//
// HttpUtility.cs
//	Copied from System.Net.HttpUtility.cs
//
// Authors:
//	Patrik Torstensson (Patrik.Torstensson@labs2.com)
//	Wictor Wilén (decode/encode functions) (wictor@ibizkit.se)
//	Tim Coleman (tim@timcoleman.com)
//	Gonzalo Paniagua Javier (gonzalo@ximian.com)
//
// Copyright (C) 2005-2009 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Globalization;
using System.IO;
using System.Net;
using System.Security.Permissions;
using System.Text;

namespace WebSocketSharp.Net {

	internal sealed class HttpUtility {

		sealed class HttpQSCollection : NameValueCollection
		{
			public override string ToString ()
			{
				int count = Count;
				if (count == 0)
					return "";

				StringBuilder sb = new StringBuilder ();
				string [] keys = AllKeys;
				for (int i = 0; i < count; i++) {
					sb.AppendFormat ("{0}={1}&", keys [i], this [keys [i]]);
				}

				if (sb.Length > 0)
					sb.Length--;

				return sb.ToString ();
			}
		}

		#region Fields

		static Hashtable entities;
		static char []   hexChars = "0123456789abcdef".ToCharArray ();
		static object    lock_ = new object ();

		#endregion // Fields

		#region Constructor

		public HttpUtility () 
		{
		}

		#endregion // Constructor

		#region Property

		static Hashtable Entities {
			get {
				lock (lock_) {
					if (entities == null)
						InitEntities ();

					return entities;
				}
			}
		}

		#endregion // Property

		#region Private Methods

		static int GetChar (byte [] bytes, int offset, int length)
		{
			int value = 0;
			int end = length + offset;
			for (int i = offset; i < end; i++) {
				int current = GetInt (bytes [i]);
				if (current == -1)
					return -1;

				value = (value << 4) + current;
			}

			return value;
		}

		static int GetChar (string str, int offset, int length)
		{
			int val = 0;
			int end = length + offset;
			for (int i = offset; i < end; i++) {
				char c = str [i];
				if (c > 127)
					return -1;

				int current = GetInt ((byte) c);
				if (current == -1)
					return -1;

				val = (val << 4) + current;
			}

			return val;
		}

		static char [] GetChars (MemoryStream b, Encoding e)
		{
			return e.GetChars (b.GetBuffer (), 0, (int) b.Length);
		}

		static int GetInt (byte b)
		{
			char c = (char) b;
			if (c >= '0' && c <= '9')
				return c - '0';

			if (c >= 'a' && c <= 'f')
				return c - 'a' + 10;

			if (c >= 'A' && c <= 'F')
				return c - 'A' + 10;

