259 lines
10 KiB
C#
259 lines
10 KiB
C#
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// "Therefore those skilled at the unorthodox
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// are infinite as heaven and earth,
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// inexhaustible as the great rivers.
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// When they come to an end,
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// they begin again,
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// like the days and months;
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// they die and are reborn,
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// like the four seasons."
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//
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// - Sun Tsu,
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// "The Art of War"
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using System;
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using System.Collections.Generic;
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using TheArtOfDev.HtmlRenderer.Core.Dom;
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using TheArtOfDev.HtmlRenderer.Core.Utils;
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namespace TheArtOfDev.HtmlRenderer.Core.Parse
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{
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/// <summary>
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///
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/// </summary>
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internal static class HtmlParser
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{
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/// <summary>
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/// Parses the source html to css boxes tree structure.
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/// </summary>
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/// <param name="source">the html source to parse</param>
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public static CssBox ParseDocument(string source)
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{
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var root = CssBox.CreateBlock();
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var curBox = root;
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int endIdx = 0;
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int startIdx = 0;
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while (startIdx >= 0)
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{
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var tagIdx = source.IndexOf('<', startIdx);
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if (tagIdx >= 0 && tagIdx < source.Length)
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{
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// add the html text as anon css box to the structure
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AddTextBox(source, startIdx, tagIdx, ref curBox);
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if (source[tagIdx + 1] == '!')
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{
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if (source[tagIdx + 2] == '-')
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{
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// skip the html comment elements (<!-- bla -->)
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startIdx = source.IndexOf("-->", tagIdx + 2);
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endIdx = startIdx > 0 ? startIdx + 3 : tagIdx + 2;
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}
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else
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{
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// skip the html crap elements (<!crap bla>)
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startIdx = source.IndexOf(">", tagIdx + 2);
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endIdx = startIdx > 0 ? startIdx + 1 : tagIdx + 2;
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}
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}
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else
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{
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// parse element tag to css box structure
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endIdx = ParseHtmlTag(source, tagIdx, ref curBox) + 1;
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if (curBox.HtmlTag != null && curBox.HtmlTag.Name.Equals(HtmlConstants.Style, StringComparison.OrdinalIgnoreCase))
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{
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var endIdxS = endIdx;
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endIdx = source.IndexOf("</style>", endIdx, StringComparison.OrdinalIgnoreCase);
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if (endIdx > -1)
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AddTextBox(source, endIdxS, endIdx, ref curBox);
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}
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}
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}
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startIdx = tagIdx > -1 && endIdx > 0 ? endIdx : -1;
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}
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// handle pieces of html without proper structure
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if (endIdx > -1 && endIdx < source.Length)
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{
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// there is text after the end of last element
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var endText = new SubString(source, endIdx, source.Length - endIdx);
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if (!endText.IsEmptyOrWhitespace())
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{
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var abox = CssBox.CreateBox(root);
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abox.Text = endText;
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}
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}
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return root;
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}
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#region Private methods
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/// <summary>
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/// Add html text anon box to the current box, this box will have the rendered text<br/>
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/// Adding box also for text that contains only whitespaces because we don't know yet if
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/// the box is preformatted. At later stage they will be removed if not relevant.
