var TurndownService = (function () {
    'use strict';
    
    function extend (destination) {
      for (var i = 1; i < arguments.length; i++) {
        var source = arguments[i];
        for (var key in source) {
          if (source.hasOwnProperty(key)) destination[key] = source[key];
        }
      }
      return destination
    }
    
    function repeat (character, count) {
      return Array(count + 1).join(character)
    }
    
    var blockElements = [
      'address', 'article', 'aside', 'audio', 'blockquote', 'body', 'canvas',
      'center', 'dd', 'dir', 'div', 'dl', 'dt', 'fieldset', 'figcaption',
      'figure', 'footer', 'form', 'frameset', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
      'header', 'hgroup', 'hr', 'html', 'isindex', 'li', 'main', 'menu', 'nav',
      'noframes', 'noscript', 'ol', 'output', 'p', 'pre', 'section', 'table',
      'tbody', 'td', 'tfoot', 'th', 'thead', 'tr', 'ul'
    ];
    
    function isBlock (node) {
      return blockElements.indexOf(node.nodeName.toLowerCase()) !== -1
    }
    
    var voidElements = [
      'area', 'base', 'br', 'col', 'command', 'embed', 'hr', 'img', 'input',
      'keygen', 'link', 'meta', 'param', 'source', 'track', 'wbr'
    ];
    
    function isVoid (node) {
      return voidElements.indexOf(node.nodeName.toLowerCase()) !== -1
    }
    
    var voidSelector = voidElements.join();
    function hasVoid (node) {
      return node.querySelector && node.querySelector(voidSelector)
    }
    
    var rules = {};
    
    rules.paragraph = {
      filter: 'p',
    
      replacement: function (content) {
        return '\n\n' + content + '\n\n'
      }
    };
    
    rules.lineBreak = {
      filter: 'br',
    
      replacement: function (content, node, options) {
        return options.br + '\n'
      }
    };
    
    rules.heading = {
      filter: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'],
    
      replacement: function (content, node, options) {
        var hLevel = Number(node.nodeName.charAt(1));
    
        if (options.headingStyle === 'setext' && hLevel < 3) {
          var underline = repeat((hLevel === 1 ? '=' : '-'), content.length);
          return (
            '\n\n' + content + '\n' + underline + '\n\n'
          )
        } else {
          return '\n\n' + repeat('#', hLevel) + ' ' + content + '\n\n'
        }
      }
    };
    
    rules.blockquote = {
      filter: 'blockquote',
    
      replacement: function (content) {
        content = content.replace(/^\n+|\n+$/g, '');
        content = content.replace(/^/gm, '> ');
        return '\n\n' + content + '\n\n'
      }
    };
    
    rules.list = {
      filter: ['ul', 'ol'],
    
      replacement: function (content, node) {
        var parent = node.parentNode;
        if (parent.nodeName === 'LI' && parent.lastElementChild === node) {
          return '\n' + content
        } else {
          return '\n\n' + content + '\n\n'
        }
      }
    };
    
    rules.listItem = {
      filter: 'li',
    
      replacement: function (content, node, options) {
        content = content
          .replace(/^\n+/, '') // remove leading newlines
          .replace(/\n+$/, '\n') // replace trailing newlines with just a single one
          .replace(/\n/gm, '\n    '); // indent
        var prefix = options.bulletListMarker + '   ';
        var parent = node.parentNode;
        if (parent.nodeName === 'OL') {
          var start = parent.getAttribute('start');
          var index = Array.prototype.indexOf.call(parent.children, node);
          prefix = (start ? Number(start) + index : index + 1) + '.  ';
        }
        return (
          prefix + content + (node.nextSibling && !/\n$/.test(content) ? '\n' : '')
        )
      }
    };
    
    rules.indentedCodeBlock = {
      filter: function (node, options) {
        return (
          options.codeBlockStyle === 'indented' &&
          node.nodeName === 'PRE' &&
          node.firstChild &&
          node.firstChild.nodeName === 'CODE'
        )
      },
    