			return -1;
		}

		static void InitEntities ()
		{
			// Build the hash table of HTML entity references. This list comes
			// from the HTML 4.01 W3C recommendation.
			entities = new Hashtable ();
			entities.Add ("nbsp", '\u00A0');
			entities.Add ("iexcl", '\u00A1');
			entities.Add ("cent", '\u00A2');
			entities.Add ("pound", '\u00A3');
			entities.Add ("curren", '\u00A4');
			entities.Add ("yen", '\u00A5');
			entities.Add ("brvbar", '\u00A6');
			entities.Add ("sect", '\u00A7');
			entities.Add ("uml", '\u00A8');
			entities.Add ("copy", '\u00A9');
			entities.Add ("ordf", '\u00AA');
			entities.Add ("laquo", '\u00AB');
			entities.Add ("not", '\u00AC');
			entities.Add ("shy", '\u00AD');
			entities.Add ("reg", '\u00AE');
			entities.Add ("macr", '\u00AF');
			entities.Add ("deg", '\u00B0');
			entities.Add ("plusmn", '\u00B1');
			entities.Add ("sup2", '\u00B2');
			entities.Add ("sup3", '\u00B3');
			entities.Add ("acute", '\u00B4');
			entities.Add ("micro", '\u00B5');
			entities.Add ("para", '\u00B6');
			entities.Add ("middot", '\u00B7');
			entities.Add ("cedil", '\u00B8');
			entities.Add ("sup1", '\u00B9');
			entities.Add ("ordm", '\u00BA');
			entities.Add ("raquo", '\u00BB');
			entities.Add ("frac14", '\u00BC');
			entities.Add ("frac12", '\u00BD');
			entities.Add ("frac34", '\u00BE');
			entities.Add ("iquest", '\u00BF');
			entities.Add ("Agrave", '\u00C0');
			entities.Add ("Aacute", '\u00C1');
			entities.Add ("Acirc", '\u00C2');
			entities.Add ("Atilde", '\u00C3');
			entities.Add ("Auml", '\u00C4');
			entities.Add ("Aring", '\u00C5');
			entities.Add ("AElig", '\u00C6');
			entities.Add ("Ccedil", '\u00C7');
			entities.Add ("Egrave", '\u00C8');
			entities.Add ("Eacute", '\u00C9');
			entities.Add ("Ecirc", '\u00CA');
			entities.Add ("Euml", '\u00CB');
			entities.Add ("Igrave", '\u00CC');
			entities.Add ("Iacute", '\u00CD');
			entities.Add ("Icirc", '\u00CE');
			entities.Add ("Iuml", '\u00CF');
			entities.Add ("ETH", '\u00D0');
			entities.Add ("Ntilde", '\u00D1');
			entities.Add ("Ograve", '\u00D2');
			entities.Add ("Oacute", '\u00D3');
			entities.Add ("Ocirc", '\u00D4');
			entities.Add ("Otilde", '\u00D5');
			entities.Add ("Ouml", '\u00D6');
			entities.Add ("times", '\u00D7');
			entities.Add ("Oslash", '\u00D8');
			entities.Add ("Ugrave", '\u00D9');
			entities.Add ("Uacute", '\u00DA');
			entities.Add ("Ucirc", '\u00DB');
			entities.Add ("Uuml", '\u00DC');
			entities.Add ("Yacute", '\u00DD');
			entities.Add ("THORN", '\u00DE');
			entities.Add ("szlig", '\u00DF');
			entities.Add ("agrave", '\u00E0');
			entities.Add ("aacute", '\u00E1');
			entities.Add ("acirc", '\u00E2');
			entities.Add ("atilde", '\u00E3');
			entities.Add ("auml", '\u00E4');
			entities.Add ("aring", '\u00E5');
			entities.Add ("aelig", '\u00E6');
			entities.Add ("ccedil", '\u00E7');
			entities.Add ("egrave", '\u00E8');
			entities.Add ("eacute", '\u00E9');
			entities.Add ("ecirc", '\u00EA');
			entities.Add ("euml", '\u00EB');
			entities.Add ("igrave", '\u00EC');
			entities.Add ("iacute", '\u00ED');
			entities.Add ("icirc", '\u00EE');
			entities.Add ("iuml", '\u00EF');