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/// </summary>
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/// <param name="source">the html source to parse</param>
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/// <param name="startIdx">the start of the html part</param>
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/// <param name="tagIdx">the index of the next html tag</param>
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/// <param name="curBox">the current box in html tree parsing</param>
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private static void AddTextBox(string source, int startIdx, int tagIdx, ref CssBox curBox)
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{
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var text = tagIdx > startIdx ? new SubString(source, startIdx, tagIdx - startIdx) : null;
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if (text != null)
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{
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var abox = CssBox.CreateBox(curBox);
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abox.Text = text;
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}
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}
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/// <summary>
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/// Parse the html part, the part from prev parsing index to the beginning of the next html tag.<br/>
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/// </summary>
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/// <param name="source">the html source to parse</param>
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/// <param name="tagIdx">the index of the next html tag</param>
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/// <param name="curBox">the current box in html tree parsing</param>
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/// <returns>the end of the parsed part, the new start index</returns>
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private static int ParseHtmlTag(string source, int tagIdx, ref CssBox curBox)
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{
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var endIdx = source.IndexOf('>', tagIdx + 1);
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if (endIdx > 0)
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{
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string tagName;
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Dictionary<string, string> tagAttributes;
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var length = endIdx - tagIdx + 1 - (source[endIdx - 1] == '/' ? 1 : 0);
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if (ParseHtmlTag(source, tagIdx, length, out tagName, out tagAttributes))
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{
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if (!HtmlUtils.IsSingleTag(tagName) && curBox.ParentBox != null)
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{
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// need to find the parent tag to go one level up
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curBox = DomUtils.FindParent(curBox.ParentBox, tagName, curBox);
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}
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}
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else if (!string.IsNullOrEmpty(tagName))
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{
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//new SubString(source, lastEnd + 1, tagmatch.Index - lastEnd - 1)
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var isSingle = HtmlUtils.IsSingleTag(tagName) || source[endIdx - 1] == '/';
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var tag = new HtmlTag(tagName, isSingle, tagAttributes);
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if (isSingle)
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{
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// the current box is not changed
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CssBox.CreateBox(tag, curBox);
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}
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else
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{
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// go one level down, make the new box the current box
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curBox = CssBox.CreateBox(tag, curBox);
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}
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}
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else
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{
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endIdx = tagIdx + 1;
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}
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}
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return endIdx;
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}
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/// <summary>
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/// Parse raw html tag source to <seealso cref="HtmlTag"/> object.<br/>
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/// Extract attributes found on the tag.
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/// </summary>
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/// <param name="source">the html source to parse</param>
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/// <param name="idx">the start index of the tag in the source</param>
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/// <param name="length">the length of the tag from the start index in the source</param>
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/// <param name="name">return the name of the html tag</param>
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/// <param name="attributes">return the dictionary of tag attributes</param>
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/// <returns>true - the tag is closing tag, false - otherwise</returns>
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private static bool ParseHtmlTag(string source, int idx, int length, out string name, out Dictionary<string, string> attributes)
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{
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idx++;
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length = length - (source[idx + length - 3] == '/' ? 3 : 2);
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// Check if is end tag
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var isClosing = false;
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if (source[idx] == '/')
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{
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idx++;
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length--;
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isClosing = true;
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}
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int spaceIdx = idx;
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while (spaceIdx < idx + length && !char.IsWhiteSpace(source, spaceIdx))
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spaceIdx++;
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// Get the name of the tag
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name = source.Substring(idx, spaceIdx - idx).ToLower();
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attributes = null;
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if (!isClosing && idx + length > spaceIdx)
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{
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ExtractAttributes(source, spaceIdx, length - (spaceIdx - idx), out attributes);
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}
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return isClosing;
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}
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/// <summary>
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/// Extract html tag attributes from the given sub-string.
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/// </summary>
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/// <param name="source">the html source to parse</param>
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/// <param name="idx">the start index of the tag attributes in the source</param>
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/// <param name="length">the length of the tag attributes from the start index in the source</param>
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/// <param name="attributes">return the dictionary of tag attributes</param>
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private static void ExtractAttributes(string source, int idx, int length, out Dictionary<string, string> attributes)
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{
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attributes = null;
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int startIdx = idx;
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while (startIdx < idx + length)
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{
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while (startIdx < idx + length && char.IsWhiteSpace(source, startIdx))
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startIdx++;
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var endIdx = startIdx + 1;
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while (endIdx < idx + length && !char.IsWhiteSpace(source, endIdx) && source[endIdx] != '=')
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endIdx++;
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if (startIdx < idx + length)
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{
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var key = source.Substring(startIdx, endIdx - startIdx);
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startIdx = endIdx + 1;
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while (startIdx < idx + length && (char.IsWhiteSpace(source, startIdx) || source[startIdx] == '='))
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startIdx++;
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bool hasPChar = false;
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char pChar = source[startIdx];
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if (pChar == '"' || pChar == '\'')
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{
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hasPChar = true;
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startIdx++;
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}
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endIdx = startIdx + (hasPChar ? 0 : 1);
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while (endIdx < idx + length && (hasPChar ? source[endIdx] != pChar : !char.IsWhiteSpace(source, endIdx)))
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endIdx++;
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var value = source.Substring(startIdx, endIdx - startIdx);
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value = HtmlUtils.DecodeHtml(value);
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if (!string.IsNullOrEmpty(key) && !string.IsNullOrEmpty(value))
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{
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if (attributes == null)
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attributes = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase);
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attributes[key.ToLower()] = value;
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}
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startIdx = endIdx + (hasPChar ? 2 : 1);
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}
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}
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}
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#endregion
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}
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}
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