/*
 * NReadability
 * http://code.google.com/p/nreadability/
 * 
 * Copyright 2010 Marek Stój
 * http://immortal.pl/
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Text;
using System.Text.RegularExpressions;
using System.Xml;
using System.Xml.Linq;
using PocketSharp.Ports.Sgml;
using System.IO;

namespace PocketSharp.Ports.NReadability
{
  /// <summary>
  /// A class for constructing a DOM from HTML markup.
  /// </summary>
  public class SgmlDomBuilder
  {
    #region Public methods

    /// <summary>
    /// Constructs a DOM (System.Xml.Linq.XDocument) from HTML markup.
    /// </summary>
    /// <param name="htmlContent">HTML markup from which the DOM is to be constructed.</param>
    /// <returns>System.Linq.Xml.XDocument instance which is a DOM of the provided HTML markup.</returns>
    public XDocument BuildDocument(string htmlContent)
    {
      if (htmlContent == null)
      {
        throw new ArgumentNullException("htmlContent");
      }

      if (htmlContent.Trim().Length == 0)
      {
        return new XDocument();
      }

      // "trim end" htmlContent to ...</html>$ (codinghorror.com puts some scripts after the </html> - sic!)
      const string htmlEnd = "</html";
      int indexOfHtmlEnd = htmlContent.LastIndexOf(htmlEnd);

      if (indexOfHtmlEnd != -1)
      {
        int indexOfHtmlEndBracket = htmlContent.IndexOf('>', indexOfHtmlEnd);

        if (indexOfHtmlEndBracket != -1)
        {
          htmlContent = htmlContent.Substring(0, indexOfHtmlEndBracket + 1);
        }
      }

      XDocument document;

      try
      {
        document = LoadDocument(htmlContent);
      }
      catch (InvalidOperationException exc)
      {
        // sometimes SgmlReader doesn't handle <script> tags well and XDocument.Load() throws,
        // so we can retry with the html content with <script> tags stripped off

        if (!exc.Message.Contains("EndOfFile"))
        {
          throw;
        }

        htmlContent = HtmlUtils.RemoveScriptTags(htmlContent);

        document = LoadDocument(htmlContent);
      }

      return document;
    }

    private static XDocument LoadDocument(string htmlContent)
    {
      using (var sgmlReader = new SgmlReader())
      {
        sgmlReader.CaseFolding = CaseFolding.ToLower;
        sgmlReader.DocType = "HTML";
        sgmlReader.WhitespaceHandling = WhitespaceHandling.None;

        using (var sr = new StreamReader(new MemoryStream(Encoding.UTF8.GetBytes(htmlContent))))
        {
          sgmlReader.InputStream = sr;

          var document = XDocument.Load(sgmlReader);

          return document;
        }
      }
    }

    #endregion
  }
}