			entities.Add ("eth", '\u00F0');
			entities.Add ("ntilde", '\u00F1');
			entities.Add ("ograve", '\u00F2');
			entities.Add ("oacute", '\u00F3');
			entities.Add ("ocirc", '\u00F4');
			entities.Add ("otilde", '\u00F5');
			entities.Add ("ouml", '\u00F6');
			entities.Add ("divide", '\u00F7');
			entities.Add ("oslash", '\u00F8');
			entities.Add ("ugrave", '\u00F9');
			entities.Add ("uacute", '\u00FA');
			entities.Add ("ucirc", '\u00FB');
			entities.Add ("uuml", '\u00FC');
			entities.Add ("yacute", '\u00FD');
			entities.Add ("thorn", '\u00FE');
			entities.Add ("yuml", '\u00FF');
			entities.Add ("fnof", '\u0192');
			entities.Add ("Alpha", '\u0391');
			entities.Add ("Beta", '\u0392');
			entities.Add ("Gamma", '\u0393');
			entities.Add ("Delta", '\u0394');
			entities.Add ("Epsilon", '\u0395');
			entities.Add ("Zeta", '\u0396');
			entities.Add ("Eta", '\u0397');
			entities.Add ("Theta", '\u0398');
			entities.Add ("Iota", '\u0399');
			entities.Add ("Kappa", '\u039A');
			entities.Add ("Lambda", '\u039B');
			entities.Add ("Mu", '\u039C');
			entities.Add ("Nu", '\u039D');
			entities.Add ("Xi", '\u039E');
			entities.Add ("Omicron", '\u039F');
			entities.Add ("Pi", '\u03A0');
			entities.Add ("Rho", '\u03A1');
			entities.Add ("Sigma", '\u03A3');
			entities.Add ("Tau", '\u03A4');
			entities.Add ("Upsilon", '\u03A5');
			entities.Add ("Phi", '\u03A6');
			entities.Add ("Chi", '\u03A7');
			entities.Add ("Psi", '\u03A8');
			entities.Add ("Omega", '\u03A9');
			entities.Add ("alpha", '\u03B1');
			entities.Add ("beta", '\u03B2');
			entities.Add ("gamma", '\u03B3');
			entities.Add ("delta", '\u03B4');
			entities.Add ("epsilon", '\u03B5');
			entities.Add ("zeta", '\u03B6');
			entities.Add ("eta", '\u03B7');
			entities.Add ("theta", '\u03B8');
			entities.Add ("iota", '\u03B9');
			entities.Add ("kappa", '\u03BA');
			entities.Add ("lambda", '\u03BB');
			entities.Add ("mu", '\u03BC');
			entities.Add ("nu", '\u03BD');
			entities.Add ("xi", '\u03BE');
			entities.Add ("omicron", '\u03BF');
			entities.Add ("pi", '\u03C0');
			entities.Add ("rho", '\u03C1');
			entities.Add ("sigmaf", '\u03C2');
			entities.Add ("sigma", '\u03C3');
			entities.Add ("tau", '\u03C4');
			entities.Add ("upsilon", '\u03C5');
			entities.Add ("phi", '\u03C6');
			entities.Add ("chi", '\u03C7');
			entities.Add ("psi", '\u03C8');
			entities.Add ("omega", '\u03C9');
			entities.Add ("thetasym", '\u03D1');
			entities.Add ("upsih", '\u03D2');
			entities.Add ("piv", '\u03D6');
			entities.Add ("bull", '\u2022');
			entities.Add ("hellip", '\u2026');
			entities.Add ("prime", '\u2032');
			entities.Add ("Prime", '\u2033');
			entities.Add ("oline", '\u203E');
			entities.Add ("frasl", '\u2044');
			entities.Add ("weierp", '\u2118');
			entities.Add ("image", '\u2111');
			entities.Add ("real", '\u211C');
			entities.Add ("trade", '\u2122');
			entities.Add ("alefsym", '\u2135');
			entities.Add ("larr", '\u2190');
			entities.Add ("uarr", '\u2191');
			entities.Add ("rarr", '\u2192');
			entities.Add ("darr", '\u2193');
			entities.Add ("harr", '\u2194');
			entities.Add ("crarr", '\u21B5');
