id].number_format_index_];
+    return d_->styles_[style_id].protection_;
 }
 
 std::size_t workbook::set_protection(const protection &protection_, std::size_t style_id)
@@ -837,54 +747,84 @@ bool workbook::get_quote_prefix(std::size_t style_id) const
 std::size_t workbook::set_number_format(const xlnt::number_format &format, std::size_t style_id)
 {
     auto match = std::find(d_->number_formats_.begin(), d_->number_formats_.end(), format);
-    auto format_index = 0;
+    std::size_t format_id = 0;
     
     if(match == d_->number_formats_.end())
     {
         d_->number_formats_.push_back(format);
-        format_index = d_->number_formats_.size() - 1;
+        
+        if(format.get_id() == -1)
+        {
+            d_->number_formats_.back().set_id(d_->next_custom_format_id_++);
+        }
+        
+        format_id = d_->number_formats_.back().get_id();
     }
     else
     {
-        format_index = match - d_->number_formats_.begin();
+        format_id = match->get_id();
     }
     
     if(d_->styles_.empty())
     {
         style new_style;
-        new_style.style_index_ = 0;
-        new_style.alignment_index_ = 0;
-        new_style.border_index_ = 0;
-        new_style.fill_index_ = 0;
-        new_style.font_index_ = 0;
-        new_style.number_format_index_ = format_index;
-        new_style.protection_index_ = 0;
+        
+        new_style.id_ = 0;
+        new_style.border_id_ = 0;
+        new_style.fill_id_ = 0;
+        new_style.font_id_ = 0;
+        new_style.number_format_id_ = format_id;
+        new_style.number_format_apply_ = true;
+        
+        if(d_->borders_.empty())
+        {
+            d_->borders_.push_back(new_style.get_border());
+        }
+        
+        if(d_->fills_.empty())
+        {
+            d_->fills_.push_back(new_style.get_fill());
+        }
+        
+        if(d_->fonts_.empty())
+        {
+            d_->fonts_.push_back(new_style.get_font());
+        }
+        
         d_->styles_.push_back(new_style);
+        
         return 0;
     }
     
+    // If the style is unchanged, just return it.
     auto existing_style = d_->styles_[style_id];
+    existing_style.number_format_apply_ = true;
     
-    if(format_index == existing_style.number_format_index_)
+    if(format_id == existing_style.number_format_id_)
     {
         // no change
         return style_id;
     }
     
+    // Make a new style with this format.
     auto new_style = existing_style;
-    new_style.number_format_index_ = format_index;
+    
+    new_style.number_format_id_ = format_id;
     new_style.number_format_ = format;
     
+    // Check if the new style is already applied to a different cell. If so, reuse it.
     auto style_match = std::find(d_->styles_.begin(), d_->styles_.end(), new_style);
     
     if(style_match != d_->styles_.end())
     {
-        return style_match - d_->styles_.begin();
+        return style_match->get_id();
     }
     
+    // No match found, so add it.
+    new_style.id_ = d_->styles_.size();
     d_->styles_.push_back(new_style);
     
-    return d_->styles_.size() - 1;
+    return new_style.id_;
 }
     
 std::vector<style> workbook::get_styles() const
@@ -901,5 +841,15 @@ std::vector<font> workbook::get_fonts() const
 {
     return d_->fonts_;
 }
+
+std::vector<border> workbook::get_borders() const
+{
+    return d_->borders_;
+}
+
+std::vector<fill> workbook::get_fills() const
+{
+    return d_->fills_;
+}
     
 } // namespace xlnt
diff --git a/source/worksheet/worksheet_reader.cpp b/source/worksheet/worksheet_reader.cpp
index b5be66c6..fc950b51 100644
--- a/source/worksheet/worksheet_reader.cpp
+++ b/source/worksheet/worksheet_reader.cpp
@@ -1,5 +1,6 @@
 #include <xlnt/cell/cell.hpp>
 #include <xlnt/cell/cell_reference.hpp>
+#include <xlnt/common/zip_file.hpp>
 #include <xlnt/reader/worksheet_reader.hpp>
 #include <xlnt/styles/number_format.hpp>
 #include <xlnt/workbook/workbook.hpp>
@@ -10,8 +11,17 @@
 
 namespace {
     
-void read_worksheet_common(xlnt::worksheet ws, const pugi::xml_node &root_node, const std::vector<std::string> &string_table, const std::vector<int> &number_format_ids, const std::unordered_map<int, std::string> &custom_number_formats)
-{
+} // namespace
+
+namespace xlnt {
+
+void read_worksheet(worksheet ws, zip_file &archive, const relationship &rel, const std::vector<std::string> &string_table)
+{    
+    pugi::xml_document doc;
+    doc.load(archive.read(rel.get_target_uri()).c_str());
+    
+    auto root_node = doc.child("worksheet");
+    
     auto dimension_node = root_node.child("dimension");
     std::string dimension = dimension_node.attribute("ref").as_string();
     auto full_range = xlnt::range_reference(dimension);
@@ -62,85 +72,59 @@ void read_worksheet_common(xlnt::worksheet ws, const pugi::xml_node &root_node,
             if(cell_node != nullptr)
             {
                 bool has_value = cell_node.child("v") != nullptr;
-                std::string value_string = cell_node.child("v").text().as_string();
+                std::string value_string = has_value ? cell_node.child("v").text().as_string() : "";
                 
                 bool has_type = cell_node.attribute("t") != nullptr;
-                std::string type = cell_node.attribute("t").as_string();
+                std::string type = has_type ? cell_node.attribute("t").as_string() : "";
                 
                 bool has_style = cell_node.attribute("s") != nullptr;
-                std::string style = cell_node.attribute("s").as_string();
+                int style_id = has_style ? cell_node.attribute("s").as_int() : 0;
                 
                 bool has_formula = cell_node.child("f") != nullptr;
-                bool shared_formula = has_formula && cell_node.child("f").attribute("t") != nullptr && std::string(cell_node.child("f").attribute("t").as_string()) == "shared";
+                bool has_shared_formula = has_formula && cell_node.child("f").attribute("t") != nullptr && std::string(cell_node.child("f").attribute("t").as_string()) == "shared";
                 