      replacement: function (content, node, options) {
        return (
          '\n\n    ' +
          node.firstChild.textContent.replace(/\n/g, '\n    ') +
          '\n\n'
        )
      }
    };
    
    rules.fencedCodeBlock = {
      filter: function (node, options) {
        return (
          options.codeBlockStyle === 'fenced' &&
          node.nodeName === 'PRE' &&
          node.firstChild &&
          node.firstChild.nodeName === 'CODE'
        )
      },
    
      replacement: function (content, node, options) {
        var className = node.firstChild.className || '';
        var language = (className.match(/language-(\S+)/) || [null, ''])[1];
    
        return (
          '\n\n' + options.fence + language + '\n' +
          node.firstChild.textContent +
          '\n' + options.fence + '\n\n'
        )
      }
    };
    
    rules.horizontalRule = {
      filter: 'hr',
    
      replacement: function (content, node, options) {
        return '\n\n' + options.hr + '\n\n'
      }
    };
    
    rules.inlineLink = {
      filter: function (node, options) {
        return (
          options.linkStyle === 'inlined' &&
          node.nodeName === 'A' &&
          node.getAttribute('href')
        )
      },
    
      replacement: function (content, node) {
        var href = node.getAttribute('href');
        var title = node.title ? ' "' + node.title + '"' : '';
        return '[' + content + '](' + href + title + ')'
      }
    };
    
    rules.referenceLink = {
      filter: function (node, options) {
        return (
          options.linkStyle === 'referenced' &&
          node.nodeName === 'A' &&
          node.getAttribute('href')
        )
      },
    
      replacement: function (content, node, options) {
        var href = node.getAttribute('href');
        var title = node.title ? ' "' + node.title + '"' : '';
        var replacement;
        var reference;
    
        switch (options.linkReferenceStyle) {
          case 'collapsed':
            replacement = '[' + content + '][]';
            reference = '[' + content + ']: ' + href + title;
            break
          case 'shortcut':
            replacement = '[' + content + ']';
            reference = '[' + content + ']: ' + href + title;
            break
          default:
            var id = this.references.length + 1;
            replacement = '[' + content + '][' + id + ']';
            reference = '[' + id + ']: ' + href + title;
        }
    
        this.references.push(reference);
        return replacement
      },
    
      references: [],
    
      append: function (options) {
        var references = '';
        if (this.references.length) {
          references = '\n\n' + this.references.join('\n') + '\n\n';
          this.references = []; // Reset references
        }
        return references
      }
    };
    
    rules.emphasis = {
      filter: ['em', 'i'],
    
      replacement: function (content, node, options) {
        if (!content.trim()) return ''
        return options.emDelimiter + content + options.emDelimiter
      }
    };
    
    rules.strong = {
      filter: ['strong', 'b'],
    
      replacement: function (content, node, options) {
        if (!content.trim()) return ''
        return options.strongDelimiter + content + options.strongDelimiter
      }
    };
    
    rules.code = {
      filter: function (node) {
        var hasSiblings = node.previousSibling || node.nextSibling;
        var isCodeBlock = node.parentNode.nodeName === 'PRE' && !hasSiblings;
    
        return node.nodeName === 'CODE' && !isCodeBlock
      },
    
      replacement: function (content) {
        if (!content.trim()) return ''
    
        var delimiter = '`';
        var leadingSpace = '';
        var trailingSpace = '';
        var matches = content.match(/`+/gm);
        if (matches) {
          if (/^`/.test(content)) leadingSpace = ' ';
          if (/`$/.test(content)) trailingSpace = ' ';
          while (matches.indexOf(delimiter) !== -1) delimiter = delimiter + '`';
        }
    
        return delimiter + leadingSpace + content + trailingSpace + delimiter
      }
    };
    
    rules.image = {
      filter: 'img',
    
      replacement: function (content, node) {
        var alt = node.alt || '';
        var src = node.getAttribute('src') || '';
        var title = node.title || '';
        var titlePart = title ? ' "' + title + '"' : '';
        return src ? '![' + alt + ']' + '(' + src + titlePart + ')' : ''
      }
    };
    