			entities.Add ("lArr", '\u21D0');
			entities.Add ("uArr", '\u21D1');
			entities.Add ("rArr", '\u21D2');
			entities.Add ("dArr", '\u21D3');
			entities.Add ("hArr", '\u21D4');
			entities.Add ("forall", '\u2200');
			entities.Add ("part", '\u2202');
			entities.Add ("exist", '\u2203');
			entities.Add ("empty", '\u2205');
			entities.Add ("nabla", '\u2207');
			entities.Add ("isin", '\u2208');
			entities.Add ("notin", '\u2209');
			entities.Add ("ni", '\u220B');
			entities.Add ("prod", '\u220F');
			entities.Add ("sum", '\u2211');
			entities.Add ("minus", '\u2212');
			entities.Add ("lowast", '\u2217');
			entities.Add ("radic", '\u221A');
			entities.Add ("prop", '\u221D');
			entities.Add ("infin", '\u221E');
			entities.Add ("ang", '\u2220');
			entities.Add ("and", '\u2227');
			entities.Add ("or", '\u2228');
			entities.Add ("cap", '\u2229');
			entities.Add ("cup", '\u222A');
			entities.Add ("int", '\u222B');
			entities.Add ("there4", '\u2234');
			entities.Add ("sim", '\u223C');
			entities.Add ("cong", '\u2245');
			entities.Add ("asymp", '\u2248');
			entities.Add ("ne", '\u2260');
			entities.Add ("equiv", '\u2261');
			entities.Add ("le", '\u2264');
			entities.Add ("ge", '\u2265');
			entities.Add ("sub", '\u2282');
			entities.Add ("sup", '\u2283');
			entities.Add ("nsub", '\u2284');
			entities.Add ("sube", '\u2286');
			entities.Add ("supe", '\u2287');
			entities.Add ("oplus", '\u2295');
			entities.Add ("otimes", '\u2297');
			entities.Add ("perp", '\u22A5');
			entities.Add ("sdot", '\u22C5');
			entities.Add ("lceil", '\u2308');
			entities.Add ("rceil", '\u2309');
			entities.Add ("lfloor", '\u230A');
			entities.Add ("rfloor", '\u230B');
			entities.Add ("lang", '\u2329');
			entities.Add ("rang", '\u232A');
			entities.Add ("loz", '\u25CA');
			entities.Add ("spades", '\u2660');
			entities.Add ("clubs", '\u2663');
			entities.Add ("hearts", '\u2665');
			entities.Add ("diams", '\u2666');
			entities.Add ("quot", '\u0022');
			entities.Add ("amp", '\u0026');
			entities.Add ("lt", '\u003C');
			entities.Add ("gt", '\u003E');
			entities.Add ("OElig", '\u0152');
			entities.Add ("oelig", '\u0153');
			entities.Add ("Scaron", '\u0160');
			entities.Add ("scaron", '\u0161');
			entities.Add ("Yuml", '\u0178');
			entities.Add ("circ", '\u02C6');
			entities.Add ("tilde", '\u02DC');
			entities.Add ("ensp", '\u2002');
			entities.Add ("emsp", '\u2003');
			entities.Add ("thinsp", '\u2009');
			entities.Add ("zwnj", '\u200C');
			entities.Add ("zwj", '\u200D');
			entities.Add ("lrm", '\u200E');
			entities.Add ("rlm", '\u200F');
			entities.Add ("ndash", '\u2013');
			entities.Add ("mdash", '\u2014');
			entities.Add ("lsquo", '\u2018');
			entities.Add ("rsquo", '\u2019');
			entities.Add ("sbquo", '\u201A');
			entities.Add ("ldquo", '\u201C');
			entities.Add ("rdquo", '\u201D');
			entities.Add ("bdquo", '\u201E');
			entities.Add ("dagger", '\u2020');
			entities.Add ("Dagger", '\u2021');
			entities.Add ("permil", '\u2030');
			entities.Add ("lsaquo", '\u2039');
			entities.Add ("rsaquo", '\u203A');
			entities.Add ("euro", '\u20AC');
		}