-                if(has_formula && !shared_formula && !ws.get_parent().get_data_only())
+                auto cell = ws.get_cell(address);
+                
+                if(has_formula && !has_shared_formula && !ws.get_parent().get_data_only())
                 {
                     std::string formula = cell_node.child("f").text().as_string();
-                    ws.get_cell(address).set_formula(formula);
+                    cell.set_formula(formula);
                 }
                 
                 if(has_type && type == "inlineStr") // inline string
                 {
                     std::string inline_string = cell_node.child("is").child("t").text().as_string();
-                    ws.get_cell(address).set_value(inline_string);
+                    cell.set_value(inline_string);
                 }
                 else if(has_type && type == "s" && !has_formula) // shared string
                 {
-                    auto shared_string_index = std::stoll(value_string);
-                    auto shared_string = string_table.at(static_cast<std::size_t>(shared_string_index));
-                    ws.get_cell(address).set_value(shared_string);
+                    auto shared_string_index = std::stoull(value_string);
+                    auto shared_string = string_table.at(shared_string_index);
+                    cell.set_value(shared_string);
                 }
                 else if(has_type && type == "b") // boolean
                 {
-                    ws.get_cell(address).set_value(value_string != "0");
+                    cell.set_value(value_string != "0");
                 }
                 else if(has_type && type == "str")
                 {
-                    ws.get_cell(address).set_value(value_string);
+                    cell.set_value(value_string);
                 }
                 else if(has_value)
                 {
-                    try
+                    if(!value_string.empty() && value_string[0] == '#')
                     {
-                        ws.get_cell(address).set_value(std::stold(value_string));
+                        cell.set_error(value_string);
                     }
-                    catch(std::invalid_argument)
+                    else
                     {
-                        ws.get_cell(address).set_value(value_string);
+                        cell.set_value(std::stold(value_string));
                     }
                 }
                 
                 if(has_style)
                 {
-                    auto style_index = static_cast<std::size_t>(std::stoll(style));
-                    
-                    if(number_format_ids.size() > style_index)
-                    {
-                        auto number_format_id = number_format_ids.at(style_index);
-                        auto format = xlnt::number_format::lookup_format(number_format_id);
-                        
-                        if(format == xlnt::number_format::format::unknown)
-                        {
-                            auto match = custom_number_formats.find(number_format_id);
-                            
-                            if(match != custom_number_formats.end())
-                            {
-                                xlnt::number_format nf(match->second);
-                                auto cell = ws.get_cell(address);
-                                cell.set_number_format(nf);
-                            }
-                        }
-                        else
-                        {
-                            xlnt::number_format nf(format);
-                            auto cell = ws.get_cell(address);
-                            cell.set_number_format(nf);
-                        }
-                    }
-                }
-                else
-                {
-                    ws.get_cell(address).set_number_format(xlnt::number_format(xlnt::number_format::format::general));
+                    cell.set_style_id(style_id);
                 }
             }
         }
@@ -155,32 +139,4 @@ void read_worksheet_common(xlnt::worksheet ws, const pugi::xml_node &root_node,
     }
 }
     
-} // namespace
-
-namespace xlnt {
-
-void read_worksheet(worksheet ws, const std::string &xml_string, const std::vector<std::string> &string_table, const std::vector<int> &number_format_ids, const std::unordered_map<int, std::string> &custom_number_formats)
-{
-    pugi::xml_document doc;
-    doc.load(xml_string.c_str());
-    read_worksheet_common(ws, doc.child("worksheet"), string_table, number_format_ids, custom_number_formats);
-}
-
-void read_worksheet(worksheet ws, std::istream &stream, const std::vector<std::string> &string_table, const std::vector<int> &number_format_ids, const std::unordered_map<int, std::string> &custom_number_formats)
-{
-    pugi::xml_document doc;
-    doc.load(stream);
-    read_worksheet_common(ws, doc.child("worksheet"), string_table, number_format_ids, custom_number_formats);
-}
-
-worksheet read_worksheet(std::istream &handle, xlnt::workbook &wb, const std::string &title, const std::vector<std::string> &string_table, const std::unordered_map<int, std::string> &custom_number_formats)
-{
-    auto ws = wb.create_sheet();
-    ws.set_title(title);
-    pugi::xml_document doc;
-    doc.load(handle);
-    read_worksheet_common(ws, doc.child("worksheet"), string_table, {}, custom_number_formats);
-    return ws;
-}
-    
 } // namespace xlnt
diff --git a/source/writer/excel_writer.cpp b/source/writer/excel_writer.cpp
new file mode 100644
index 00000000..a38e5a69
--- /dev/null
+++ b/source/writer/excel_writer.cpp
@@ -0,0 +1,145 @@
+#include <unordered_set>
+
+#include <xlnt/cell/cell.hpp>
+#include <xlnt/cell/cell_reference.hpp>
+#include <xlnt/common/zip_file.hpp>
+#include <xlnt/workbook/workbook.hpp>
+#include <xlnt/worksheet/range.hpp>
+#include <xlnt/worksheet/range_reference.hpp>
+#include <xlnt/worksheet/worksheet.hpp>
+#include <xlnt/writer/excel_writer.hpp>
+#include <xlnt/writer/manifest_writer.hpp>
+#include <xlnt/writer/workbook_writer.hpp>
+#include <xlnt/writer/worksheet_writer.hpp>
+
+#include "detail/constants.hpp"
+
+namespace {
+
+std::vector<std::string> extract_all_strings(xlnt::workbook &wb)
+{
+    std::unordered_set<std::string> strings;
+    
+    for(auto ws : wb)
+    {
+        for(auto row : ws.rows())
+        {
+            for(auto cell : row)
+            {
+                if(cell.get_data_type() == xlnt::cell::type::string)
+                {
+                    strings.insert(cell.get_value<std::string>());
+                }
+            }
+        }
+    }
+    
+    return std::vector<std::string>(strings.begin(), strings.end());
+}
+
+} // namespace
+
+namespace xlnt {
+
+excel_writer::excel_writer(workbook &wb) : wb_(wb)
+{
+}
+
+void excel_writer::save(const std::string &filename, bool as_template)
+{
+    zip_file archive;
+    write_data(archive, as_template);
+    archive.save(filename);
+}
+
+void excel_writer::write_data(zip_file &archive, bool as_template)
+{
+    archive.writestr(constants::ArcRootRels, write_root_rels(wb_));
+    archive.writestr(constants::ArcWorkbookRels, write_workbook_rels(wb_));
+    archive.writestr(constants::ArcApp, write_properties_app(wb_));
+    archive.writestr(constants::ArcCore, write_properties_core(wb_.get_properties()));
+    
+    if(wb_.has_loaded_theme())
+    {
+        archive.writestr(constants::ArcTheme, wb_.get_loaded_theme());
+    }
+    else
+    {
+        archive.writestr(constants::ArcTheme, write_theme());
+    }
+    
+    archive.writestr(constants::ArcWorkbook, write_workbook(wb_));
+    
+    auto shared_strings = extract_all_strings(wb_);
+    
+    write_charts(archive);
+    write_images(archive);
+    write_shared_strings(archive, shared_strings);
+    write_worksheets(archive, shared_strings);
+    write_chartsheets(archive);
+    write_external_links(archive);
+    
+    style_writer style_writer_(wb_);
+    archive.writestr(constants::ArcStyles, style_writer_.write_table());
+    
+    auto manifest = write_content_types(wb_, as_template);
+    archive.writestr(constants::ArcContentTypes, manifest);
+}
+    
+void excel_writer::write_shared_strings(xlnt::zip_file &archive, const std::vector<std::string> &shared_strings)
+{
+    archive.writestr(constants::ArcSharedString, ::xlnt::write_shared_strings(shared_strings));
+}
+
+void excel_writer::write_images(zip_file &/*archive*/)
+{
+    
+}
+
+void excel_writer::write_charts(zip_file &/*archive*/)
+{
+    
+}
+
+void excel_writer::write_chartsheets(zip_file &/*archive*/)
+{
+    
+}
+
+void excel_writer::write_worksheets(zip_file &archive, const std::vector<std::string> &shared_strings)
+{
+    for(auto relationship : wb_.get_relationships())
+    {
+        if(relationship.get_type() == relationship::type::worksheet)
+        {
+            auto sheet_index = workbook::index_from_ws_filename(relationship.get_target_uri());
+            auto ws = wb_.get_sheet_by_index(sheet_index);
+            archive.writestr(relationship.get_target_uri(), write_worksheet(ws, shared_strings));
+        }
+    }
+}
+
+void excel_writer::write_external_links(zip_file &/*archive*/)
+{
+    
+}
+
+bool save_workbook(workbook &wb, const std::string &filename, bool as_template)
+{
+    excel_writer writer(wb);
+    writer.save(filename, as_template);
+    return true;
+}
+
+std::vector<std::uint8_t> save_virtual_workbook(xlnt::workbook &wb, bool as_template)
+{
+    zip_file archive;
+    excel_writer writer(wb);
+    writer.write_data(archive, as_template);
+    std::vector<std::uint8_t> buffer;
+    archive.save(buffer);
+    
+    return buffer;
+}
+
+} // namespace xlnt
diff --git a/source/writer/style_writer.cpp b/source/writer/style_writer.cpp
index df060642..de2193b1 100644
--- a/source/writer/style_writer.cpp
+++ b/source/writer/style_writer.cpp
@@ -33,21 +33,10 @@ std::string style_writer::write_table() const
     auto num_fmts = wb_.get_number_formats();
     num_fmts_node.append_attribute("count").set_value(static_cast<int>(num_fmts.size()));
     
