/*
 * 
 * An XmlReader implementation for loading SGML (including HTML) converting it
 * to well formed XML, by adding missing quotes, empty attribute values, ignoring
 * duplicate attributes, case folding on tag names, adding missing closing tags
 * based on SGML DTD information, and so on.
 *
 * Copyright (c) 2002 Microsoft Corporation. All rights reserved. (Chris Lovett)
 *
 */

/*
 * 
 * Copyright (c) 2007-2013 MindTouch. All rights reserved.
 * www.mindtouch.com  oss@mindtouch.com
 *
 * For community documentation and downloads visit wiki.developer.mindtouch.com;
 * please review the licensing section.
 *
 * 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.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Reflection;
using System.Text;
using System.Xml;

namespace ReadSharp.Ports.Sgml
{
  /// <summary>
  /// SGML is case insensitive, so here you can choose between converting
  /// to lower case or upper case tags.  "None" means that the case is left
  /// alone, except that end tags will be folded to match the start tags.
  /// </summary>
  public enum CaseFolding
  {
    /// <summary>
    /// Do not convert case, except for converting end tags to match start tags.
    /// </summary>
    None,

    /// <summary>
    /// Convert tags to upper case.
    /// </summary>
    ToUpper,

    /// <summary>
    /// Convert tags to lower case.
    /// </summary>
    ToLower
  }

#if PORTABLE
  /// <summary>
  /// System.Xml.WhitespaceHandling is not available in .NETPortable.
  /// </summary>
  public enum WhitespaceHandling
  {
    All,
    None,
    Significant
  }
#endif

  /// <summary>
  /// This stack maintains a high water mark for allocated objects so the client
  /// can reuse the objects in the stack to reduce memory allocations, this is
  /// used to maintain current state of the parser for element stack, and attributes
  /// in each element.
  /// </summary>
  internal class HWStack
  {
    private object[] m_items;
    private int m_size;
    private int m_count;
    private int m_growth;

    /// <summary>
    /// Initialises a new instance of the HWStack class.
    /// </summary>
    /// <param name="growth">The amount to grow the stack space by, if more space is needed on the stack.</param>
    public HWStack(int growth)
    {
      this.m_growth = growth;
    }

    /// <summary>
    /// The number of items currently in the stack.
    /// </summary>
    public int Count
    {
      get
      {
        return this.m_count;
      }
      set
      {
        this.m_count = value;
      }
    }

    /// <summary>
    /// The size (capacity) of the stack.
    /// </summary>
    [SuppressMessage("Microsoft.Performance", "CA1811", Justification = "Kept for potential future usage.")]
    public int Size
    {
      get
      {
        return this.m_size;
      }
    }

    /// <summary>
    /// Returns the item at the requested index or null if index is out of bounds
    /// </summary>
    /// <param name="i">The index of the item to retrieve.</param>
    /// <returns>The item at the requested index or null if index is out of bounds.</returns>
    public object this[int i]
    {
      get
      {
        return (i >= 0 && i < this.m_size) ? m_items[i] : null;
      }
      set
      {
        this.m_items[i] = value;
      }
    }

    /// <summary>
    /// Removes and returns the item at the top of the stack
    /// </summary>
    /// <returns>The item at the top of the stack.</returns>
    public object Pop()
    {
      this.m_count--;
      if (this.m_count > 0)
      {
        return m_items[this.m_count - 1];
      }

      return null;
    }

    /// <summary>
    /// Pushes a new slot at the top of the stack.
    /// </summary>
    /// <returns>The object at the top of the stack.</returns>
    /// <remarks>
    /// This method tries to reuse a slot, if it returns null then
    /// the user has to call the other Push method.
    /// </remarks>
    public object Push()
    {
      if (this.m_count == this.m_size)
      {
        int newsize = this.m_size + this.m_growth;
        object[] newarray = new object[newsize];
        if (this.m_items != null)
          Array.Copy(this.m_items, newarray, this.m_size);

        this.m_size = newsize;
        this.m_items = newarray;
      }
      return m_items[this.m_count++];
    }

    /// <summary>
    /// Remove a specific item from the stack.
    /// </summary>
    /// <param name="i">The index of the item to remove.</param>
    [SuppressMessage("Microsoft.Performance", "CA1811", Justification = "Kept for potential future usage.")]
    public void RemoveAt(int i)
    {
      this.m_items[i] = null;
      Array.Copy(this.m_items, i + 1, this.m_items, i, this.m_count - i - 1);
      this.m_count--;
    }
  }

  /// <summary>
  /// This class represents an attribute.  The AttDef is assigned
  /// from a validation process, and is used to provide default values.
  /// </summary>
  internal class Attribute
  {
    internal string Name;    // the atomized name.
    internal AttDef DtdType; // the AttDef of the attribute from the SGML DTD.
    internal char QuoteChar; // the quote character used for the attribute value.
    private string m_literalValue; // the attribute value

    /// <summary>
    /// Attribute objects are reused during parsing to reduce memory allocations, 
    /// hence the Reset method.
    /// </summary>
    public void Reset(string name, string value, char quote)
    {
      this.Name = name;
      this.m_literalValue = value;
      this.QuoteChar = quote;
      this.DtdType = null;
    }

    public string Value
    {
      get
      {
        if (this.m_literalValue != null)
          return this.m_literalValue;
        if (this.DtdType != null)
          return this.DtdType.Default;
        return null;
      }
      /*            set
                  {
                      this.m_literalValue = value;
                  }*/
    }

    public bool IsDefault
    {
      get
      {
        return (this.m_literalValue == null);
      }
    }
  }

  /// <summary>
  /// This class models an XML node, an array of elements in scope is maintained while parsing
  /// for validation purposes, and these Node objects are reused to reduce object allocation,
  /// hence the reset method.  
  /// </summary>
  internal class Node
  {
    internal XmlNodeType NodeType;
    internal string Value;
    internal XmlSpace Space;
    internal string XmlLang;
    internal bool IsEmpty;
    internal string Name;
    internal ElementDecl DtdType; // the DTD type found via validation
    internal State CurrentState;
    internal bool Simulated; // tag was injected into result stream.
    HWStack attributes = new HWStack(10);

    /// <summary>
    /// Attribute objects are reused during parsing to reduce memory allocations, 
    /// hence the Reset method. 
    /// </summary>
    public void Reset(string name, XmlNodeType nt, string value)
    {
      this.Value = value;
      this.Name = name;
      this.NodeType = nt;
      this.Space = XmlSpace.None;
      this.XmlLang = null;
      this.IsEmpty = true;
      this.attributes.Count = 0;
      this.DtdType = null;
    }

    public Attribute AddAttribute(string name, string value, char quotechar, bool caseInsensitive)
    {
      Attribute a;
      // check for duplicates!
      for (int i = 0, n = this.attributes.Count; i < n; i++)
      {
        a = (Attribute)this.attributes[i];
        if (string.Equals(a.Name, name, caseInsensitive ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal))
        {
          return null;
        }
      }
      // This code makes use of the high water mark for attribute objects,
      // and reuses exisint Attribute objects to avoid memory allocation.
      a = (Attribute)this.attributes.Push();
      if (a == null)
      {
        a = new Attribute();
        this.attributes[this.attributes.Count - 1] = a;
      }
      a.Reset(name, value, quotechar);
      return a;
    }

    [SuppressMessage("Microsoft.Performance", "CA1811", Justification = "Kept for potential future usage.")]
    public void RemoveAttribute(string name)
    {
      for (int i = 0, n = this.attributes.Count; i < n; i++)
      {
        Attribute a = (Attribute)this.attributes[i];
        if (string.Equals(a.Name, name, StringComparison.OrdinalIgnoreCase))
        {
          this.attributes.RemoveAt(i);
          return;
        }
      }
    }
    public void CopyAttributes(Node n)
    {
      for (int i = 0, len = n.attributes.Count; i < len; i++)
      {
        Attribute a = (Attribute)n.attributes[i];
        Attribute na = this.AddAttribute(a.Name, a.Value, a.QuoteChar, false);
        na.DtdType = a.DtdType;
      }
    }

    public int AttributeCount
    {
      get
      {
        return this.attributes.Count;
      }
    }

    public int GetAttribute(string name)
    {
      for (int i = 0, n = this.attributes.Count; i < n; i++)
      {
        Attribute a = (Attribute)this.attributes[i];
        if (string.Equals(a.Name, name, StringComparison.OrdinalIgnoreCase))
        {
          return i;
        }
      }
      return -1;
    }

    public Attribute GetAttribute(int i)
    {
      if (i >= 0 && i < this.attributes.Count)
      {
        Attribute a = (Attribute)this.attributes[i];
        return a;
      }
      return null;
    }
  }

  internal enum State
  {
    Initial,    // The initial state (Read has not been called yet)
    Markup,     // Expecting text or markup
    EndTag,     // Positioned on an end tag
    Attr,       // Positioned on an attribute
    AttrValue,  // Positioned in an attribute value
    Text,       // Positioned on a Text node.
    PartialTag, // Positioned on a text node, and we have hit a start tag
    AutoClose,  // We are auto-closing tags (this is like State.EndTag), but end tag was generated
    CData,      // We are on a CDATA type node, eg. <scipt> where we have special parsing rules.
    PartialText,
    PseudoStartTag, // we pushed a pseudo-start tag, need to continue with previous start tag.
    Eof
  }