		static bool NotEncoded (char c)
		{
			return (c == '!' || c == '\'' || c == '(' || c == ')' || c == '*' || c == '-' || c == '.' || c == '_');
		}

		static void UrlEncodeChar (char c, Stream result, bool isUnicode)
		{
			if (c > 255) {
				// FIXME: what happens when there is an internal error ?
				//if (!isUnicode)
				//	throw new ArgumentOutOfRangeException ("c", c, "c must be less than 256");
				int idx;
				int i = (int) c;

				result.WriteByte ((byte)'%');
				result.WriteByte ((byte)'u');
				idx = i >> 12;
				result.WriteByte ((byte)hexChars [idx]);
				idx = (i >> 8) & 0x0F;
				result.WriteByte ((byte)hexChars [idx]);
				idx = (i >> 4) & 0x0F;
				result.WriteByte ((byte)hexChars [idx]);
				idx = i & 0x0F;
				result.WriteByte ((byte)hexChars [idx]);
				return;
			}

			if (c > ' ' && NotEncoded (c)) {
				result.WriteByte ((byte)c);
				return;
			}

			if (c==' ') {
				result.WriteByte ((byte)'+');
				return;
			}

			if ((c < '0') ||
				(c < 'A' && c > '9') ||
				(c > 'Z' && c < 'a') ||
				(c > 'z')) {
				if (isUnicode && c > 127) {
					result.WriteByte ((byte)'%');
					result.WriteByte ((byte)'u');
					result.WriteByte ((byte)'0');
					result.WriteByte ((byte)'0');
				}
				else
					result.WriteByte ((byte)'%');
				
				int idx = ((int) c) >> 4;
				result.WriteByte ((byte)hexChars [idx]);
				idx = ((int) c) & 0x0F;
				result.WriteByte ((byte)hexChars [idx]);
			}
			else
				result.WriteByte ((byte)c);
		}

		static void UrlPathEncodeChar (char c, Stream result)
		{
			if (c < 33 || c > 126) {
				byte [] bIn = Encoding.UTF8.GetBytes (c.ToString ());
				for (int i = 0; i < bIn.Length; i++) {
					result.WriteByte ((byte) '%');
					int idx = ((int) bIn [i]) >> 4;
					result.WriteByte ((byte) hexChars [idx]);
					idx = ((int) bIn [i]) & 0x0F;
					result.WriteByte ((byte) hexChars [idx]);
				}
			}
			else if (c == ' ') {
				result.WriteByte ((byte) '%');
				result.WriteByte ((byte) '2');
				result.WriteByte ((byte) '0');
			}
			else
				result.WriteByte ((byte) c);
		}

		static void WriteCharBytes (IList buf, char ch, Encoding e)
		{
			if (ch > 255) {
				foreach (byte b in e.GetBytes (new char[] { ch }))
					buf.Add (b);
			} else
				buf.Add ((byte)ch);
		}

		#endregion // Private Methods

		#region Internal Method

		internal static void ParseQueryString (string query, Encoding encoding, NameValueCollection result)
		{
			if (query.Length == 0)
				return;

			string decoded = HtmlDecode (query);
			int decodedLength = decoded.Length;
			int namePos = 0;
			bool first = true;
			while (namePos <= decodedLength) {
				int valuePos = -1, valueEnd = -1;
				for (int q = namePos; q < decodedLength; q++) {
					if (valuePos == -1 && decoded [q] == '=') {
						valuePos = q + 1;
					} else if (decoded [q] == '&') {
						valueEnd = q;
						break;
					}
				}

				if (first) {
					first = false;
					if (decoded [namePos] == '?')
						namePos++;
				}

				string name, value;
				if (valuePos == -1) {
					name = null;
					valuePos = namePos;
				} else {
					name = UrlDecode (decoded.Substring (namePos, valuePos - namePos - 1), encoding);
				}

				if (valueEnd < 0) {
					namePos = -1;
					valueEnd = decoded.Length;
				} else {
					namePos = valueEnd + 1;
				}

				value = UrlDecode (decoded.Substring (valuePos, valueEnd - valuePos), encoding);
				result.Add (name, value);
				if (namePos == -1)
					break;
			}
		}

		#endregion // Internal Methods

		#region Public Methods

		public static string HtmlAttributeEncode (string s) 
		{
			if (null == s) 
				return null;
	
			bool needEncode = false;
			for (int i = 0; i < s.Length; i++) {
				if (s [i] == '&' || s [i] == '"' || s [i] == '<') {
					needEncode = true;
					break;
				}
			}

			if (!needEncode)
				return s;