-    int custom_index = 164;
-    
     for(auto &num_fmt : num_fmts)
     {
         auto num_fmt_node = num_fmts_node.append_child("numFmt");
-        
-        if(num_fmt.get_format_code() == number_format::format::unknown)
-        {
-            num_fmt_node.append_attribute("numFmtId").set_value(custom_index++);
-        }
-        else
-        {
-            num_fmt_node.append_attribute("numFmtId").set_value(num_fmt.get_format_index());
-        }
-        
+        num_fmt_node.append_attribute("numFmtId").set_value(num_fmt.get_id());
         num_fmt_node.append_attribute("formatCode").set_value(num_fmt.get_format_string().c_str());
     }
 
@@ -63,16 +52,35 @@ std::string style_writer::write_table() const
     for(auto &f : fonts)
     {
         auto font_node = fonts_node.append_child("font");
+        
         auto size_node = font_node.append_child("sz");
         size_node.append_attribute("val").set_value(f.get_size());
+        
         auto color_node = font_node.append_child("color");
-        color_node.append_attribute("theme").set_value(1);
+        
+        if(f.get_color().get_type() == color::type::indexed)
+        {
+            color_node.append_attribute("indexed").set_value(static_cast<unsigned int>(f.get_color().get_index()));
+        }
+        else if(f.get_color().get_type() == color::type::theme)
+        {
+            color_node.append_attribute("theme").set_value(static_cast<unsigned int>(f.get_color().get_theme()));
+        }
+        
         auto name_node = font_node.append_child("name");
         name_node.append_attribute("val").set_value(f.get_name().c_str());
-        auto family_node = font_node.append_child("family");
-        family_node.append_attribute("val").set_value(2);
-        auto scheme_node = font_node.append_child("scheme");
-        scheme_node.append_attribute("val").set_value("minor");
+        
+        if(f.has_family())
+        {
+            auto family_node = font_node.append_child("family");
+            family_node.append_attribute("val").set_value(2);
+        }
+        
+        if(f.has_scheme())
+        {
+            auto scheme_node = font_node.append_child("scheme");
+            scheme_node.append_attribute("val").set_value("minor");
+        }
         
         if(f.is_bold())
         {
@@ -82,52 +90,322 @@ std::string style_writer::write_table() const
     }
 
     auto fills_node = style_sheet_node.append_child("fills");
-    fills_node.append_attribute("count").set_value(2);
-    fills_node.append_child("fill").append_child("patternFill").append_attribute("patternType").set_value("none");
-    fills_node.append_child("fill").append_child("patternFill").append_attribute("patternType").set_value("gray125");
+    const auto &fills = wb_.get_fills();
+    fills_node.append_attribute("count").set_value(static_cast<unsigned int>(fills.size()));
+    
+    for(auto &fill_ : fills)
+    {
+        auto fill_node = fills_node.append_child("fill");
+        
+        if(fill_.get_type() == fill::type::pattern)
+        {
+            auto pattern_fill_node = fill_node.append_child("patternFill");
+            auto type_string = fill_.get_pattern_type_string();
+            pattern_fill_node.append_attribute("patternType").set_value(type_string.c_str());
+            
+            if(fill_.has_foreground_color())
+            {
+                auto fg_color_node = pattern_fill_node.append_child("fgColor");
+                
+                switch(fill_.get_foreground_color().get_type())
+                {
+                    case color::type::auto_: fg_color_node.append_attribute("auto").set_value(fill_.get_foreground_color().get_auto()); break;
+                    case color::type::theme: fg_color_node.append_attribute("theme").set_value(fill_.get_foreground_color().get_theme()); break;
+                    case color::type::indexed: fg_color_node.append_attribute("indexed").set_value(fill_.get_foreground_color().get_index()); break;
+                    default: throw std::runtime_error("bad type");
+                }
+            }
+            
+            if(fill_.has_background_color())
+            {
+                auto bg_color_node = pattern_fill_node.append_child("bgColor");
+                
+                switch(fill_.get_background_color().get_type())
+                {
+                    case color::type::auto_: bg_color_node.append_attribute("auto").set_value(fill_.get_background_color().get_auto()); break;
+                    case color::type::theme: bg_color_node.append_attribute("theme").set_value(fill_.get_background_color().get_theme()); break;
+                    case color::type::indexed: bg_color_node.append_attribute("indexed").set_value(fill_.get_background_color().get_index()); break;
+                    default: throw std::runtime_error("bad type");
+                }
+            }
+        }
+    }
 