    /**
     * Manages a collection of rules used to convert HTML to Markdown
     */
    
    function Rules (options) {
      this.options = options;
      this._keep = [];
      this._remove = [];
    
      this.blankRule = {
        replacement: options.blankReplacement
      };
    
      this.keepReplacement = options.keepReplacement;
    
      this.defaultRule = {
        replacement: options.defaultReplacement
      };
    
      this.array = [];
      for (var key in options.rules) this.array.push(options.rules[key]);
    }
    
    Rules.prototype = {
      add: function (key, rule) {
        this.array.unshift(rule);
      },
    
      keep: function (filter) {
        this._keep.unshift({
          filter: filter,
          replacement: this.keepReplacement
        });
      },
    
      remove: function (filter) {
        this._remove.unshift({
          filter: filter,
          replacement: function () {
            return ''
          }
        });
      },
    
      forNode: function (node) {
        if (node.isBlank) return this.blankRule
        var rule;
    
        if ((rule = findRule(this.array, node, this.options))) return rule
        if ((rule = findRule(this._keep, node, this.options))) return rule
        if ((rule = findRule(this._remove, node, this.options))) return rule
    
        return this.defaultRule
      },
    
      forEach: function (fn) {
        for (var i = 0; i < this.array.length; i++) fn(this.array[i], i);
      }
    };
    
    function findRule (rules, node, options) {
      for (var i = 0; i < rules.length; i++) {
        var rule = rules[i];
        if (filterValue(rule, node, options)) return rule
      }
      return void 0
    }
    
    function filterValue (rule, node, options) {
      var filter = rule.filter;
      if (typeof filter === 'string') {
        if (filter === node.nodeName.toLowerCase()) return true
      } else if (Array.isArray(filter)) {
        if (filter.indexOf(node.nodeName.toLowerCase()) > -1) return true
      } else if (typeof filter === 'function') {
        if (filter.call(rule, node, options)) return true
      } else {
        throw new TypeError('`filter` needs to be a string, array, or function')
      }
    }
    
    /**
     * The collapseWhitespace function is adapted from collapse-whitespace
     * by Luc Thevenard.
     *
     * The MIT License (MIT)
     *
     * Copyright (c) 2014 Luc Thevenard <lucthevenard@gmail.com>
     *
     * 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, ARISING FROM,
     * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     * THE SOFTWARE.
     */
    
    /**
     * collapseWhitespace(options) removes extraneous whitespace from an the given element.
     *
     * @param {Object} options
     */
    function collapseWhitespace (options) {
      var element = options.element;
      var isBlock = options.isBlock;
      var isVoid = options.isVoid;
      var isPre = options.isPre || function (node) {
        return node.nodeName === 'PRE'
      };
    
      if (!element.firstChild || isPre(element)) return
    
      var prevText = null;
      var prevVoid = false;
    
      var prev = null;
      var node = next(prev, element, isPre);
    
      while (node !== element) {
        if (node.nodeType === 3 || node.nodeType === 4) { // Node.TEXT_NODE or Node.CDATA_SECTION_NODE
          var text = node.data.replace(/[ \r\n\t]+/g, ' ');
    
          if ((!prevText || / $/.test(prevText.data)) &&
              !prevVoid && text[0] === ' ') {
            text = text.substr(1);
          }
    
          // `text` might be empty at this point.
          if (!text) {
            node = remove(node);
            continue
          }
    
          node.data = text;
    
          prevText = node;
        } else if (node.nodeType === 1) { // Node.ELEMENT_NODE
          if (isBlock(node) || node.nodeName === 'BR') {
            if (prevText) {
              prevText.data = prevText.data.replace(/ $/, '');
            }
    
            prevText = null;
            prevVoid = false;
          } else if (isVoid(node)) {
            // Avoid trimming space around non-block, non-BR void elements.
            prevText = null;
            prevVoid = true;
          }
        } else {
          node = remove(node);
          continue
        }
    
        var nextNode = next(prev, node, isPre);
        prev = node;
        node = nextNode;
      }
    
      if (prevText) {
        prevText.data = prevText.data.replace(/ $/, '');
        if (!prevText.data) {
          remove(prevText);
        }
      }
    }
    