  /// <summary>
  /// SgmlReader is an XmlReader API over any SGML document (including built in 
  /// support for HTML).  
  /// </summary>
  public class SgmlReader : XmlReader
  {
    /// <summary>
    /// The value returned when a namespace is queried and none has been specified.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1705", Justification = "SgmlReader's standards for constants are different to Microsoft's and in line with older C++ style constants naming conventions.  Visually, constants using this style are more easily identifiable as such.")]
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1707", Justification = "SgmlReader's standards for constants are different to Microsoft's and in line with older C++ style constants naming conventions.  Visually, constants using this style are more easily identifiable as such.")]
    public const string UNDEFINED_NAMESPACE = "#unknown";

    private SgmlDtd m_dtd;
    private Entity m_current;
    private State m_state;
    private char m_partial;
    private string m_endTag;
    private HWStack m_stack;
    private Node m_node; // current node (except for attributes)
    // Attributes are handled separately using these members.
    private Attribute m_a;
    private int m_apos; // which attribute are we positioned on in the collection.
    private Uri m_baseUri;
    private StringBuilder m_sb;
    private StringBuilder m_name;
    private TextWriter m_log;
    private bool m_foundRoot;
    private bool m_ignoreDtd;

    // autoclose support
    private Node m_newnode;
    private int m_poptodepth;
    private int m_rootCount;
    private bool m_isHtml;
    private string m_rootElementName;

    private string m_href;
    private Entity m_lastError;
    private string m_proxy;
    private TextReader m_inputStream;
    private string m_syslit;
    private string m_pubid;
    private string m_subset;
    private string m_docType;
    private WhitespaceHandling m_whitespaceHandling;
    private CaseFolding m_folding = CaseFolding.None;
    private bool m_stripDocType = true;
    //private string m_startTag;
    private Dictionary<string, string> unknownNamespaces = new Dictionary<string, string>();

    /// <summary>
    /// Initialises a new instance of the SgmlReader class.
    /// </summary>
    public SgmlReader()
    {
      Init();
    }

    /// <summary>
    /// Initialises a new instance of the SgmlReader class with an existing <see cref="XmlNameTable"/>, which is NOT used.
    /// </summary>
    /// <param name="nt">The nametable to use.</param>
    public SgmlReader(XmlNameTable nt)
    {
      Init();
    }

    /// <summary>
    /// Specify the SgmlDtd object directly.  This allows you to cache the Dtd and share
    /// it across multipl SgmlReaders.  To load a DTD from a URL use the SystemLiteral property.
    /// </summary>
    public SgmlDtd Dtd
    {
      get
      {
        if (this.m_dtd == null)
        {
          LazyLoadDtd(this.m_baseUri);
        }

        return this.m_dtd;
      }
      set
      {
        this.m_dtd = value;
      }
    }

    private void LazyLoadDtd(Uri baseUri)
    {
      if (this.m_dtd == null && !this.m_ignoreDtd)
      {
        if (string.IsNullOrEmpty(this.m_syslit))
        {
          if (this.m_docType != null && StringUtilities.EqualsIgnoreCase(this.m_docType, "html"))
          {
            Assembly a = typeof(SgmlReader).GetTypeInfo().Assembly;
            string name = a.FullName.Split(',')[0] + ".Html.dtd";
            Stream stm = a.GetManifestResourceStream(name);
            if (stm != null)
            {
              StreamReader sr = new StreamReader(stm);
              this.m_dtd = SgmlDtd.Parse(baseUri, "HTML", sr, null, this.m_proxy, null);
            }
          }
        }
        else
        {
          if (baseUri != null)
          {
            baseUri = new Uri(baseUri, this.m_syslit);
          }
          else if (this.m_baseUri != null)
          {
            baseUri = new Uri(this.m_baseUri, this.m_syslit);
          }
          else
          {
#if PORTABLE
            throw new InvalidOperationException("Cannot load DTD without specifying base URI.");
#else
                        baseUri = new Uri(new Uri(Directory.GetCurrentDirectory() + "/"), this.m_syslit);
#endif
          }
          this.m_dtd = SgmlDtd.Parse(baseUri, this.m_docType, this.m_pubid, baseUri.AbsoluteUri, this.m_subset, this.m_proxy, null);
        }
      }

      if (this.m_dtd != null && this.m_dtd.Name != null)
      {
        switch (this.CaseFolding)
        {
          case CaseFolding.ToUpper:
            this.m_rootElementName = this.m_dtd.Name.ToUpperInvariant();
            break;
          case CaseFolding.ToLower:
            this.m_rootElementName = this.m_dtd.Name.ToLowerInvariant();
            break;
          default:
            this.m_rootElementName = this.m_dtd.Name;
            break;
        }

        this.m_isHtml = StringUtilities.EqualsIgnoreCase(this.m_dtd.Name, "html");
      }
    }

    /// <summary>
    /// The name of root element specified in the DOCTYPE tag.
    /// </summary>
    public string DocType
    {
      get
      {
        return this.m_docType;
      }
      set
      {
        this.m_docType = value;
      }
    }

    /// <summary>
    /// The root element of the document.
    /// </summary>
    public string RootElementName
    {
      get
      {
        return m_rootElementName;
      }
    }

    /// <summary>
    /// The PUBLIC identifier in the DOCTYPE tag
    /// </summary>
    public string PublicIdentifier
    {
      get
      {
        return this.m_pubid;
      }
      set
      {
        this.m_pubid = value;
      }
    }

    /// <summary>
    /// The SYSTEM literal in the DOCTYPE tag identifying the location of the DTD.
    /// </summary>
    public string SystemLiteral
    {
      get
      {
        return this.m_syslit;
      }
      set
      {
        this.m_syslit = value;
      }
    }

    /// <summary>
    /// The DTD internal subset in the DOCTYPE tag
    /// </summary>
    public string InternalSubset
    {
      get
      {
        return this.m_subset;
      }
      set
      {
        this.m_subset = value;
      }
    }

    /// <summary>
    /// The input stream containing SGML data to parse.
    /// You must specify this property or the Href property before calling Read().
    /// </summary>
    public TextReader InputStream
    {
      get
      {
        return this.m_inputStream;
      }
      set
      {
        this.m_inputStream = value;
        Init();
      }
    }

    /// <summary>
    /// Sometimes you need to specify a proxy server in order to load data via HTTP
    /// from outside the firewall.  For example: "itgproxy:80".
    /// </summary>
    public string WebProxy
    {
      get
      {
        return this.m_proxy;
      }
      set
      {
        this.m_proxy = value;
      }
    }

    /// <summary>
    /// The base Uri is used to resolve relative Uri's like the SystemLiteral and
    /// Href properties.  This is a method because BaseURI is a read-only
    /// property on the base XmlReader class.
    /// </summary>
    public void SetBaseUri(string uri)
    {
      this.m_baseUri = new Uri(uri);
    }

    /// <summary>
    /// Specify the location of the input SGML document as a URL.
    /// </summary>
    public string Href
    {
      get
      {
        return this.m_href;
      }
      set
      {
        this.m_href = value;
        Init();
        if (this.m_baseUri == null)
        {
          if (this.m_href.IndexOf("://") > 0)
          {
            this.m_baseUri = new Uri(this.m_href);
          }
          else
          {
#if PORTABLE
            throw new ArgumentException("Relative URLs are not supported.");
#else
                        this.m_baseUri = new Uri("file:///" + Directory.GetCurrentDirectory() + "//");
#endif
          }
        }
      }
    }

    /// <summary>
    /// Whether to strip out the DOCTYPE tag from the output (default true)
    /// </summary>
    public bool StripDocType
    {
      get
      {
        return this.m_stripDocType;
      }
      set
      {
        this.m_stripDocType = value;
      }
    }

    /// <summary>
    /// Gets or sets a value indicating whether to ignore any DTD reference.
    /// </summary>
    /// <value><c>true</c> if DTD references should be ignored; otherwise, <c>false</c>.</value>
    public bool IgnoreDtd
    {
      get { return m_ignoreDtd; }
      set { m_ignoreDtd = value; }
    }

    /// <summary>
    /// The case conversion behaviour while processing tags.
    /// </summary>
    public CaseFolding CaseFolding
    {
      get
      {
        return this.m_folding;
      }
      set
      {
        this.m_folding = value;
      }
    }

    /// <summary>
    /// DTD validation errors are written to this stream.
    /// </summary>
    public TextWriter ErrorLog
    {
      get
      {
        return this.m_log;
      }
      set
      {
        this.m_log = value;
      }
    }