     auto borders_node = style_sheet_node.append_child("borders");
-    borders_node.append_attribute("count").set_value(1);
-    auto border_node = borders_node.append_child("border");
-    border_node.append_child("left");
-    border_node.append_child("right");
-    border_node.append_child("top");
-    border_node.append_child("bottom");
-    border_node.append_child("diagonal");
+    const auto &borders = wb_.get_borders();
+    borders_node.append_attribute("count").set_value(static_cast<unsigned int>(borders.size()));
+    
+    for(const auto &border_ : borders)
+    {
+        auto border_node = borders_node.append_child("border");
+        
+        if(border_.left_assigned)
+        {
+            auto left_node = border_node.append_child("left");
+            
+            if(border_.left.is_style_assigned())
+            {
+                auto style_attribute = left_node.append_attribute("style");
+                
+                switch(border_.left.get_style())
+                {
+                    case border_style::none: style_attribute.set_value("none"); break;
+                    case border_style::thin: style_attribute.set_value("thin"); break;
+                    default: throw std::runtime_error("invalid style");
+                }
+            }
+            
+            if(border_.left.is_color_assigned())
+            {
+                auto color_node = left_node.append_child("color");
+                
+                if(border_.left.get_color_type() == side::color_type::indexed)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.left.get_color());
+                }
+                else if(border_.diagonal.get_color_type() == side::color_type::theme)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.left.get_color());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        
+        if(border_.right_assigned)
+        {
+            auto right_node = border_node.append_child("right");
+            
+            if(border_.right.is_style_assigned())
+            {
+                auto style_attribute = right_node.append_attribute("style");
+                
+                switch(border_.right.get_style())
+                {
+                    case border_style::none: style_attribute.set_value("none"); break;
+                    case border_style::thin: style_attribute.set_value("thin"); break;
+                    default: throw std::runtime_error("invalid style");
+                }
+            }
+            
+            if(border_.right.is_color_assigned())
+            {
+                auto color_node = right_node.append_child("color");
+                
+                if(border_.right.get_color_type() == side::color_type::indexed)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.right.get_color());
+                }
+                else if(border_.diagonal.get_color_type() == side::color_type::theme)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.right.get_color());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        
+        if(border_.top_assigned)
+        {
+            auto top_node = border_node.append_child("top");
+            
+            if(border_.top.is_style_assigned())
+            {
+                auto style_attribute = top_node.append_attribute("style");
+                
+                switch(border_.top.get_style())
+                {
+                    case border_style::none: style_attribute.set_value("none"); break;
+                    case border_style::thin: style_attribute.set_value("thin"); break;
+                    default: throw std::runtime_error("invalid style");
+                }
+            }
+            
+            if(border_.top.is_color_assigned())
+            {
+                auto color_node = top_node.append_child("color");
+                if(border_.top.get_color_type() == side::color_type::indexed)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.top.get_color());
+                }
+                else if(border_.diagonal.get_color_type() == side::color_type::theme)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.top.get_color());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        
+        if(border_.bottom_assigned)
+        {
+            auto bottom_node = border_node.append_child("bottom");
+            
+            if(border_.bottom.is_style_assigned())
+            {
+                auto style_attribute = bottom_node.append_attribute("style");
+                
+                switch(border_.bottom.get_style())
+                {
+                    case border_style::none: style_attribute.set_value("none"); break;
+                    case border_style::thin: style_attribute.set_value("thin"); break;
+                    default: throw std::runtime_error("invalid style");
+                }
+            }
+            
+            if(border_.bottom.is_color_assigned())
+            {
+                auto color_node = bottom_node.append_child("color");
+                
+                if(border_.bottom.get_color_type() == side::color_type::indexed)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.bottom.get_color());
+                }
+                else if(border_.diagonal.get_color_type() == side::color_type::theme)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.bottom.get_color());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+        
+        if(border_.diagonal_assigned)
+        {
+            auto diagonal_node = border_node.append_child("diagonal");
+            
+            if(border_.diagonal.is_style_assigned())
+            {
+                auto style_attribute = diagonal_node.append_attribute("style");
+                
+                switch(border_.diagonal.get_style())
+                {
+                    case border_style::none: style_attribute.set_value("none"); break;
+                    case border_style::thin: style_attribute.set_value("thin"); break;
+                    default: throw std::runtime_error("invalid style");
+                }
+            }
+            
+            if(border_.diagonal.is_color_assigned())
+            {
+                auto color_node = diagonal_node.append_child("color");
+                
+                if(border_.diagonal.get_color_type() == side::color_type::indexed)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.diagonal.get_color());
+                }
+                else if(border_.diagonal.get_color_type() == side::color_type::theme)
+                {
+                    color_node.append_attribute("indexed").set_value((int)border_.diagonal.get_color());
+                }
+                else
+                {
+                    throw std::runtime_error("invalid color type");
+                }
+            }
+        }
+    }
 
     auto cell_style_xfs_node = style_sheet_node.append_child("cellStyleXfs");
     cell_style_xfs_node.append_attribute("count").set_value(1);
-    auto xf_node = cell_style_xfs_node.append_child("xf");
-    xf_node.append_attribute("numFmtId").set_value(0);
-    xf_node.append_attribute("fontId").set_value(0);
-    xf_node.append_attribute("fillId").set_value(0);
-    xf_node.append_attribute("borderId").set_value(0);
+    auto style_xf_node = cell_style_xfs_node.append_child("xf");
+    style_xf_node.append_attribute("numFmtId").set_value(0);
+    style_xf_node.append_attribute("fontId").set_value(0);
+    style_xf_node.append_attribute("fillId").set_value(0);
+    style_xf_node.append_attribute("borderId").set_value(0);
     
     auto cell_xfs_node = style_sheet_node.append_child("cellXfs");
     const auto &styles = wb_.get_styles();
     cell_xfs_node.append_attribute("count").set_value(static_cast<int>(styles.size()));
     
