source: trunk/HeuristicLab.ExtLibs/HeuristicLab.EPPlus/4.0.3/EPPlus-4.0.3/Style/ExcelRichTextHtmlUtility.cs

/*******************************************************************************
 * You may amend and distribute as you like, but don't remove this header!
 *
 * EPPlus provides server-side generation of Excel 2007/2010 spreadsheets.
 * See http://www.codeplex.com/EPPlus for details.
 *
 * Copyright (C) 2011  Jan Källman
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.

 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU Lesser General Public License for more details.
 *
 * The GNU Lesser General Public License can be viewed at http://www.opensource.org/licenses/lgpl-license.php
 * If you unfamiliar with this license or have questions about it, here is an http://www.gnu.org/licenses/gpl-faq.html
 *
 * All code and executables are provided "as is" with no warranty either express or implied. 
 * The author accepts no liability for any damage or loss of business that this product may cause.
 *
 * Code change notes:
 * 
 * Author       Change            Date
 * ******************************************************************************
 * Richard Tallent    Initial Release       2012-08-13
 *******************************************************************************/
using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace OfficeOpenXml.Style
{
  public class ExcelRichTextHtmlUtility
  {

    /// <summary>
    /// Provides basic HTML support by converting well-behaved HTML into appropriate RichText blocks.
    /// HTML support is limited, and does not include font colors, sizes, or typefaces at this time,
    /// and also does not support CSS style attributes. It does support line breaks using the BR tag.
    ///
    /// This routine parses the HTML into RegEx pairings of an HTML tag and the text until the NEXT 
    /// tag (if any). The tag is parsed to determine the setting change to be applied to the last set
    /// of settings, and if the text is not blank, a new block is added to rich text.
    /// </summary>
    /// <param name="range"></param>
    /// <param name="html">The HTML to parse into RichText</param>
    /// <param name="defaultFontName"></param>
    /// <param name="defaultFontSize"></param>

    public static void SetRichTextFromHtml(ExcelRange range, string html, string defaultFontName, short defaultFontSize)
    {
      // Reset the cell value, just in case there is an existing RichText value.
      range.Value = "";

      // Sanity check for blank values, skips creating Regex objects for performance.
      if (String.IsNullOrEmpty(html))
      {
        range.IsRichText = false;
        return;
      }

      // Change all BR tags to line breaks. http://epplus.codeplex.com/discussions/238692/
      // Cells with line breaks aren't necessarily considered rich text, so this is performed
      // before parsing the HTML tags.
      html = System.Text.RegularExpressions.Regex.Replace(html, @"<br[^>]*>", "\r\n", RegexOptions.Compiled | RegexOptions.IgnoreCase);

      string tag;
      string text;
      ExcelRichText thisrt = null;
      bool isFirst = true;

      // Get all pairs of legitimate tags and the text between them. This loop will
      // only execute if there is at least one start or end tag.
      foreach (Match m in System.Text.RegularExpressions.Regex.Matches(html, @"<(/?[a-z]+)[^<>]*>([\s\S]*?)(?=</?[a-z]+[^<>]*>|$)", RegexOptions.Compiled | RegexOptions.IgnoreCase))
      {
        if (isFirst)
        {
          // On the very first match, set up the initial rich text object with
          // the defaults for the text BEFORE the match.
          range.IsRichText = true;
          thisrt = range.RichText.Add(CleanText(html.Substring(0, m.Index))); // May be 0-length
          thisrt.Size = defaultFontSize;                    // Set the default font size
          thisrt.FontName = defaultFontName;                  // Set the default font name
          isFirst = false;
        }
        // Get the tag and the block of text until the NEXT tag or EOS. If there are HTML entities
        // encoded, unencode them, they should be passed to RichText as normal characters (other
        // than non-breaking spaces, which should be replaced with normal spaces, they break Excel.
        tag = m.Groups[1].Captures[0].Value;
        text = CleanText(m.Groups[2].Captures[0].Value);

        if (thisrt.Text == "")
        {
          // The most recent rich text block wasn't *actually* used last time around, so update
          // the text and keep it as the "current" block. This happens with the first block if
          // it starts with a tag, and may happen later if tags come one right after the other.
          thisrt.Text = text;
        }
        else
        {
          // The current rich text block has some text, so create a new one. RichText.Add()
          // automatically applies the settings from the previous block, other than vertical
          // alignment.
          thisrt = range.RichText.Add(text);
        }
        // Override the settings based on the current tag, keep all other settings.
        SetStyleFromTag(tag, thisrt);
      }

      if (thisrt == null)
      {
        // No HTML tags were found, so treat this as a normal text value.
        range.IsRichText = false;
        range.Value = CleanText(html);
      }
      else if (String.IsNullOrEmpty(thisrt.Text))
      {
        // Rich text was found, but the last node contains no text, so remove it. This can happen if,
        // say, the end of the string is an end tag or unsupported tag (common).
        range.RichText.Remove(thisrt);

        // Failsafe -- the HTML may be just tags, no text, in which case there may be no rich text
        // directives that remain. If that is the case, turn off rich text and treat this like a blank
        // cell value.
        if (range.RichText.Count == 0)
        {
          range.IsRichText = false;
          range.Value = "";
        }

      }

    }

    private static void SetStyleFromTag(string tag, ExcelRichText settings)
    {
      switch (tag.ToLower())
      {
        case "b":
        case "strong":
          settings.Bold = true;
          break;
        case "i":
        case "em":
          settings.Italic = true;
          break;
        case "u":
          settings.UnderLine = true;
          break;
        case "s":
        case "strike":
          settings.Strike = true;
          break;
        case "sup":
          settings.VerticalAlign = ExcelVerticalAlignmentFont.Superscript;
          break;
        case "sub":
          settings.VerticalAlign = ExcelVerticalAlignmentFont.Subscript;
          break;
        case "/b":
        case "/strong":
          settings.Bold = false;
          break;
        case "/i":
        case "/em":
          settings.Italic = false;
          break;
        case "/u":
          settings.UnderLine = false;
          break;
        case "/s":
        case "/strike":
          settings.Strike = false;
          break;
        case "/sup":
        case "/sub":
          settings.VerticalAlign = ExcelVerticalAlignmentFont.None;
          break;
        default:
          // unsupported HTML, no style change
          break;
      }
    }

    private static string CleanText(string s)
    {
      // Need to convert HTML entities (named or numbered) into actual Unicode characters
      s = System.Web.HttpUtility.HtmlDecode(s);
      // Remove any non-breaking spaces, kills Excel
      s = s.Replace("\u00A0", " ");
      return s;
    }

  }
}