    /// <summary>
    /// DTD validation errors are written to this log file.
    /// </summary>
#if PORTABLE
    [Obsolete("Not supported on the .NETPortable runtime.")]
#endif
    public string ErrorLogFile
    {
#if PORTABLE
      get
      {
        throw new NotSupportedException();
      }
      set
      {
        throw new NotSupportedException();
      }
#else
            get
            {
                return this.m_errorLogFile;
            }
            set
            {
                this.m_errorLogFile = value;
                this.m_log = new StreamWriter(value);
            }
#endif
    }

    private void Log(string msg, params string[] args)
    {
      if (ErrorLog != null)
      {
        string err = string.Format(CultureInfo.CurrentUICulture, msg, args);
        if (this.m_lastError != this.m_current)
        {
          err = err + "    " + this.m_current.Context();
          this.m_lastError = this.m_current;
          ErrorLog.WriteLine("### Error:" + err);
        }
        else
        {
          string path = "";
          if (this.m_current.ResolvedUri != null)
          {
            path = this.m_current.ResolvedUri.AbsolutePath;
          }

          ErrorLog.WriteLine("### Error in {0}#{1}, line {2}, position {3}: {4}", path, this.m_current.Name, this.m_current.Line, this.m_current.LinePosition, err);
        }
      }
    }

    private void Log(string msg, char ch)
    {
      Log(msg, ch.ToString());
    }

    private void Init()
    {
      this.m_state = State.Initial;
      this.m_stack = new HWStack(10);
      this.m_node = Push(null, XmlNodeType.Document, null);
      this.m_node.IsEmpty = false;
      this.m_sb = new StringBuilder();
      this.m_name = new StringBuilder();
      this.m_poptodepth = 0;
      this.m_current = null;
      this.m_partial = '\0';
      this.m_endTag = null;
      this.m_a = null;
      this.m_apos = 0;
      this.m_newnode = null;
      this.m_rootCount = 0;
      this.m_foundRoot = false;
      this.unknownNamespaces.Clear();
    }

    private Node Push(string name, XmlNodeType nt, string value)
    {
      Node result = (Node)this.m_stack.Push();
      if (result == null)
      {
        result = new Node();
        this.m_stack[this.m_stack.Count - 1] = result;
      }

      result.Reset(name, nt, value);
      this.m_node = result;
      return result;
    }

    private void SwapTopNodes()
    {
      int top = this.m_stack.Count - 1;
      if (top > 0)
      {
        Node n = (Node)this.m_stack[top - 1];
        this.m_stack[top - 1] = this.m_stack[top];
        this.m_stack[top] = n;
      }
    }

    private Node Push(Node n)
    {
      // we have to do a deep clone of the Node object because
      // it is reused in the stack.
      Node n2 = Push(n.Name, n.NodeType, n.Value);
      n2.DtdType = n.DtdType;
      n2.IsEmpty = n.IsEmpty;
      n2.Space = n.Space;
      n2.XmlLang = n.XmlLang;
      n2.CurrentState = n.CurrentState;
      n2.CopyAttributes(n);
      this.m_node = n2;
      return n2;
    }

    private void Pop()
    {
      if (this.m_stack.Count > 1)
      {
        this.m_node = (Node)this.m_stack.Pop();
      }
    }

    private Node Top()
    {
      int top = this.m_stack.Count - 1;
      if (top > 0)
      {
        return (Node)this.m_stack[top];
      }

      return null;
    }

    /// <summary>
    /// The node type of the node currently being parsed.
    /// </summary>
    public override XmlNodeType NodeType
    {
      get
      {
        if (this.m_state == State.Attr)
        {
          return XmlNodeType.Attribute;
        }
        else if (this.m_state == State.AttrValue)
        {
          return XmlNodeType.Text;
        }
        else if (this.m_state == State.EndTag || this.m_state == State.AutoClose)
        {
          return XmlNodeType.EndElement;
        }

        return this.m_node.NodeType;
      }
    }

    /// <summary>
    /// The name of the current node, if currently positioned on a node or attribute.
    /// </summary>
    public override string Name
    {
      get
      {
        string result = null;
        if (this.m_state == State.Attr)
        {
          result = XmlConvert.EncodeName(this.m_a.Name);
        }
        else if (this.m_state != State.AttrValue)
        {
          result = this.m_node.Name;
        }

        return result;
      }
    }

    /// <summary>
    /// The local name of the current node, if currently positioned on a node or attribute.
    /// </summary>
    public override string LocalName
    {
      get
      {
        string result = Name;
        if (result != null)
        {
          int colon = result.IndexOf(':');
          if (colon != -1)
          {
            result = result.Substring(colon + 1);
          }
        }
        return result;
      }
    }

    /// <summary>
    /// The namespace of the current node, if currently positioned on a node or attribute.
    /// </summary>
    /// <remarks>
    /// If not positioned on a node or attribute, <see cref="UNDEFINED_NAMESPACE"/> is returned.
    /// </remarks>
    [SuppressMessage("Microsoft.Performance", "CA1820", Justification = "Cannot use IsNullOrEmpty in a switch statement and swapping the elegance of switch for a load of 'if's is not worth it.")]
    public override string NamespaceURI
    {
      get
      {
        // SGML has no namespaces, unless this turned out to be an xmlns attribute.
        if (this.m_state == State.Attr && string.Equals(this.m_a.Name, "xmlns", StringComparison.OrdinalIgnoreCase))
        {
          return "http://www.w3.org/2000/xmlns/";
        }

        string prefix = Prefix;
        switch (Prefix)
        {
          case "xmlns":
            return "http://www.w3.org/2000/xmlns/";
          case "xml":
            return "http://www.w3.org/XML/1998/namespace";
          case null: // Should never occur since Prefix never returns null
          case "":
            if (NodeType == XmlNodeType.Attribute)
            {
              // attributes without a prefix are never in any namespace
              return string.Empty;
            }
            else if (NodeType == XmlNodeType.Element)
            {
              // check if a 'xmlns:prefix' attribute is defined
              for (int i = this.m_stack.Count - 1; i > 0; --i)
              {
                Node node = this.m_stack[i] as Node;
                if ((node != null) && (node.NodeType == XmlNodeType.Element))
                {
                  int index = node.GetAttribute("xmlns");
                  if (index >= 0)
                  {
                    string value = node.GetAttribute(index).Value;
                    if (value != null)
                    {
                      return value;
                    }
                  }
                }
              }
            }

            return string.Empty;
          default:
            {
              string value;
              if ((NodeType == XmlNodeType.Attribute) || (NodeType == XmlNodeType.Element))
              {

                // check if a 'xmlns:prefix' attribute is defined
                string key = "xmlns:" + prefix;
                for (int i = this.m_stack.Count - 1; i > 0; --i)
                {
                  Node node = this.m_stack[i] as Node;
                  if ((node != null) && (node.NodeType == XmlNodeType.Element))
                  {
                    int index = node.GetAttribute(key);
                    if (index >= 0)
                    {
                      value = node.GetAttribute(index).Value;
                      if (value != null)
                      {
                        return value;
                      }
                    }
                  }
                }
              }

              // check if we've seen this prefix before
              if (!unknownNamespaces.TryGetValue(prefix, out value))
              {
                if (unknownNamespaces.Count > 0)
                {
                  value = UNDEFINED_NAMESPACE + unknownNamespaces.Count.ToString();
                }
                else
                {
                  value = UNDEFINED_NAMESPACE;
                }
                unknownNamespaces[prefix] = value;
              }
              return value;
            }
        }
      }
    }

    /// <summary>
    /// The prefix of the current node's name.
    /// </summary>
    public override string Prefix
    {
      get
      {
        string result = Name;
        if (result != null)
        {
          int colon = result.IndexOf(':');
          if (colon != -1)
          {
            result = result.Substring(0, colon);
          }
          else
          {
            result = string.Empty;
          }
        }
        return result ?? string.Empty;
      }
    }

    /// <summary>
    /// Whether the current node has a value or not.
    /// </summary>
    public override bool HasValue
    {
      get
      {
        if (this.m_state == State.Attr || this.m_state == State.AttrValue)
        {
          return true;
        }

        return (this.m_node.Value != null);
      }
    }

    /// <summary>
    /// The value of the current node.
    /// </summary>
    public override string Value
    {
      get
      {
        if (this.m_state == State.Attr || this.m_state == State.AttrValue)
        {
          return this.m_a.Value;
        }

        return this.m_node.Value;
      }
    }

    /// <summary>
    /// Gets the depth of the current node in the XML document.
    /// </summary>
    /// <value>The depth of the current node in the XML document.</value>
    public override int Depth
    {
      get
      {
        if (this.m_state == State.Attr)
        {
          return this.m_stack.Count;
        }
        else if (this.m_state == State.AttrValue)
        {
          return this.m_stack.Count + 1;
        }

        return this.m_stack.Count - 1;
      }
    }

    /// <summary>
    /// Gets the base URI of the current node.
    /// </summary>
    /// <value>The base URI of the current node.</value>
    public override string BaseURI
    {
      get
      {
        return this.m_baseUri == null ? "" : this.m_baseUri.AbsoluteUri;
      }
    }