-    custom_index = 164;
-    
     for(auto &style : styles)
     {
-        xf_node = cell_xfs_node.append_child("xf");
-        if(style.get_number_format().get_format_code() == number_format::format::unknown)
-        {
-            xf_node.append_attribute("numFmtId").set_value(custom_index++);
-        }
-        else
-        {
-            xf_node.append_attribute("numFmtId").set_value(style.get_number_format().get_format_index());
-        }
-        xf_node.append_attribute("applyNumberFormat").set_value(1);
-        xf_node.append_attribute("fontId").set_value((int)style.get_font_index());
-        xf_node.append_attribute("fillId").set_value((int)style.get_fill_index());
-        xf_node.append_attribute("borderId").set_value((int)style.get_border_index());
+        auto xf_node = cell_xfs_node.append_child("xf");
+        xf_node.append_attribute("numFmtId").set_value(style.get_number_format().get_id());
+        xf_node.append_attribute("fontId").set_value((int)style.get_font_id());
         
-        auto alignment_node = xf_node.append_child("alignment");
-        alignment_node.append_attribute("vertical").set_value("top");
-        alignment_node.append_attribute("wrapText").set_value(1);
+        if(style.fill_apply_)
+        {
+            xf_node.append_attribute("fillId").set_value((int)style.get_fill_id());
+        }
+        
+        if(style.border_apply_)
+        {
+            xf_node.append_attribute("borderId").set_value((int)style.get_border_id());
+        }
+        
+        xf_node.append_attribute("applyNumberFormat").set_value(style.number_format_apply_ ? 1 : 0);
+        xf_node.append_attribute("applyFont").set_value(style.font_apply_ ? 1 : 0);
+        xf_node.append_attribute("applyFill").set_value(style.fill_apply_ ? 1 : 0);
+        xf_node.append_attribute("applyBorder").set_value(style.border_apply_ ? 1 : 0);
+        xf_node.append_attribute("applyAlignment").set_value(style.alignment_apply_ ? 1 : 0);
+        xf_node.append_attribute("applyProtection").set_value(style.protection_apply_ ? 1 : 0);
+        
+        if(style.alignment_apply_)
+        {
+            auto alignment_node = xf_node.append_child("alignment");
+            
+            if(style.alignment_.has_vertical())
+            {
+                switch(style.alignment_.get_vertical())
+                {
+                    case alignment::vertical_alignment::bottom:
+                        alignment_node.append_attribute("vertical").set_value("bottom");
+                        break;
+                    case alignment::vertical_alignment::center:
+                        alignment_node.append_attribute("vertical").set_value("center");
+                        break;
+                    case alignment::vertical_alignment::justify:
+                        alignment_node.append_attribute("vertical").set_value("justify");
+                        break;
+                    case alignment::vertical_alignment::top:
+                        alignment_node.append_attribute("vertical").set_value("top");
+                        break;
+                    default:
+                        throw std::runtime_error("invalid alignment");
+                }
+            }
+            
+            if(style.alignment_.has_horizontal())
+            {
+                switch(style.alignment_.get_horizontal())
+                {
+                    case alignment::horizontal_alignment::center:
+                        alignment_node.append_attribute("horizontal").set_value("center");
+                        break;
+                    case alignment::horizontal_alignment::center_continuous:
+                        alignment_node.append_attribute("horizontal").set_value("center_continuous");
+                        break;
+                    case alignment::horizontal_alignment::general:
+                        alignment_node.append_attribute("horizontal").set_value("general");
+                        break;
+                    case alignment::horizontal_alignment::justify:
+                        alignment_node.append_attribute("horizontal").set_value("justify");
+                        break;
+                    case alignment::horizontal_alignment::left:
+                        alignment_node.append_attribute("horizontal").set_value("left");
+                        break;
+                    case alignment::horizontal_alignment::right:
+                        alignment_node.append_attribute("horizontal").set_value("right");
+                        break;
+                    default:
+                        throw std::runtime_error("invalid alignment");
+                }
+            }
+            
+            if(style.alignment_.get_wrap_text())
+            {
+                alignment_node.append_attribute("wrapText").set_value(1);
+            }
+        }
     }
 
     auto cell_styles_node = style_sheet_node.append_child("cellStyles");
@@ -143,6 +421,30 @@ std::string style_writer::write_table() const
     table_styles_node.append_attribute("count").set_value(0);
     table_styles_node.append_attribute("defaultTableStyle").set_value("TableStyleMedium2");
     table_styles_node.append_attribute("defaultPivotStyle").set_value("PivotStyleMedium9");
+    
+    auto colors_node = style_sheet_node.append_child("colors");
+    auto indexed_colors_node = colors_node.append_child("indexedColors");
+    
+    const std::vector<std::string> colors =
+    {
+        "ff000000",
+        "ffffffff",
+        "ffff0000",
+        "ff00ff00",
+        "ff0000ff",
+        "ffffff00",
+        "ffff00ff",
+        "ff00ffff",
+        "ff000000",
+        "ffaaaaaa",
+        "ffbdc0bf",
+        "ffdbdbdb"
+    };
+    
+    for(auto &color : colors)
+    {
+        indexed_colors_node.append_child("rgbColor").append_attribute("rgb").set_value(color.c_str());
+    }
 
     auto ext_list_node = style_sheet_node.append_child("extLst");
     auto ext_node = ext_list_node.append_child("ext");
diff --git a/source/writer/workbook_writer.cpp b/source/writer/workbook_writer.cpp
index 7531578f..86550ad8 100644
--- a/source/writer/workbook_writer.cpp
+++ b/source/writer/workbook_writer.cpp
@@ -41,121 +41,6 @@ std::string datetime_to_w3cdtf(const xlnt::datetime &dt)
 
