/**
 * Turn Markdown link shortcuts into XHTML <a> tags.
 */
showdown.subParser('anchors', function (text, options, globals) {
  'use strict';

  text = globals.converter._dispatch('anchors.before', text, options);

  var writeAnchorTag = function (wholeMatch, m1, m2, m3, m4, m5, m6, m7) {
    if (showdown.helper.isUndefined(m7)) {
      m7 = '';
    }
    wholeMatch = m1;
    var linkText = m2,
        linkId = m3.toLowerCase(),
        url = m4,
        title = m7;

    if (!url) {
      if (!linkId) {
        // lower-case and turn embedded newlines into spaces
        linkId = linkText.toLowerCase().replace(/ ?\n/g, ' ');
      }
      url = '#' + linkId;

      if (!showdown.helper.isUndefined(globals.gUrls[linkId])) {
        url = globals.gUrls[linkId];
        if (!showdown.helper.isUndefined(globals.gTitles[linkId])) {
          title = globals.gTitles[linkId];
        }
      } else {
        if (wholeMatch.search(/\(\s*\)$/m) > -1) {
          // Special case for explicit empty url
          url = '';
        } else {
          return wholeMatch;
        }
      }
    }

    url = showdown.helper.escapeCharacters(url, '*_', false);
    var result = '<a href="' + url + '"';

    if (title !== '' && title !== null) {
      title = title.replace(/"/g, '&quot;');
      title = showdown.helper.escapeCharacters(title, '*_', false);
      result += ' title="' + title + '"';
    }

    result += '>' + linkText + '</a>';

    return result;
  };

  // First, handle reference-style links: [link text] [id]
  /*
   text = text.replace(/
   (							// wrap whole match in $1
   \[
   (
   (?:
   \[[^\]]*\]		// allow brackets nested one level
   |
   [^\[]			// or anything else
   )*
   )
   \]

   [ ]?					// one optional space
   (?:\n[ ]*)?				// one optional newline followed by spaces

   \[
   (.*?)					// id = $3
   \]
   )()()()()					// pad remaining backreferences
   /g,_DoAnchors_callback);
   */
  text = text.replace(/(\[((?:\[[^\]]*]|[^\[\]])*)][ ]?(?:\n[ ]*)?\[(.*?)])()()()()/g, writeAnchorTag);

  //
  // Next, inline-style links: [link text](url "optional title")
  //

  /*
   text = text.replace(/
   (						// wrap whole match in $1
   \[
   (
   (?:
   \[[^\]]*\]	// allow brackets nested one level
   |
   [^\[\]]			// or anything else
   )
   )
   \]
   \(						// literal paren
   [ \t]*
   ()						// no id, so leave $3 empty
   <?(.*?)>?				// href = $4
   [ \t]*
   (						// $5
   (['"])				// quote char = $6
   (.*?)				// Title = $7
   \6					// matching quote
   [ \t]*				// ignore any spaces/tabs between closing quote and )
   )?						// title is optional
   \)
   )
   /g,writeAnchorTag);
   */
  text = text.replace(/(\[((?:\[[^\]]*]|[^\[\]])*)]\([ \t]*()<?(.*?(?:\(.*?\).*?)?)>?[ \t]*((['"])(.*?)\6[ \t]*)?\))/g,
                      writeAnchorTag);

  //
  // Last, handle reference-style shortcuts: [link text]
  // These must come last in case you've also got [link test][1]
  // or [link test](/foo)
  //

  /*
   text = text.replace(/
   (                // wrap whole match in $1
   \[
   ([^\[\]]+)       // link text = $2; can't contain '[' or ']'
   \]
   )()()()()()      // pad rest of backreferences
   /g, writeAnchorTag);
   */
  text = text.replace(/(\[([^\[\]]+)])()()()()()/g, writeAnchorTag);

  text = globals.converter._dispatch('anchors.after', text, options);
  return text;
});