    /// <summary>
    /// Gets a value indicating whether the current node is an empty element (for example, &lt;MyElement/&gt;).
    /// </summary>
    public override bool IsEmptyElement
    {
      get
      {
        if (this.m_state == State.Markup || this.m_state == State.Attr || this.m_state == State.AttrValue)
        {
          return this.m_node.IsEmpty;
        }

        return false;
      }
    }

    /// <summary>
    /// Gets a value indicating whether the current node is an attribute that was generated from the default value defined in the DTD or schema.
    /// </summary>
    /// <value>
    /// true if the current node is an attribute whose value was generated from the default value defined in the DTD or
    /// schema; false if the attribute value was explicitly set.
    /// </value>
    public override bool IsDefault
    {
      get
      {
        if (this.m_state == State.Attr || this.m_state == State.AttrValue)
          return this.m_a.IsDefault;

        return false;
      }
    }

    /// <summary>
    /// Gets the quotation mark character used to enclose the value of an attribute node.
    /// </summary>
    /// <value>The quotation mark character (" or ') used to enclose the value of an attribute node.</value>
    /// <remarks>
    /// This property applies only to an attribute node.
    /// </remarks>
#if PORTABLE
    public char QuoteChar
#else
        public override char QuoteChar
#endif
    {
      get
      {
        if (this.m_a != null)
          return this.m_a.QuoteChar;

        return '\0';
      }
    }

    /// <summary>
    /// Gets the current xml:space scope.
    /// </summary>
    /// <value>One of the <see cref="XmlSpace"/> values. If no xml:space scope exists, this property defaults to XmlSpace.None.</value>
    public override XmlSpace XmlSpace
    {
      get
      {
        for (int i = this.m_stack.Count - 1; i > 1; i--)
        {
          Node n = (Node)this.m_stack[i];
          XmlSpace xs = n.Space;
          if (xs != XmlSpace.None)
            return xs;
        }

        return XmlSpace.None;
      }
    }

    /// <summary>
    /// Gets the current xml:lang scope.
    /// </summary>
    /// <value>The current xml:lang scope.</value>
    public override string XmlLang
    {
      get
      {
        for (int i = this.m_stack.Count - 1; i > 1; i--)
        {
          Node n = (Node)this.m_stack[i];
          string xmllang = n.XmlLang;
          if (xmllang != null)
            return xmllang;
        }

        return string.Empty;
      }
    }

    /// <summary>
    /// Specifies how white space is handled.
    /// </summary>
    public WhitespaceHandling WhitespaceHandling
    {
      get
      {
        return this.m_whitespaceHandling;
      }
      set
      {
        this.m_whitespaceHandling = value;
      }
    }

    /// <summary>
    /// Gets the number of attributes on the current node.
    /// </summary>
    /// <value>The number of attributes on the current node.</value>
    public override int AttributeCount
    {
      get
      {
        if (this.m_state == State.Attr || this.m_state == State.AttrValue)
          //For compatibility with mono
          return this.m_node.AttributeCount;
        else if (this.m_node.NodeType == XmlNodeType.Element || this.m_node.NodeType == XmlNodeType.DocumentType)
          return this.m_node.AttributeCount;
        else
          return 0;
      }
    }

    /// <summary>
    /// Gets the value of an attribute with the specified <see cref="Name"/>.
    /// </summary>
    /// <param name="name">The name of the attribute to retrieve.</param>
    /// <returns>The value of the specified attribute. If the attribute is not found, a null reference (Nothing in Visual Basic) is returned. </returns>
    public override string GetAttribute(string name)
    {
      if (this.m_state != State.Attr && this.m_state != State.AttrValue)
      {
        int i = this.m_node.GetAttribute(name);
        if (i >= 0)
          return GetAttribute(i);
      }

      return null;
    }

    /// <summary>
    /// Gets the value of the attribute with the specified <see cref="LocalName"/> and <see cref="NamespaceURI"/>.
    /// </summary>
    /// <param name="name">The local name of the attribute.</param>
    /// <param name="namespaceURI">The namespace URI of the attribute.</param>
    /// <returns>The value of the specified attribute. If the attribute is not found, a null reference (Nothing in Visual Basic) is returned. This method does not move the reader.</returns>
    public override string GetAttribute(string name, string namespaceURI)
    {
      return GetAttribute(name); // SGML has no namespaces.
    }

    /// <summary>
    /// Gets the value of the attribute with the specified index.
    /// </summary>
    /// <param name="i">The index of the attribute.</param>
    /// <returns>The value of the specified attribute. This method does not move the reader.</returns>
    public override string GetAttribute(int i)
    {
      if (this.m_state != State.Attr && this.m_state != State.AttrValue)
      {
        Attribute a = this.m_node.GetAttribute(i);
        if (a != null)
          return a.Value;
      }

      throw new ArgumentOutOfRangeException("i");
    }

    /// <summary>
    /// Gets the value of the attribute with the specified index.
    /// </summary>
    /// <param name="i">The index of the attribute.</param>
    /// <returns>The value of the specified attribute. This method does not move the reader.</returns>
    public override string this[int i]
    {
      get
      {
        return GetAttribute(i);
      }
    }

    /// <summary>
    /// Gets the value of an attribute with the specified <see cref="Name"/>.
    /// </summary>
    /// <param name="name">The name of the attribute to retrieve.</param>
    /// <returns>The value of the specified attribute. If the attribute is not found, a null reference (Nothing in Visual Basic) is returned. </returns>
    public override string this[string name]
    {
      get
      {
        return GetAttribute(name);
      }
    }

    /// <summary>
    /// Gets the value of the attribute with the specified <see cref="LocalName"/> and <see cref="NamespaceURI"/>.
    /// </summary>
    /// <param name="name">The local name of the attribute.</param>
    /// <param name="namespaceURI">The namespace URI of the attribute.</param>
    /// <returns>The value of the specified attribute. If the attribute is not found, a null reference (Nothing in Visual Basic) is returned. This method does not move the reader.</returns>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1023", Justification = "This design is that of Microsoft's XmlReader class and overriding its method is merely continuing the same design.")]
    public override string this[string name, string namespaceURI]
    {
      get
      {
        return GetAttribute(name, namespaceURI);
      }
    }

    /// <summary>
    /// Moves to the atttribute with the specified <see cref="Name"/>.
    /// </summary>
    /// <param name="name">The qualified name of the attribute.</param>
    /// <returns>true if the attribute is found; otherwise, false. If false, the reader's position does not change.</returns>
    public override bool MoveToAttribute(string name)
    {
      int i = this.m_node.GetAttribute(name);
      if (i >= 0)
      {
        MoveToAttribute(i);
        return true;
      }

      return false;
    }

    /// <summary>
    /// Moves to the attribute with the specified <see cref="LocalName"/> and <see cref="NamespaceURI"/>.
    /// </summary>
    /// <param name="name">The local name of the attribute.</param>
    /// <param name="ns">The namespace URI of the attribute.</param>
    /// <returns>true if the attribute is found; otherwise, false. If false, the reader's position does not change.</returns>
    public override bool MoveToAttribute(string name, string ns)
    {
      return MoveToAttribute(name);
    }

    /// <summary>
    /// Moves to the attribute with the specified index.
    /// </summary>
    /// <param name="i">The index of the attribute to move to.</param>
    public override void MoveToAttribute(int i)
    {
      Attribute a = this.m_node.GetAttribute(i);
      if (a != null)
      {
        this.m_apos = i;
        this.m_a = a;
        //Make sure that AttrValue does not overwrite the preserved value
        if (this.m_state != State.Attr && this.m_state != State.AttrValue)
        {
          this.m_node.CurrentState = this.m_state; //save current state.
        }

        this.m_state = State.Attr;
        return;
      }

      throw new ArgumentOutOfRangeException("i");
    }

    /// <summary>
    /// Moves to the first attribute.
    /// </summary>
    /// <returns></returns>
    public override bool MoveToFirstAttribute()
    {
      if (this.m_node.AttributeCount > 0)
      {
        MoveToAttribute(0);
        return true;
      }

      return false;
    }

    /// <summary>
    /// Moves to the next attribute.
    /// </summary>
    /// <returns>true if there is a next attribute; false if there are no more attributes.</returns>
    /// <remarks>
    /// If the current node is an element node, this method is equivalent to <see cref="MoveToFirstAttribute"/>. If <see cref="MoveToNextAttribute"/> returns true,
    /// the reader moves to the next attribute; otherwise, the position of the reader does not change.
    /// </remarks>
    public override bool MoveToNextAttribute()
    {
      if (this.m_state != State.Attr && this.m_state != State.AttrValue)
      {
        return MoveToFirstAttribute();
      }
      else if (this.m_apos < this.m_node.AttributeCount - 1)
      {
        MoveToAttribute(this.m_apos + 1);
        return true;
      }
      else
        return false;
    }

    /// <summary>
    /// Moves to the element that contains the current attribute node.
    /// </summary>
    /// <returns>
    /// true if the reader is positioned on an attribute (the reader moves to the element that owns the attribute); false if the reader is not positioned
    /// on an attribute (the position of the reader does not change).
    /// </returns>
    public override bool MoveToElement()
    {
      if (this.m_state == State.Attr || this.m_state == State.AttrValue)
      {
        this.m_state = this.m_node.CurrentState;
        this.m_a = null;
        return true;
      }
      else
        return (this.m_node.NodeType == XmlNodeType.Element);
    }

    /// <summary>
    /// Gets whether the content is HTML or not.
    /// </summary>
    public bool IsHtml
    {
      get
      {
        return this.m_isHtml;
      }
    }