 namespace xlnt {
 
-excel_writer::excel_writer(workbook &wb) : wb_(wb), style_writer_(wb_)
-{
-}
-
-void excel_writer::save(const std::string &filename, bool as_template)
-{
-    zip_file archive;
-    write_data(archive, as_template);
-    archive.save(filename);
-}
-
-void excel_writer::write_data(zip_file &archive, bool as_template)
-{
-    archive.writestr(constants::ArcRootRels, write_root_rels(wb_));
-    archive.writestr(constants::ArcWorkbookRels, write_workbook_rels(wb_));
-    archive.writestr(constants::ArcApp, write_properties_app(wb_));
-    archive.writestr(constants::ArcCore, write_properties_core(wb_.get_properties()));
-    
-    if(wb_.has_loaded_theme())
-    {
-        archive.writestr(constants::ArcTheme, wb_.get_loaded_theme());
-    }
-    else
-    {
-        archive.writestr(constants::ArcTheme, write_theme());
-    }
-    
-    archive.writestr(constants::ArcWorkbook, write_workbook(wb_));
-
-    /*
-    if(wb_.has_vba_archive())
-    {
-        auto &vba_archive = wb_.get_vba_archive();
-        
-        for(auto name : vba_archive.namelist())
-        {
-            for(auto s : constants::ArcVba)
-            {
-                if(match(s, name))
-                {
-                    archive.writestr(name, vba_archive.read(name));
-                    break;
-                }
-            }
-        }
-    }
-    */
-    
-    write_charts(archive);
-    write_images(archive);
-    write_string_table(archive);
-    write_worksheets(archive);
-    write_chartsheets(archive);
-    write_external_links(archive);
-    
-    archive.writestr(constants::ArcStyles, style_writer_.write_table());
-    auto manifest = write_content_types(wb_, as_template);
-    archive.writestr(constants::ArcContentTypes, manifest);
-}
-
-void excel_writer::write_string_table(zip_file &archive)
-{
-    std::set<std::string> shared_strings_set;
-    
-    for(auto ws : wb_)
-    {
-        for(auto row : ws.rows())
-        {
-            for(auto cell : row)
-            {
-                if(cell.get_data_type() == cell::type::string)
-                {
-                    shared_strings_set.insert(cell.get_value<std::string>());
-                }
-            }
-        }
-    }
-    
-    shared_strings_.assign(shared_strings_set.begin(), shared_strings_set.end());
-    archive.writestr(constants::ArcSharedString, write_shared_strings(shared_strings_));
-}
-
-void excel_writer::write_images(zip_file &/*archive*/)
-{
-    
-}
-
-void excel_writer::write_charts(zip_file &/*archive*/)
-{
-    
-}
-
-void excel_writer::write_chartsheets(zip_file &/*archive*/)
-{
-    
-}
-
-void excel_writer::write_worksheets(zip_file &archive)
-{
-    for(auto relationship : wb_.get_relationships())
-    {
-        if(relationship.get_type() == relationship::type::worksheet)
-        {
-            auto sheet_index = workbook::index_from_ws_filename(relationship.get_target_uri());
-            auto ws = wb_.get_sheet_by_index(sheet_index);
-            archive.writestr(relationship.get_target_uri(), write_worksheet(ws, shared_strings_));
-        }
-    }
-}
-
-void excel_writer::write_external_links(zip_file &/*archive*/)
-{
-    
-}
-
 std::string write_shared_strings(const std::vector<std::string> &string_table)
 {
     pugi::xml_document doc;
@@ -713,22 +598,4 @@ std::string write_defined_names(const xlnt::workbook &wb)
     return stream.str();
 }
 
-bool save_workbook(workbook &wb, const std::string &filename, bool as_template)
-{
-    excel_writer writer(wb);
-    writer.save(filename, as_template);
-    return true;
-}
-
-std::vector<std::uint8_t> save_virtual_workbook(xlnt::workbook &wb, bool as_template)
-{
-    zip_file archive;
-    excel_writer writer(wb);
-    writer.write_data(archive, as_template);
-    std::vector<std::uint8_t> buffer;
-    archive.save(buffer);
-    
-    return buffer;
-}
-
 } // namespace xlnt
diff --git a/source/writer/worksheet_writer.cpp b/source/writer/worksheet_writer.cpp
index fed936e1..4aeda798 100644
--- a/source/writer/worksheet_writer.cpp
+++ b/source/writer/worksheet_writer.cpp
@@ -264,8 +264,11 @@ std::string write_worksheet(worksheet ws, const std::vector<std::string> &string
                     }
                 }
                 
-                auto style_id = cell.get_style_id();
-                cell_node.append_attribute("s").set_value((int)style_id);
+                //if(cell.has_style())
+                {
+                    auto style_id = cell.get_style_id();
+                    cell_node.append_attribute("s").set_value((int)style_id);
+                }
             }
         }
     }
diff --git a/tests/test_cell.hpp b/tests/test_cell.hpp
index 65ad68dd..2bb33087 100644
--- a/tests/test_cell.hpp
+++ b/tests/test_cell.hpp
@@ -9,18 +9,19 @@
 #include <xlnt/cell/comment.hpp>
 #include <xlnt/common/datetime.hpp>
 #include <xlnt/common/exceptions.hpp>
-#include <xlnt/reader/workbook_reader.hpp>
 #include <xlnt/styles/alignment.hpp>
 #include <xlnt/styles/border.hpp>
 #include <xlnt/styles/font.hpp>
 #include <xlnt/styles/fill.hpp>
-#include <xlnt/styles/pattern_fill.hpp>
 #include <xlnt/styles/number_format.hpp>
 #include <xlnt/styles/protection.hpp>
 #include <xlnt/worksheet/range.hpp>
 #include <xlnt/worksheet/worksheet.hpp>
 #include <xlnt/workbook/workbook.hpp>
 
+#include <xlnt/writer/excel_writer.hpp>
+#include <xlnt/reader/excel_reader.hpp>
+
 class test_cell : public CxxTest::TestSuite
 {
 private:
@@ -32,6 +33,13 @@ public:
         wb_guess_types.set_guess_types(true);
     }
     
