require("class")

Vector = class("Vector")

function Vector:_reset()
    self.sz = 0
    self.bus = {}
end

function Vector:ctor(t)
    self:_reset()
    if ((t ~= nil) and (type(t) == "table")) then
        for k, v in pairs(t) do
            local x = {}
            x.first = k
            x.second = v
            self:push_back(x)
        end --for
    end --if
end --func

function Vector:empty()
    return self.sz == 0
end

function Vector:push_back(val)
    self.bus[self.sz] = val
    self.sz = self.sz + 1
end

function Vector:pop_back()
    if (self:empty()) then
        return nil
    else
        local val = self.bus[self.sz - 1]
        self.bus[self.sz - 1] = nil
        self.sz = self.sz - 1
        return val
    end
end

function Vector:front()
    if (self:empty()) then
        return nil
    else
        return self.bus[0]
    end
end

function Vector:back()
    if (self:empty()) then
        return nil
    else
        return self.bus[self.sz - 1]
    end
end

function Vector:clear()
    self:_reset()
end

function Vector:at(index)
    if (type(index) ~= "number") then
        return nil
    elseif (self:empty()) then
        return nil
    elseif (index < 0) then
        return nil
    elseif (index >= self.sz) then
        return nil
    else
        return self.bus[index]
    end
end

function Vector:size()
    return self.sz
end

function Vector:insert_after(index, val)
    if (type(index) ~= "number") then
        return nil
    elseif (index >= self.sz) then
        return nil
    elseif (index < -1) then
        return nil
    else
        for i = self.sz - 1, index + 1, -1 do
            self.bus[i + 1] = self.bus[i]
        end
        self.bus[index + 1] = val
        self.sz = self.sz + 1
    end
end

function Vector:erase(index)
    if (type(index) ~= "number") then
        return nil
    elseif (index >= self.sz) then
        return nil
    elseif (index < 0) then
        return nil
    else
        for i = index + 1, self.sz - 1, 1 do
            self.bus[i - 1] = self.bus[i]
        end
        self.sz = self.sz - 1
    end
end