    /// <summary>
    /// Returns the encoding of the current entity.
    /// </summary>
    /// <returns>The encoding of the current entity.</returns>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1024", Justification = "This method to get the encoding does not simply read a value, but potentially causes significant processing of the input stream.")]
    public Encoding GetEncoding()
    {
      if (this.m_current == null)
      {
        OpenInput();
      }

      return this.m_current.Encoding;
    }

    private void OpenInput()
    {
      LazyLoadDtd(this.m_baseUri);

      if (this.Href != null)
      {
        this.m_current = new Entity("#document", null, this.m_href, this.m_proxy);
      }
      else if (this.m_inputStream != null)
      {
        this.m_current = new Entity("#document", null, this.m_inputStream, this.m_proxy);
      }
      else
      {
        throw new InvalidOperationException("You must specify input either via Href or InputStream properties");
      }

      this.m_current.IsHtml = this.IsHtml;
      this.m_current.Open(null, this.m_baseUri);
      if (this.m_current.ResolvedUri != null)
        this.m_baseUri = this.m_current.ResolvedUri;

      if (this.m_current.IsHtml && this.m_dtd == null)
      {
        this.m_docType = "HTML";
        LazyLoadDtd(this.m_baseUri);
      }
    }

    /// <summary>
    /// Reads the next node from the stream.
    /// </summary>
    /// <returns>true if the next node was read successfully; false if there are no more nodes to read.</returns>
    public override bool Read()
    {
      if (m_current == null)
      {
        OpenInput();
      }

      if (m_node.Simulated)
      {
        // return the next node
        m_node.Simulated = false;
        this.m_node = Top();
        this.m_state = this.m_node.CurrentState;
        return true;
      }

      bool foundnode = false;
      while (!foundnode)
      {
        switch (this.m_state)
        {
          case State.Initial:
            this.m_state = State.Markup;
            this.m_current.ReadChar();
            goto case State.Markup;
          case State.Eof:
            if (this.m_current.Parent != null)
            {
              this.m_current.Close();
              this.m_current = this.m_current.Parent;
            }
            else
            {
              return false;
            }
            break;
          case State.EndTag:
            if (string.Equals(this.m_endTag, this.m_node.Name, StringComparison.OrdinalIgnoreCase))
            {
              Pop(); // we're done!
              this.m_state = State.Markup;
              goto case State.Markup;
            }
            Pop(); // close one element
            foundnode = true;// return another end element.
            break;
          case State.Markup:
            if (this.m_node.IsEmpty)
            {
              Pop();
            }
            foundnode = ParseMarkup();
            break;
          case State.PartialTag:
            Pop(); // remove text node.
            this.m_state = State.Markup;
            foundnode = ParseTag(this.m_partial);
            break;
          case State.PseudoStartTag:
            foundnode = ParseStartTag('<');
            break;
          case State.AutoClose:
            Pop(); // close next node.
            if (this.m_stack.Count <= this.m_poptodepth)
            {
              this.m_state = State.Markup;
              if (this.m_newnode != null)
              {
                Push(this.m_newnode); // now we're ready to start the new node.
                this.m_newnode = null;
                this.m_state = State.Markup;
              }
              else if (this.m_node.NodeType == XmlNodeType.Document)
              {
                this.m_state = State.Eof;
                goto case State.Eof;
              }
            }
            foundnode = true;
            break;
          case State.CData:
            foundnode = ParseCData();
            break;
          case State.Attr:
            goto case State.AttrValue;
          case State.AttrValue:
            this.m_state = State.Markup;
            goto case State.Markup;
          case State.Text:
            Pop();
            goto case State.Markup;
          case State.PartialText:
            if (ParseText(this.m_current.Lastchar, false))
            {
              this.m_node.NodeType = XmlNodeType.Whitespace;
            }

            foundnode = true;
            break;
        }

        if (foundnode && this.m_node.NodeType == XmlNodeType.Whitespace && this.m_whitespaceHandling == WhitespaceHandling.None)
        {
          // strip out whitespace (caller is probably pretty printing the XML).
          foundnode = false;
        }
        if (!foundnode && this.m_state == State.Eof && this.m_stack.Count > 1)
        {
          this.m_poptodepth = 1;
          this.m_state = State.AutoClose;
          this.m_node = Top();
          return true;
        }
      }
      if (!m_foundRoot && (this.NodeType == XmlNodeType.Element ||
              this.NodeType == XmlNodeType.Text ||
              this.NodeType == XmlNodeType.CDATA))
      {
        m_foundRoot = true;
        if (this.IsHtml && (this.NodeType != XmlNodeType.Element ||
            !string.Equals(this.LocalName, "html", StringComparison.OrdinalIgnoreCase)))
        {
          // Simulate an HTML root element!
          this.m_node.CurrentState = this.m_state;
          Node root = Push("html", XmlNodeType.Element, null);
          SwapTopNodes(); // make html the outer element.
          this.m_node = root;
          root.Simulated = true;
          root.IsEmpty = false;
          this.m_state = State.Markup;
          //this.state = State.PseudoStartTag;
          //this.startTag = name;
        }

        return true;
      }

      return true;
    }

    private bool ParseMarkup()
    {
      char ch = this.m_current.Lastchar;
      if (ch == '<')
      {
        ch = this.m_current.ReadChar();
        return ParseTag(ch);
      }
      else if (ch != Entity.EOF)
      {
        if (this.m_node.DtdType != null && this.m_node.DtdType.ContentModel.DeclaredContent == DeclaredContent.CDATA)
        {
          // e.g. SCRIPT or STYLE tags which contain unparsed character data.
          this.m_partial = '\0';
          this.m_state = State.CData;
          return false;
        }
        else if (ParseText(ch, true))
        {
          this.m_node.NodeType = XmlNodeType.Whitespace;
        }

        return true;
      }

      this.m_state = State.Eof;
      return false;
    }

    private const string declterm = " \t\r\n><";
    private bool ParseTag(char ch)
    {
      if (ch == '%')
      {
        return ParseAspNet();
      }
      else if (ch == '!')
      {
        ch = this.m_current.ReadChar();
        if (ch == '-')
        {
          return ParseComment();
        }
        else if (ch == '[')
        {
          return ParseConditionalBlock();
        }
        else if (ch != '_' && !char.IsLetter(ch))
        {
          // perhaps it's one of those nasty office document hacks like '<![if ! ie ]>'
          string value = this.m_current.ScanToEnd(this.m_sb, "Recovering", ">"); // skip it
          Log("Ignoring invalid markup '<!" + value + ">");
          return false;
        }
        else
        {
          string name = this.m_current.ScanToken(this.m_sb, SgmlReader.declterm, false);
          if (string.Equals(name, "DOCTYPE", StringComparison.OrdinalIgnoreCase))
          {
            ParseDocType();

            // In SGML DOCTYPE SYSTEM attribute is optional, but in XML it is required,
            // therefore if there is no SYSTEM literal then add an empty one.
            if (this.GetAttribute("SYSTEM") == null && this.GetAttribute("PUBLIC") != null)
            {
              this.m_node.AddAttribute("SYSTEM", "", '"', this.m_folding == CaseFolding.None);
            }

            if (m_stripDocType)
            {
              return false;
            }
            else
            {
              this.m_node.NodeType = XmlNodeType.DocumentType;
              return true;
            }
          }
          else
          {
            Log("Invalid declaration '<!{0}...'.  Expecting '<!DOCTYPE' only.", name);
            this.m_current.ScanToEnd(null, "Recovering", ">"); // skip it
            return false;
          }
        }
      }
      else if (ch == '?')
      {
        this.m_current.ReadChar();// consume the '?' character.
        return ParsePI();
      }
      else if (ch == '/')
      {
        return ParseEndTag();
      }
      else
      {
        return ParseStartTag(ch);
      }
    }

    private string ScanName(string terminators)
    {
      string name = this.m_current.ScanToken(this.m_sb, terminators, false);
      switch (this.m_folding)
      {
        case CaseFolding.ToUpper:
          name = name.ToUpperInvariant();
          break;
        case CaseFolding.ToLower:
          name = name.ToLowerInvariant();
          break;
      }
      return name;
    }

    private static bool VerifyName(string name)
    {
      try
      {
        XmlConvert.VerifyName(name);
        return true;
      }
      catch (XmlException)
      {
        return false;
      }
    }

    private const string tagterm = " \t\r\n=/><";
    private const string aterm = " \t\r\n='\"/>";
    private const string avterm = " \t\r\n>";
    private bool ParseStartTag(char ch)
    {
      string name = null;
      if (m_state != State.PseudoStartTag)
      {
        if (SgmlReader.tagterm.IndexOf(ch) >= 0)
        {
          this.m_sb.Length = 0;
          this.m_sb.Append('<');
          this.m_state = State.PartialText;
          return false;
        }

        name = ScanName(SgmlReader.tagterm);
      }
      else
      {
        // TODO: Changes by mindtouch mean that  this.startTag is never non-null.  The effects of this need checking.