+    void test_debug()
+    {
+        xlnt::workbook wb;
+        wb.load("/Users/thomas/Development/xlnt/samples/sample1.xlsx");
+        wb.save("/Users/thomas/Development/xlnt/bin/sample1-out.xlsx");
+    }
+    
 	void test_infer_numeric()
 	{
 		auto ws = wb_guess_types.create_sheet();
@@ -394,14 +402,14 @@ public:
     
     void _test_fill()
     {
-        xlnt::pattern_fill fill;
-        fill.set_pattern_type("solid");
-        fill.set_foreground_color("FF0000");
+        xlnt::fill f;
+        f.set_type(xlnt::fill::type::solid);
+//        f.set_foreground_color("FF0000");
         auto ws = wb.create_sheet();
-        ws.get_parent().add_fill(fill);
+        ws.get_parent().add_fill(f);
     
         xlnt::cell cell(ws, "A1");
-        TS_ASSERT(cell.get_fill() == fill);
+        TS_ASSERT(cell.get_fill() == f);
     }
     
     void _test_border()
@@ -417,7 +425,7 @@ public:
     void _test_number_format()
     {
         auto ws = wb.create_sheet();
-        ws.get_parent().add_number_format("dd--hh--mm");
+        ws.get_parent().add_number_format(xlnt::number_format("dd--hh--mm"));
     
         xlnt::cell cell(ws, "A1");
         cell.set_number_format(xlnt::number_format("dd--hh--mm"));
@@ -439,7 +447,7 @@ public:
     void _test_protection()
     {
         xlnt::protection prot;
-        prot.set_locked(false);
+        prot.set_locked(xlnt::protection::type::protected_);
         
         auto ws = wb.create_sheet();
         ws.get_parent().add_protection(prot);
diff --git a/tests/test_read.hpp b/tests/test_read.hpp
index df5bb61d..fcb00f27 100644
--- a/tests/test_read.hpp
+++ b/tests/test_read.hpp
@@ -14,28 +14,11 @@
 class test_read : public CxxTest::TestSuite
 {
 public:
-    void test_read_standalone_worksheet()
-    {
-        auto path = PathHelper::GetDataDirectory("/reader/sheet2.xml");
-        xlnt::workbook wb;
-        xlnt::worksheet ws(wb);
-        {
-            std::ifstream handle(path);
-            ws = xlnt::read_worksheet(handle, wb, "Sheet 2", {"hello"}, {});
-        }
-        TS_ASSERT_DIFFERS(ws, nullptr);
-        if(!(ws == nullptr))
-        {
-            TS_ASSERT_EQUALS(ws.get_cell("G5").get_value<std::string>(), "hello");
-            TS_ASSERT_EQUALS(ws.get_cell("D30").get_value<int>(), 30);
-            TS_ASSERT_EQUALS(ws.get_cell("K9").get_value<double>(), 0.09);
-        }
-    }
     
     xlnt::workbook standard_workbook()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/empty.xlsx");
-        return xlnt::load_workbook(path);
+        return xlnt::excel_reader::load_workbook(path);
     }
 
     void test_read_standard_workbook()
@@ -47,7 +30,7 @@ public:
     {
         auto path = PathHelper::GetDataDirectory("/genuine/empty.xlsx");
         std::ifstream fo(path, std::ios::binary);
-        auto wb = xlnt::load_workbook(path);
+        auto wb = xlnt::excel_reader::load_workbook(path);
         TS_ASSERT_DIFFERS(standard_workbook(), nullptr);
     }
 
@@ -65,58 +48,58 @@ public:
     void test_read_nostring_workbook()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/empty-no-string.xlsx");
-        auto wb = xlnt::load_workbook(path);
+        auto wb = xlnt::excel_reader::load_workbook(path);
         TS_ASSERT_DIFFERS(standard_workbook(), nullptr);
     }
 
     void test_read_empty_file()
     {
         auto path = PathHelper::GetDataDirectory("/reader/null_file.xlsx");
-        TS_ASSERT_THROWS(xlnt::load_workbook(path), xlnt::invalid_file_exception);
+        TS_ASSERT_THROWS(xlnt::excel_reader::load_workbook(path), xlnt::invalid_file_exception);
     }
 
     void test_read_empty_archive()
     {
         auto path = PathHelper::GetDataDirectory("/reader/null_archive.xlsx");
-        TS_ASSERT_THROWS(xlnt::load_workbook(path), xlnt::invalid_file_exception);
+        TS_ASSERT_THROWS(xlnt::excel_reader::load_workbook(path), xlnt::invalid_file_exception);
     }
     
     void test_read_workbook_with_no_properties()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/empty_with_no_properties.xlsx");
-        xlnt::load_workbook(path);
+        xlnt::excel_reader::load_workbook(path);
     }
 
     xlnt::workbook workbook_with_styles()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/empty-with-styles.xlsx");
-        return xlnt::load_workbook(path);
+        return xlnt::excel_reader::load_workbook(path);
     }
 
     void test_read_workbook_with_styles_general()
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A1").get_number_format().get_format_code();
-        auto expected = xlnt::number_format::format::general;
-        TS_ASSERT_EQUALS(code, expected);
+        auto format = ws.get_cell("A1").get_number_format();
+        auto expected = xlnt::number_format::general();
+        TS_ASSERT_EQUALS(format, expected);
     }
     
     void test_read_workbook_with_styles_date()
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A2").get_number_format().get_format_code();
-        auto expected = xlnt::number_format::format::date_xlsx14;
-        TS_ASSERT_EQUALS(code, expected);
+        auto format = ws.get_cell("A2").get_number_format();
+        auto expected = xlnt::number_format::date_xlsx14();
+        TS_ASSERT_EQUALS(format, expected);
     }
     
     void test_read_workbook_with_styles_number()
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A3").get_number_format().get_format_code();
-        auto expected = xlnt::number_format::format::number_00;
+        auto code = ws.get_cell("A3").get_number_format();
+        auto expected = xlnt::number_format::number_00();
         TS_ASSERT_EQUALS(code, expected);
     }
     
@@ -124,8 +107,8 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A4").get_number_format().get_format_code();
-        auto expected = xlnt::number_format::format::date_time3;
+        auto code = ws.get_cell("A4").get_number_format();
+        auto expected = xlnt::number_format::date_time3();
         TS_ASSERT_EQUALS(code, expected);
     }
     
@@ -133,21 +116,21 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A5").get_number_format().get_format_code();
-        auto expected = xlnt::number_format::format::percentage_00;
+        auto code = ws.get_cell("A5").get_number_format();
+        auto expected = xlnt::number_format::percentage_00();
         TS_ASSERT_EQUALS(code, expected);
     }
     
     xlnt::workbook date_mac_1904()
     {
         auto path = PathHelper::GetDataDirectory("/reader/date_1904.xlsx");
-        return xlnt::load_workbook(path);
+        return xlnt::excel_reader::load_workbook(path);
     }
     
     xlnt::workbook date_std_1900()
     {
         auto path = PathHelper::GetDataDirectory("/reader/date_1900.xlsx");
-        return xlnt::load_workbook(path);
+        return xlnt::excel_reader::load_workbook(path);
     }
     
     void test_read_win_base_date()
@@ -166,14 +149,14 @@ public:
     {
         auto wb = date_std_1900();
         auto ws = wb["Sheet1"];
-        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
+        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format(), xlnt::number_format::date_xlsx14());
     }
 
     void test_read_date_style_mac()
     {
         auto wb = date_mac_1904();
         auto ws = wb["Sheet1"];
-        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
+        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format(), xlnt::number_format::date_xlsx14());
     }
 
     void test_read_compare_mac_win_dates()
@@ -190,40 +173,23 @@ public:
     
     void test_repair_central_directory()
     {
-        std::string data_a = "foobarbaz" + xlnt::CentralDirectorySignature();
+        std::string data_a = "foobarbaz" + xlnt::excel_reader::CentralDirectorySignature();
         std::string data_b = "bazbarfoo12345678901234567890";
         