    /**
     * remove(node) removes the given node from the DOM and returns the
     * next node in the sequence.
     *
     * @param {Node} node
     * @return {Node} node
     */
    function remove (node) {
      var next = node.nextSibling || node.parentNode;
    
      node.parentNode.removeChild(node);
    
      return next
    }
    
    /**
     * next(prev, current, isPre) returns the next node in the sequence, given the
     * current and previous nodes.
     *
     * @param {Node} prev
     * @param {Node} current
     * @param {Function} isPre
     * @return {Node}
     */
    function next (prev, current, isPre) {
      if ((prev && prev.parentNode === current) || isPre(current)) {
        return current.nextSibling || current.parentNode
      }
    
      return current.firstChild || current.nextSibling || current.parentNode
    }
    
    /*
     * Set up window for Node.js
     */
    
    var root = (typeof window !== 'undefined' ? window : {});
    
    /*
     * Parsing HTML strings
     */
    
    function canParseHTMLNatively () {
      var Parser = root.DOMParser;
      var canParse = false;
    
      // Adapted from https://gist.github.com/1129031
      // Firefox/Opera/IE throw errors on unsupported types
      try {
        // WebKit returns null on unsupported types
        if (new Parser().parseFromString('', 'text/html')) {
          canParse = true;
        }
      } catch (e) {}
    
      return canParse
    }
    
    function createHTMLParser () {
      var Parser = function () {};
    
      {
        if (shouldUseActiveX()) {
          Parser.prototype.parseFromString = function (string) {
            var doc = new window.ActiveXObject('htmlfile');
            doc.designMode = 'on'; // disable on-page scripts
            doc.open();
            doc.write(string);
            doc.close();
            return doc
          };
        } else {
          Parser.prototype.parseFromString = function (string) {
            var doc = document.implementation.createHTMLDocument('');
            doc.open();
            doc.write(string);
            doc.close();
            return doc
          };
        }
      }
      return Parser
    }
    
    function shouldUseActiveX () {
      var useActiveX = false;
      try {
        document.implementation.createHTMLDocument('').open();
      } catch (e) {
        if (window.ActiveXObject) useActiveX = true;
      }
      return useActiveX
    }
    
    var HTMLParser = canParseHTMLNatively() ? root.DOMParser : createHTMLParser();
    
    function RootNode (input) {
      var root;
      if (typeof input === 'string') {
        var doc = htmlParser().parseFromString(
          // DOM parsers arrange elements in the <head> and <body>.
          // Wrapping in a custom element ensures elements are reliably arranged in
          // a single element.
          '<x-turndown id="turndown-root">' + input + '</x-turndown>',
          'text/html'
        );
        root = doc.getElementById('turndown-root');
      } else {
        root = input.cloneNode(true);
      }
      collapseWhitespace({
        element: root,
        isBlock: isBlock,
        isVoid: isVoid
      });
    
      return root
    }
    
    var _htmlParser;
    function htmlParser () {
      _htmlParser = _htmlParser || new HTMLParser();
      return _htmlParser
    }
    
    function Node (node) {
      node.isBlock = isBlock(node);
      node.isCode = node.nodeName.toLowerCase() === 'code' || node.parentNode.isCode;
      node.isBlank = isBlank(node);
      node.flankingWhitespace = flankingWhitespace(node);
      return node
    }
    
    function isBlank (node) {
      return (
        ['A', 'TH', 'TD', 'IFRAME', 'SCRIPT', 'AUDIO', 'VIDEO'].indexOf(node.nodeName) === -1 &&
        /^\s*$/i.test(node.textContent) &&
        !isVoid(node) &&
        !hasVoid(node)
      )
    }
    
    function flankingWhitespace (node) {
      var leading = '';
      var trailing = '';
    