        //name = this.startTag;
        m_state = State.Markup;
      }

      Node n = Push(name, XmlNodeType.Element, null);
      n.IsEmpty = false;
      Validate(n);
      ch = this.m_current.SkipWhitespace();
      while (ch != Entity.EOF && ch != '>')
      {
        if (ch == '/')
        {
          n.IsEmpty = true;
          ch = this.m_current.ReadChar();
          if (ch != '>')
          {
            Log("Expected empty start tag '/>' sequence instead of '{0}'", ch);
            this.m_current.ScanToEnd(null, "Recovering", ">");
            return false;
          }
          break;
        }
        else if (ch == '<')
        {
          Log("Start tag '{0}' is missing '>'", name);
          break;
        }

        string aname = ScanName(SgmlReader.aterm);
        ch = this.m_current.SkipWhitespace();
        if (string.Equals(aname, ",", StringComparison.OrdinalIgnoreCase) ||
            string.Equals(aname, "=", StringComparison.OrdinalIgnoreCase) ||
            string.Equals(aname, ":", StringComparison.OrdinalIgnoreCase) ||
            string.Equals(aname, ";", StringComparison.OrdinalIgnoreCase))
        {
          continue;
        }

        string value = null;
        char quote = '\0';
        if (ch == '=' || ch == '"' || ch == '\'')
        {
          if (ch == '=')
          {
            this.m_current.ReadChar();
            ch = this.m_current.SkipWhitespace();
          }

          if (ch == '\'' || ch == '\"')
          {
            quote = ch;
            value = ScanLiteral(this.m_sb, ch);
          }
          else if (ch != '>')
          {
            string term = SgmlReader.avterm;
            value = this.m_current.ScanToken(this.m_sb, term, false);
          }
        }

        if (ValidAttributeName(aname))
        {
          Attribute a = n.AddAttribute(aname, value ?? aname, quote, this.m_folding == CaseFolding.None);
          if (a == null)
          {
            Log("Duplicate attribute '{0}' ignored", aname);
          }
          else
          {
            ValidateAttribute(n, a);
          }
        }

        ch = this.m_current.SkipWhitespace();
      }

      if (ch == Entity.EOF)
      {
        this.m_current.Error("Unexpected EOF parsing start tag '{0}'", name);
      }
      else if (ch == '>')
      {
        this.m_current.ReadChar(); // consume '>'
      }

      if (this.Depth == 1)
      {
        if (this.m_rootCount == 1)
        {
          // Hmmm, we found another root level tag, soooo, the only
          // thing we can do to keep this a valid XML document is stop
          this.m_state = State.Eof;
          return false;
        }
        this.m_rootCount++;
      }

      ValidateContent(n);
      return true;
    }

    private bool ParseEndTag()
    {
      this.m_state = State.EndTag;
      this.m_current.ReadChar(); // consume '/' char.
      string name = this.ScanName(SgmlReader.tagterm);
      char ch = this.m_current.SkipWhitespace();
      if (ch != '>')
      {
        Log("Expected empty start tag '/>' sequence instead of '{0}'", ch);
        this.m_current.ScanToEnd(null, "Recovering", ">");
      }

      this.m_current.ReadChar(); // consume '>'

      this.m_endTag = name;

      // Make sure there's a matching start tag for it.                        
      bool caseInsensitive = (this.m_folding == CaseFolding.None);
      this.m_node = (Node)this.m_stack[this.m_stack.Count - 1];
      for (int i = this.m_stack.Count - 1; i > 0; i--)
      {
        Node n = (Node)this.m_stack[i];
        if (string.Equals(n.Name, name, caseInsensitive ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal))
        {
          this.m_endTag = n.Name;
          return true;
        }
      }

      Log("No matching start tag for '</{0}>'", name);
      this.m_state = State.Markup;
      return false;
    }

    private bool ParseAspNet()
    {
      string value = "<%" + this.m_current.ScanToEnd(this.m_sb, "AspNet", "%>") + "%>";
      Push(null, XmlNodeType.CDATA, value);
      return true;
    }

    private bool ParseComment()
    {
      char ch = this.m_current.ReadChar();
      if (ch != '-')
      {
        Log("Expecting comment '<!--' but found {0}", ch);
        this.m_current.ScanToEnd(null, "Comment", ">");
        return false;
      }

      string value = this.m_current.ScanToEnd(this.m_sb, "Comment", "-->");

      // Make sure it's a valid comment!
      int i = value.IndexOf("--");

      while (i >= 0)
      {
        int j = i + 2;
        while (j < value.Length && value[j] == '-')
          j++;

        if (i > 0)
        {
          value = value.Substring(0, i - 1) + "-" + value.Substring(j);
        }
        else
        {
          value = "-" + value.Substring(j);
        }

        i = value.IndexOf("--");
      }

      if (value.Length > 0 && value[value.Length - 1] == '-')
      {
        value += " "; // '-' cannot be last character
      }

      Push(null, XmlNodeType.Comment, value);
      return true;
    }

    private const string cdataterm = "\t\r\n[]<>";
    private bool ParseConditionalBlock()
    {
      char ch = m_current.ReadChar(); // skip '['
      ch = m_current.SkipWhitespace();
      string name = m_current.ScanToken(m_sb, cdataterm, false);
      if (name.StartsWith("if "))
      {
        // 'downlevel-revealed' comment (another atrocity of the IE team)
        m_current.ScanToEnd(null, "CDATA", ">");
        return false;
      }
      else if (!string.Equals(name, "CDATA", StringComparison.OrdinalIgnoreCase))
      {
        Log("Expecting CDATA but found '{0}'", name);
        m_current.ScanToEnd(null, "CDATA", ">");
        return false;
      }
      else
      {
        ch = m_current.SkipWhitespace();
        if (ch != '[')
        {
          Log("Expecting '[' but found '{0}'", ch);
          m_current.ScanToEnd(null, "CDATA", ">");
          return false;
        }

        string value = m_current.ScanToEnd(m_sb, "CDATA", "]]>");

        Push(null, XmlNodeType.CDATA, value);
        return true;
      }
    }

    private const string dtterm = " \t\r\n>";
    private void ParseDocType()
    {
      char ch = this.m_current.SkipWhitespace();
      string name = this.ScanName(SgmlReader.dtterm);
      Push(name, XmlNodeType.DocumentType, null);
      ch = this.m_current.SkipWhitespace();
      if (ch != '>')
      {
        string subset = "";
        string pubid = "";
        string syslit = "";

        if (ch != '[')
        {
          string token = this.m_current.ScanToken(this.m_sb, SgmlReader.dtterm, false);
          if (string.Equals(token, "PUBLIC", StringComparison.OrdinalIgnoreCase))
          {
            ch = this.m_current.SkipWhitespace();
            if (ch == '\"' || ch == '\'')
            {
              pubid = this.m_current.ScanLiteral(this.m_sb, ch);
              this.m_node.AddAttribute(token, pubid, ch, this.m_folding == CaseFolding.None);
            }
          }
          else if (!string.Equals(token, "SYSTEM", StringComparison.OrdinalIgnoreCase))
          {
            Log("Unexpected token in DOCTYPE '{0}'", token);
            this.m_current.ScanToEnd(null, "DOCTYPE", ">");
          }
          ch = this.m_current.SkipWhitespace();
          if (ch == '\"' || ch == '\'')
          {
            token = "SYSTEM";
            syslit = this.m_current.ScanLiteral(this.m_sb, ch);
            this.m_node.AddAttribute(token, syslit, ch, this.m_folding == CaseFolding.None);
          }
          ch = this.m_current.SkipWhitespace();
        }

        if (ch == '[')
        {
          subset = this.m_current.ScanToEnd(this.m_sb, "Internal Subset", "]");
          this.m_node.Value = subset;
        }

        ch = this.m_current.SkipWhitespace();
        if (ch != '>')
        {
          Log("Expecting end of DOCTYPE tag, but found '{0}'", ch);
          this.m_current.ScanToEnd(null, "DOCTYPE", ">");
        }

        if (this.m_dtd != null && !string.Equals(this.m_dtd.Name, name, StringComparison.OrdinalIgnoreCase))
        {
          throw new InvalidOperationException("DTD does not match document type");
        }

        this.m_docType = name;
        this.m_pubid = pubid;
        this.m_syslit = syslit;
        this.m_subset = subset;
        LazyLoadDtd(this.m_current.ResolvedUri);
      }

      this.m_current.ReadChar();
    }

    private const string piterm = " \t\r\n?";
    private bool ParsePI()
    {
      string name = this.m_current.ScanToken(this.m_sb, SgmlReader.piterm, false);
      string value = null;
      if (this.m_current.Lastchar != '?')
      {
        // Notice this is not "?>".  This is because Office generates bogus PI's that end with "/>".
        value = this.m_current.ScanToEnd(this.m_sb, "Processing Instruction", ">");
        value = value.TrimEnd('/');
      }
      else
      {
        // error recovery.
        value = this.m_current.ScanToEnd(this.m_sb, "Processing Instruction", ">");
      }

      // check if the name has a prefix; if so, ignore it
      int colon = name.IndexOf(':');
      if (colon > 0)
      {
        name = name.Substring(colon + 1);
      }

      // skip xml declarations, since these are generated in the output instead.
      if (!string.Equals(name, "xml", StringComparison.OrdinalIgnoreCase))
      {
        Push(name, XmlNodeType.ProcessingInstruction, value);
        return true;
      }

      return false;
    }

    private bool ParseText(char ch, bool newtext)
    {
      bool ws = !newtext || this.m_current.IsWhitespace;
      if (newtext)
        this.m_sb.Length = 0;