-        auto f = xlnt::repair_central_directory(data_a + data_b);
+        auto f = xlnt::excel_reader::repair_central_directory(data_a + data_b);
         TS_ASSERT_EQUALS(f, data_a + data_b.substr(0, 18));
         
-        f = xlnt::repair_central_directory(data_b);
+        f = xlnt::excel_reader::repair_central_directory(data_b);
         TS_ASSERT_EQUALS(f, data_b);
     }
     
     void test_read_no_theme()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/libreoffice_nrt.xlsx");
-        auto wb = xlnt::load_workbook(path);
+        auto wb = xlnt::excel_reader::load_workbook(path);
         TS_ASSERT_DIFFERS(wb, nullptr);
     }
     
-    void test_read_cell_formulae()
-    {
-        xlnt::workbook wb;
-        auto ws = wb.get_active_sheet();
-        auto path = PathHelper::GetDataDirectory("/reader/worksheet_formula.xml");
-        std::ifstream ws_stream(path);
-        xlnt::read_worksheet(ws, ws_stream, { "string", "string2" }, {}, {});
-        
-        auto b1 = ws.get_cell("B1");
-        TS_ASSERT(b1.has_formula());
-        TS_ASSERT_EQUALS(b1.get_formula(), "CONCATENATE(A1,A2)");
-        
-        auto a6 = ws.get_cell("A6");
-        TS_ASSERT(a6.has_formula());
-        TS_ASSERT_EQUALS(a6.get_formula(), "SUM(A4:A5)");
-    }
-    
     void _test_read_complex_formulae()
     {
         /*
@@ -284,7 +250,7 @@ public:
     void test_data_only()
     {
         auto path = PathHelper::GetDataDirectory("/reader/formulae.xlsx");
-        auto wb = xlnt::load_workbook(path, false, true);
+        auto wb = xlnt::excel_reader::load_workbook(path, false, true);
         auto ws = wb.get_active_sheet();
 
         TS_ASSERT(ws.get_formula_attributes().empty());
@@ -448,7 +414,7 @@ public:
         {
             std::tie(guess, dtype) = expected;
             auto path = PathHelper::GetDataDirectory("/genuine/guess_types.xlsx");
-            auto wb = xlnt::load_workbook(path, guess);
+            auto wb = xlnt::excel_reader::load_workbook(path, guess);
             auto ws = wb.get_active_sheet();
             TS_ASSERT(ws.get_cell("D2").get_data_type() == dtype);
         }
@@ -457,7 +423,7 @@ public:
     void test_read_autofilter()
     {
         auto path = PathHelper::GetDataDirectory("/reader/bug275.xlsx");
-        auto wb = xlnt::load_workbook(path);
+        auto wb = xlnt::excel_reader::load_workbook(path);
         auto ws = wb.get_active_sheet();
         TS_ASSERT_EQUALS(ws.get_auto_filter().to_string(), "A1:B6");
     }
@@ -465,18 +431,18 @@ public:
     void test_bad_formats_xlsb()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/a.xlsb");
-        TS_ASSERT_THROWS(xlnt::load_workbook(path), xlnt::invalid_file_exception);
+        TS_ASSERT_THROWS(xlnt::excel_reader::load_workbook(path), xlnt::invalid_file_exception);
     }
     
     void test_bad_formats_xls()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/a.xls");
-        TS_ASSERT_THROWS(xlnt::load_workbook(path), xlnt::invalid_file_exception);
+        TS_ASSERT_THROWS(xlnt::excel_reader::load_workbook(path), xlnt::invalid_file_exception);
     }
     
     void test_bad_formats_no()
     {
         auto path = PathHelper::GetDataDirectory("/genuine/a.no-format");
-        TS_ASSERT_THROWS(xlnt::load_workbook(path), xlnt::invalid_file_exception);
+        TS_ASSERT_THROWS(xlnt::excel_reader::load_workbook(path), xlnt::invalid_file_exception);
     }
 };
diff --git a/tests/test_style_writer.hpp b/tests/test_style_writer.hpp
index 998847ef..9423c0b3 100644
--- a/tests/test_style_writer.hpp
+++ b/tests/test_style_writer.hpp
@@ -11,7 +11,7 @@ public:
     void test_write_number_formats()
     {
         xlnt::workbook wb;
-        wb.add_number_format("YYYY");
+        wb.add_number_format(xlnt::number_format("YYYY"));
         xlnt::style_writer writer(wb);
         auto xml = writer.write_number_formats();
         std::string expected =
diff --git a/tests/test_write.hpp b/tests/test_write.hpp
index cec30657..92718a99 100644
--- a/tests/test_write.hpp
+++ b/tests/test_write.hpp
@@ -16,7 +16,7 @@ public:
         xlnt::workbook wbk;
         wbk.get_active_sheet().get_cell("A2").set_value("xlnt");
         wbk.get_active_sheet().get_cell("B5").set_value(88);
-        wbk.get_active_sheet().get_cell("B5").set_number_format(xlnt::number_format(xlnt::number_format::format::percentage_00));
+        wbk.get_active_sheet().get_cell("B5").set_number_format(xlnt::number_format::percentage_00());
         wbk.save(temp_file.GetFilename());
         
         if(PathHelper::FileExists(temp_file.GetFilename()))
diff --git a/tests/test_write_workbook.hpp b/tests/test_write_workbook.hpp
index a807d49d..bda0b867 100644
--- a/tests/test_write_workbook.hpp
+++ b/tests/test_write_workbook.hpp
@@ -68,7 +68,7 @@ public:
     {
         xlnt::workbook old_wb;
         auto saved_wb = xlnt::save_virtual_workbook(old_wb);
-        auto new_wb = xlnt::load_workbook(saved_wb);
+        auto new_wb = xlnt::excel_reader::load_workbook(saved_wb);
         TS_ASSERT(new_wb != nullptr);
     }