      if (!node.isBlock) {
        var hasLeading = /^[ \r\n\t]/.test(node.textContent);
        var hasTrailing = /[ \r\n\t]$/.test(node.textContent);
    
        if (hasLeading && !isFlankedByWhitespace('left', node)) {
          leading = ' ';
        }
        if (hasTrailing && !isFlankedByWhitespace('right', node)) {
          trailing = ' ';
        }
      }
    
      return { leading: leading, trailing: trailing }
    }
    
    function isFlankedByWhitespace (side, node) {
      var sibling;
      var regExp;
      var isFlanked;
    
      if (side === 'left') {
        sibling = node.previousSibling;
        regExp = / $/;
      } else {
        sibling = node.nextSibling;
        regExp = /^ /;
      }
    
      if (sibling) {
        if (sibling.nodeType === 3) {
          isFlanked = regExp.test(sibling.nodeValue);
        } else if (sibling.nodeType === 1 && !isBlock(sibling)) {
          isFlanked = regExp.test(sibling.textContent);
        }
      }
      return isFlanked
    }
    
    var reduce = Array.prototype.reduce;
    var leadingNewLinesRegExp = /^\n*/;
    var trailingNewLinesRegExp = /\n*$/;
    var escapes = [
      [/\\/g, '\\\\'],
      [/\*/g, '\\*'],
      [/^-/g, '\\-'],
      [/^\+ /g, '\\+ '],
      [/^(=+)/g, '\\$1'],
      [/^(#{1,6}) /g, '\\$1 '],
      [/`/g, '\\`'],
      [/^~~~/g, '\\~~~'],
      [/\[/g, '\\['],
      [/\]/g, '\\]'],
      [/^>/g, '\\>'],
      [/_/g, '\\_'],
      [/^(\d+)\. /g, '$1\\. ']
    ];
    
    function TurndownService (options) {
      if (!(this instanceof TurndownService)) return new TurndownService(options)
    
      var defaults = {
        rules: rules,
        headingStyle: 'setext',
        hr: '* * *',
        bulletListMarker: '*',
        codeBlockStyle: 'indented',
        fence: '```',
        emDelimiter: '_',
        strongDelimiter: '**',
        linkStyle: 'inlined',
        linkReferenceStyle: 'full',
        br: '  ',
        blankReplacement: function (content, node) {
          return node.isBlock ? '\n\n' : ''
        },
        keepReplacement: function (content, node) {
          return node.isBlock ? '\n\n' + node.outerHTML + '\n\n' : node.outerHTML
        },
        defaultReplacement: function (content, node) {
          return node.isBlock ? '\n\n' + content + '\n\n' : content
        }
      };
      this.options = extend({}, defaults, options);
      this.rules = new Rules(this.options);
    }
    
    TurndownService.prototype = {
      /**
       * The entry point for converting a string or DOM node to Markdown
       * @public
       * @param {String|HTMLElement} input The string or DOM node to convert
       * @returns A Markdown representation of the input
       * @type String
       */
    
      turndown: function (input) {
        if (!canConvert(input)) {
          throw new TypeError(
            input + ' is not a string, or an element/document/fragment node.'
          )
        }
    
        if (input === '') return ''
    
        var output = process.call(this, new RootNode(input));
        return postProcess.call(this, output)
      },
    
      /**
       * Add one or more plugins
       * @public
       * @param {Function|Array} plugin The plugin or array of plugins to add
       * @returns The Turndown instance for chaining
       * @type Object
       */
    
      use: function (plugin) {
        if (Array.isArray(plugin)) {
          for (var i = 0; i < plugin.length; i++) this.use(plugin[i]);
        } else if (typeof plugin === 'function') {
          plugin(this);
        } else {
          throw new TypeError('plugin must be a Function or an Array of Functions')
        }
        return this
      },
    
      /**
       * Adds a rule
       * @public
       * @param {String} key The unique key of the rule
       * @param {Object} rule The rule
       * @returns The Turndown instance for chaining
       * @type Object
       */
    
      addRule: function (key, rule) {
        this.rules.add(key, rule);
        return this
      },
    