      //this.sb.Append(ch);
      //ch = this.current.ReadChar();
      this.m_state = State.Text;
      while (ch != Entity.EOF)
      {
        if (ch == '<')
        {
          ch = this.m_current.ReadChar();
          if (ch == '/' || ch == '!' || ch == '?' || char.IsLetter(ch))
          {
            // Hit a tag, so return XmlNodeType.Text token
            // and remember we partially started a new tag.
            this.m_state = State.PartialTag;
            this.m_partial = ch;
            break;
          }
          else
          {
            // not a tag, so just proceed.
            this.m_sb.Append('<');
            this.m_sb.Append(ch);
            ws = false;
            ch = this.m_current.ReadChar();
          }
        }
        else if (ch == '&')
        {
          ExpandEntity(this.m_sb, '<');
          ws = false;
          ch = this.m_current.Lastchar;
        }
        else
        {
          if (!this.m_current.IsWhitespace)
            ws = false;
          this.m_sb.Append(ch);
          ch = this.m_current.ReadChar();
        }
      }

      string value = this.m_sb.ToString();
      Push(null, XmlNodeType.Text, value);
      return ws;
    }

    /// <summary>
    /// Consumes and returns a literal block of text, expanding entities as it does so.
    /// </summary>
    /// <param name="sb">The string builder to use.</param>
    /// <param name="quote">The delimiter for the literal.</param>
    /// <returns>The consumed literal.</returns>
    /// <remarks>
    /// This version is slightly different from <see cref="Entity.ScanLiteral"/> in that
    /// it also expands entities.
    /// </remarks>
    private string ScanLiteral(StringBuilder sb, char quote)
    {
      sb.Length = 0;
      char ch = this.m_current.ReadChar();
      while (ch != Entity.EOF && ch != quote && ch != '>')
      {
        if (ch == '&')
        {
          ExpandEntity(sb, quote);
          ch = this.m_current.Lastchar;
        }
        else
        {
          sb.Append(ch);
          ch = this.m_current.ReadChar();
        }
      }
      if (ch == quote)
      {
        this.m_current.ReadChar(); // consume end quote.
      }
      return sb.ToString();
    }

    private bool ParseCData()
    {
      // Like ParseText(), only it doesn't allow elements in the content.  
      // It allows comments and processing instructions and text only and
      // text is not returned as text but CDATA (since it may contain angle brackets).
      // And initial whitespace is ignored.  It terminates when we hit the
      // end tag for the current CDATA node (e.g. </style>).
      bool ws = this.m_current.IsWhitespace;
      this.m_sb.Length = 0;
      char ch = this.m_current.Lastchar;
      if (this.m_partial != '\0')
      {
        Pop(); // pop the CDATA
        switch (this.m_partial)
        {
          case '!':
            this.m_partial = ' '; // and pop the comment next time around
            return ParseComment();
          case '?':
            this.m_partial = ' '; // and pop the PI next time around
            return ParsePI();
          case '/':
            this.m_state = State.EndTag;
            return true;    // we are done!
          case ' ':
            break; // means we just needed to pop the Comment, PI or CDATA.
        }
      }

      // if this.partial == '!' then parse the comment and return
      // if this.partial == '?' then parse the processing instruction and return.            
      while (ch != Entity.EOF)
      {
        if (ch == '<')
        {
          ch = this.m_current.ReadChar();
          if (ch == '!')
          {
            ch = this.m_current.ReadChar();
            if (ch == '-')
            {
              // return what CDATA we have accumulated so far
              // then parse the comment and return to here.
              if (ws)
              {
                this.m_partial = ' '; // pop comment next time through
                return ParseComment();
              }
              else
              {
                // return what we've accumulated so far then come
                // back in and parse the comment.
                this.m_partial = '!';
                break;
              }
#if FIX
                        } else if (ch == '['){
                            // We are about to wrap this node as a CDATA block because of it's
                            // type in the DTD, but since we found a CDATA block in the input
                            // we have to parse it as a CDATA block, otherwise we will attempt
                            // to output nested CDATA blocks which of course is illegal.
                            if (this.ParseConditionalBlock()){
                                this.partial = ' ';
                                return true;
                            }
#endif
            }
            else
            {
              // not a comment, so ignore it and continue on.
              this.m_sb.Append('<');
              this.m_sb.Append('!');
              this.m_sb.Append(ch);
              ws = false;
            }
          }
          else if (ch == '?')
          {
            // processing instruction.
            this.m_current.ReadChar();// consume the '?' character.
            if (ws)
            {
              this.m_partial = ' '; // pop PI next time through
              return ParsePI();
            }
            else
            {
              this.m_partial = '?';
              break;
            }
          }
          else if (ch == '/')
          {
            // see if this is the end tag for this CDATA node.
            string temp = this.m_sb.ToString();
            if (ParseEndTag() && string.Equals(this.m_endTag, this.m_node.Name, StringComparison.OrdinalIgnoreCase))
            {
              if (ws || string.IsNullOrEmpty(temp))
              {
                // we are done!
                return true;
              }
              else
              {
                // return CDATA text then the end tag
                this.m_partial = '/';
                this.m_sb.Length = 0; // restore buffer!
                this.m_sb.Append(temp);
                this.m_state = State.CData;
                break;
              }
            }
            else
            {
              // wrong end tag, so continue on.
              this.m_sb.Length = 0; // restore buffer!
              this.m_sb.Append(temp);
              this.m_sb.Append("</" + this.m_endTag + ">");
              ws = false;

              // NOTE (steveb): we have one character in the buffer that we need to process next
              ch = this.m_current.Lastchar;
              continue;
            }
          }
          else
          {
            // must be just part of the CDATA block, so proceed.
            this.m_sb.Append('<');
            this.m_sb.Append(ch);
            ws = false;
          }
        }
        else
        {
          if (!this.m_current.IsWhitespace && ws)
            ws = false;
          this.m_sb.Append(ch);
        }

        ch = this.m_current.ReadChar();
      }

      // NOTE (steveb): check if we reached EOF, which means it's over
      if (ch == Entity.EOF)
      {
        this.m_state = State.Eof;
        return false;
      }

      string value = this.m_sb.ToString();

      // NOTE (steveb): replace any nested CDATA sections endings
      value = value.Replace("<![CDATA[", string.Empty);
      value = value.Replace("]]>", string.Empty);
      value = value.Replace("/**/", string.Empty);

      Push(null, XmlNodeType.CDATA, value);
      if (this.m_partial == '\0')
        this.m_partial = ' ';// force it to pop this CDATA next time in.

      return true;
    }

    private void ExpandEntity(StringBuilder sb, char terminator)
    {
      char ch = this.m_current.ReadChar();
      if (ch == '#')
      {
        string charent = this.m_current.ExpandCharEntity();
        sb.Append(charent);
        ch = this.m_current.Lastchar;
      }
      else
      {
        this.m_name.Length = 0;
        while (ch != Entity.EOF &&
            (char.IsLetter(ch) || ch == '_' || ch == '-') || ((this.m_name.Length > 0) && char.IsDigit(ch)))
        {
          this.m_name.Append(ch);
          ch = this.m_current.ReadChar();
        }
        string name = this.m_name.ToString();

        // TODO (steveb): don't lookup amp, gt, lt, quote
        switch (name)
        {
          case "amp":
            sb.Append("&");
            if (ch != terminator && ch != '&' && ch != Entity.EOF)
              ch = this.m_current.ReadChar();
            return;
          case "lt":
            sb.Append("<");
            if (ch != terminator && ch != '&' && ch != Entity.EOF)
              ch = this.m_current.ReadChar();
            return;
          case "gt":
            sb.Append(">");
            if (ch != terminator && ch != '&' && ch != Entity.EOF)
              ch = this.m_current.ReadChar();
            return;
          case "quot":
            sb.Append("\"");
            if (ch != terminator && ch != '&' && ch != Entity.EOF)
              ch = this.m_current.ReadChar();
            return;
          case "apos":
            sb.Append("'");
            if (ch != terminator && ch != '&' && ch != Entity.EOF)
              ch = this.m_current.ReadChar();
            return;
        }

        if (this.m_dtd != null && !string.IsNullOrEmpty(name))
        {
          Entity e = (Entity)this.m_dtd.FindEntity(name);
          if (e != null)
          {
            if (e.IsInternal)
            {
              sb.Append(e.Literal);
              if (ch != terminator && ch != '&' && ch != Entity.EOF)
                ch = this.m_current.ReadChar();

              return;
            }
            else
            {
              Entity ex = new Entity(name, e.PublicId, e.Uri, this.m_current.Proxy);
              e.Open(this.m_current, new Uri(e.Uri));
              this.m_current = ex;
              this.m_current.ReadChar();
              return;
            }
          }
          else
          {
            Log("Undefined entity '{0}'", name);
          }
        }
        // Entity is not defined, so just keep it in with the rest of the
        // text.
        sb.Append("&");
        sb.Append(name);
        if (ch != terminator && ch != '&' && ch != Entity.EOF)
        {
          sb.Append(ch);
          ch = this.m_current.ReadChar();
        }
      }
    }

    /// <summary>
    /// Gets a value indicating whether the reader is positioned at the end of the stream.
    /// </summary>
    /// <value>true if the reader is positioned at the end of the stream; otherwise, false.</value>
    public override bool EOF
    {
      get
      {
        return this.m_state == State.Eof;
      }
    }

#if !PORTABLE
        public override void Close()
        {
            ((IDisposable)this).Dispose();
        }
#endif

    /// <summary>
    /// Changes the <see cref="ReadState"/> to Closed.
    /// </summary>
    protected override void Dispose(bool disposing)
    {
      base.Dispose(disposing);
      if (!disposing)
      {
        return;
      }

      if (this.m_current != null)
      {
        this.m_current.Close();
        this.m_current = null;
      }

      if (this.m_log != null)
      {
        this.m_log.Dispose();
        this.m_log = null;
      }
    }

    /// <summary>
    /// Gets the state of the reader.
    /// </summary>
    /// <value>One of the ReadState values.</value>
    public override ReadState ReadState
    {
      get
      {
        if (this.m_state == State.Initial)
          return ReadState.Initial;
        else if (this.m_state == State.Eof)
          return ReadState.EndOfFile;
        else
          return ReadState.Interactive;
      }
    }

    /// <summary>
    /// Reads the contents of an element or text node as a string.
    /// </summary>
    /// <returns>The contents of the element or an empty string.</returns>
#if PORTABLE
    public override string ReadContentAsString()
#else
        public override string ReadString()
#endif
    {
      if (this.m_node.NodeType == XmlNodeType.Element)
      {
        this.m_sb.Length = 0;
        while (Read())
        {
          switch (this.NodeType)
          {
            case XmlNodeType.CDATA:
            case XmlNodeType.SignificantWhitespace:
            case XmlNodeType.Whitespace:
            case XmlNodeType.Text:
              this.m_sb.Append(this.m_node.Value);
              break;
            default:
              return this.m_sb.ToString();
          }
        }

        return this.m_sb.ToString();
      }

      return this.m_node.Value;
    }

    /// <summary>
    /// Reads all the content, including markup, as a string.
    /// </summary>
    /// <returns>
    /// All the XML content, including markup, in the current node. If the current node has no children,
    /// an empty string is returned. If the current node is neither an element nor attribute, an empty
    /// string is returned.
    /// </returns>
    public override string ReadInnerXml()
    {
      StringWriter sw = new StringWriter(CultureInfo.InvariantCulture);
      XmlWriter xw = XmlWriter.Create(sw, new XmlWriterSettings { Indent = true, IndentChars = "  " });
      switch (this.NodeType)
      {
        case XmlNodeType.Element:
          Read();
          while (!this.EOF && this.NodeType != XmlNodeType.EndElement)
          {
            xw.WriteNode(this, true);
          }
          Read(); // consume the end tag
          break;
        case XmlNodeType.Attribute:
          sw.Write(this.Value);
          break;
        default:
          // return empty string according to XmlReader spec.
          break;
      }

#if PORTABLE
      xw.Dispose();
#else
            xw.Close();
#endif
      return sw.ToString();
    }

    /// <summary>
    /// Reads the content, including markup, representing this node and all its children.
    /// </summary>
    /// <returns>
    /// If the reader is positioned on an element or an attribute node, this method returns all the XML content, including markup, of the current node and all its children; otherwise, it returns an empty string.
    /// </returns>
    public override string ReadOuterXml()
    {
      StringWriter sw = new StringWriter(CultureInfo.InvariantCulture);
      XmlWriter xw = XmlWriter.Create(sw, new XmlWriterSettings { Indent = true, IndentChars = "  " });
      xw.WriteNode(this, true);
#if PORTABLE
      xw.Dispose();
#else
            xw.Close();
#endif
      return sw.ToString();
    }

    /// <summary>
    /// Gets the XmlNameTable associated with this implementation.
    /// </summary>
    /// <value>The XmlNameTable enabling you to get the atomized version of a string within the node.</value>
    public override XmlNameTable NameTable
    {
      get
      {
        return null;
      }
    }

    /// <summary>
    /// Resolves a namespace prefix in the current element's scope.
    /// </summary>
    /// <param name="prefix">The prefix whose namespace URI you want to resolve. To match the default namespace, pass an empty string.</param>
    /// <returns>The namespace URI to which the prefix maps or a null reference (Nothing in Visual Basic) if no matching prefix is found.</returns>
    public override string LookupNamespace(string prefix)
    {
      return null; // there are no namespaces in SGML.
    }

    /// <summary>
    /// Resolves the entity reference for EntityReference nodes.
    /// </summary>
    /// <exception cref="InvalidOperationException">SgmlReader does not resolve or return entities.</exception>
    public override void ResolveEntity()
    {
      // We never return any entity reference nodes, so this should never be called.
      throw new InvalidOperationException("Not on an entity reference.");
    }

    /// <summary>
    /// Parses the attribute value into one or more Text, EntityReference, or EndEntity nodes.
    /// </summary>
    /// <returns>
    /// true if there are nodes to return. false if the reader is not positioned on an attribute node when the initial call is made or if all the
    /// attribute values have been read. An empty attribute, such as, misc="", returns true with a single node with a value of string.Empty.
    /// </returns>
    public override bool ReadAttributeValue()
    {
      if (this.m_state == State.Attr)
      {
        this.m_state = State.AttrValue;
        return true;
      }
      else if (this.m_state == State.AttrValue)
      {
        return false;
      }
      else
        throw new InvalidOperationException("Not on an attribute.");
    }

    private void Validate(Node node)
    {
      if (this.m_dtd != null)
      {
        ElementDecl e = this.m_dtd.FindElement(node.Name);
        if (e != null)
        {
          node.DtdType = e;
          if (e.ContentModel.DeclaredContent == DeclaredContent.EMPTY)
            node.IsEmpty = true;
        }
      }
    }

    private static void ValidateAttribute(Node node, Attribute a)
    {
      ElementDecl e = node.DtdType;
      if (e != null)
      {
        AttDef ad = e.FindAttribute(a.Name);
        if (ad != null)
        {
          a.DtdType = ad;
        }
      }
    }

    private static bool ValidAttributeName(string name)
    {
      try
      {
        XmlConvert.VerifyNMTOKEN(name);
        int index = name.IndexOf(':');
        if (index >= 0)
        {
          XmlConvert.VerifyNCName(name.Substring(index + 1));
        }

        return true;
      }
      catch (XmlException)
      {
        return false;
      }
      catch (ArgumentNullException)
      {
        // (steveb) this is probably a bug in XmlConvert.VerifyNCName when passing in an empty string
        return false;
      }
    }

    private void ValidateContent(Node node)
    {
      if (node.NodeType == XmlNodeType.Element)
      {
        if (!VerifyName(node.Name))
        {
          Pop();
          Push(null, XmlNodeType.Text, "<" + node.Name + ">");
          return;
        }
      }

      if (this.m_dtd != null)
      {
        // See if this element is allowed inside the current element.
        // If it isn't, then auto-close elements until we find one
        // that it is allowed to be in.                                  
        string name = node.Name.ToUpperInvariant(); // DTD is in upper case
        int i = 0;
        int top = this.m_stack.Count - 2;
        if (node.DtdType != null)
        {
          // it is a known element, let's see if it's allowed in the
          // current context.
          for (i = top; i > 0; i--)
          {
            Node n = (Node)this.m_stack[i];
            if (n.IsEmpty)
              continue; // we'll have to pop this one
            ElementDecl f = n.DtdType;
            if (f != null)
            {
              if ((i == 2) && string.Equals(f.Name, "BODY", StringComparison.OrdinalIgnoreCase)) // NOTE (steveb): never close the BODY tag too early
                break;
              else if (string.Equals(f.Name, this.m_dtd.Name, StringComparison.OrdinalIgnoreCase))
                break; // can't pop the root element.
              else if (f.CanContain(name, this.m_dtd))
              {
                break;
              }
              else if (!f.EndTagOptional)
              {
                // If the end tag is not optional then we can't
                // auto-close it.  We'll just have to live with the
                // junk we've found and move on.
                break;
              }
            }
            else
            {
              // Since we don't understand this tag anyway,
              // we might as well allow this content!
              break;
            }
          }
        }

        if (i == 0)
        {
          // Tag was not found or is not allowed anywhere, ignore it and 
          // continue on.
          return;
        }
        else if (i < top)
        {
          Node n = (Node)this.m_stack[top];
          if (i == top - 1 && string.Equals(name, n.Name, StringComparison.OrdinalIgnoreCase))
          {
            // e.g. p not allowed inside p, not an interesting error.
          }
          else
          {
#if DEBUG
            string closing = "";
            for (int k = top; k >= i + 1; k--)
            {
              if (closing != "") closing += ",";
              Node n2 = (Node)this.m_stack[k];
              closing += "<" + n2.Name + ">";
            }
            Log("Element '{0}' not allowed inside '{1}', closing {2}.", name, n.Name, closing);
#endif
          }

          this.m_state = State.AutoClose;
          this.m_newnode = node;
          Pop(); // save this new node until we pop the others
          this.m_poptodepth = i + 1;
        }
      }
    }
  }
}