      /**
       * Keep a node (as HTML) that matches the filter
       * @public
       * @param {String|Array|Function} filter The unique key of the rule
       * @returns The Turndown instance for chaining
       * @type Object
       */
    
      keep: function (filter) {
        this.rules.keep(filter);
        return this
      },
    
      /**
       * Remove a node that matches the filter
       * @public
       * @param {String|Array|Function} filter The unique key of the rule
       * @returns The Turndown instance for chaining
       * @type Object
       */
    
      remove: function (filter) {
        this.rules.remove(filter);
        return this
      },
    
      /**
       * Escapes Markdown syntax
       * @public
       * @param {String} string The string to escape
       * @returns A string with Markdown syntax escaped
       * @type String
       */
    
      escape: function (string) {
        return escapes.reduce(function (accumulator, escape) {
          return accumulator.replace(escape[0], escape[1])
        }, string)
      }
    };
    
    /**
     * Reduces a DOM node down to its Markdown string equivalent
     * @private
     * @param {HTMLElement} parentNode The node to convert
     * @returns A Markdown representation of the node
     * @type String
     */
    
    function process (parentNode) {
      var self = this;
      return reduce.call(parentNode.childNodes, function (output, node) {
        node = new Node(node);
    
        var replacement = '';
        if (node.nodeType === 3) {
          replacement = node.isCode ? node.nodeValue : self.escape(node.nodeValue);
        } else if (node.nodeType === 1) {
          replacement = replacementForNode.call(self, node);
        }
    
        return join(output, replacement)
      }, '')
    }
    
    /**
     * Appends strings as each rule requires and trims the output
     * @private
     * @param {String} output The conversion output
     * @returns A trimmed version of the ouput
     * @type String
     */
    
    function postProcess (output) {
      var self = this;
      this.rules.forEach(function (rule) {
        if (typeof rule.append === 'function') {
          output = join(output, rule.append(self.options));
        }
      });
    
      return output.replace(/^[\t\r\n]+/, '').replace(/[\t\r\n\s]+$/, '')
    }
    
    /**
     * Converts an element node to its Markdown equivalent
     * @private
     * @param {HTMLElement} node The node to convert
     * @returns A Markdown representation of the node
     * @type String
     */
    
    function replacementForNode (node) {
      var rule = this.rules.forNode(node);
      var content = process.call(this, node);
      var whitespace = node.flankingWhitespace;
      if (whitespace.leading || whitespace.trailing) content = content.trim();
      return (
        whitespace.leading +
        rule.replacement(content, node, this.options) +
        whitespace.trailing
      )
    }
    
    /**
     * Determines the new lines between the current output and the replacement
     * @private
     * @param {String} output The current conversion output
     * @param {String} replacement The string to append to the output
     * @returns The whitespace to separate the current output and the replacement
     * @type String
     */
    
    function separatingNewlines (output, replacement) {
      var newlines = [
        output.match(trailingNewLinesRegExp)[0],
        replacement.match(leadingNewLinesRegExp)[0]
      ].sort();
      var maxNewlines = newlines[newlines.length - 1];
      return maxNewlines.length < 2 ? maxNewlines : '\n\n'
    }
    
    function join (string1, string2) {
      var separator = separatingNewlines(string1, string2);
    
      // Remove trailing/leading newlines and replace with separator
      string1 = string1.replace(trailingNewLinesRegExp, '');
      string2 = string2.replace(leadingNewLinesRegExp, '');
    
      return string1 + separator + string2
    }
    
    /**
     * Determines whether an input can be converted
     * @private
     * @param {String|HTMLElement} input Describe this parameter
     * @returns Describe what it returns
     * @type String|Object|Array|Boolean|Number
     */
    
    function canConvert (input) {
      return (
        input != null && (
          typeof input === 'string' ||
          (input.nodeType && (
            input.nodeType === 1 || input.nodeType === 9 || input.nodeType === 11
          ))
        )
      )
    }
    
    return TurndownService;
    
    }());
    