			StringBuilder output = new StringBuilder ();
			int len = s.Length;
			for (int i = 0; i < len; i++)
				switch (s [i]) {
				case '&' : 
					output.Append ("&amp;");
					break;
				case '"' :
					output.Append ("&quot;");
					break;
				case '<':
					output.Append ("&lt;");
					break;
				default:
					output.Append (s [i]);
					break;
				}
	
			return output.ToString();
		}

		public static void HtmlAttributeEncode (string s, TextWriter output) 
		{
			output.Write(HtmlAttributeEncode(s));
		}

		/// <summary>
		/// Decodes an HTML-encoded string and returns the decoded string.
		/// </summary>
		/// <param name="s">The HTML string to decode.</param>
		/// <returns>The decoded text.</returns>
		public static string HtmlDecode (string s) 
		{
			if (s == null)
				throw new ArgumentNullException ("s");

			if (s.IndexOf ('&') == -1)
				return s;

			StringBuilder entity = new StringBuilder ();
			StringBuilder output = new StringBuilder ();
			int len = s.Length;
			// 0 -> nothing,
			// 1 -> right after '&'
			// 2 -> between '&' and ';' but no '#'
			// 3 -> '#' found after '&' and getting numbers
			int state = 0;
			int number = 0;
			bool have_trailing_digits = false;

			for (int i = 0; i < len; i++) {
				char c = s [i];
				if (state == 0) {
					if (c == '&') {
						entity.Append (c);
						state = 1;
					} else {
						output.Append (c);
					}
					continue;
				}

				if (c == '&') {
					state = 1;
					if (have_trailing_digits) {
						entity.Append (number.ToString (CultureInfo.InvariantCulture));
						have_trailing_digits = false;
					}

					output.Append (entity.ToString ());
					entity.Length = 0;
					entity.Append ('&');
					continue;
				}

				if (state == 1) {
					if (c == ';') {
						state = 0;
						output.Append (entity.ToString ());
						output.Append (c);
						entity.Length = 0;
					} else {
						number = 0;
						if (c != '#') {
							state = 2;
						} else {
							state = 3;
						}
						entity.Append (c);
					}
				} else if (state == 2) {
					entity.Append (c);
					if (c == ';') {
						string key = entity.ToString ();
						if (key.Length > 1 && Entities.ContainsKey (key.Substring (1, key.Length - 2)))
							key = Entities [key.Substring (1, key.Length - 2)].ToString ();

						output.Append (key);
						state = 0;
						entity.Length = 0;
					}
				} else if (state == 3) {
					if (c == ';') {
						if (number > 65535) {
							output.Append ("&#");
							output.Append (number.ToString (CultureInfo.InvariantCulture));
							output.Append (";");
						} else {
							output.Append ((char) number);
						}
						state = 0;
						entity.Length = 0;
						have_trailing_digits = false;
					} else if (Char.IsDigit (c)) {
						number = number * 10 + ((int) c - '0');
						have_trailing_digits = true;
					} else {
						state = 2;
						if (have_trailing_digits) {
							entity.Append (number.ToString (CultureInfo.InvariantCulture));
							have_trailing_digits = false;
						}
						entity.Append (c);
					}
				}
			}

			if (entity.Length > 0) {
				output.Append (entity.ToString ());
			} else if (have_trailing_digits) {
				output.Append (number.ToString (CultureInfo.InvariantCulture));
			}

			return output.ToString ();
		}

		/// <summary>
		/// Decodes an HTML-encoded string and sends the resulting output to a TextWriter output stream.
		/// </summary>
		/// <param name="s">The HTML string to decode.</param>
		/// <param name="output">The TextWriter output stream containing the decoded string.</param>
		public static void HtmlDecode (string s, TextWriter output) 
		{
			if (s != null)
				output.Write (HtmlDecode (s));
		}

		/// <summary>
		/// HTML-encodes a string and returns the encoded string.
		/// </summary>
		/// <param name="s">The text string to encode.</param>
		/// <returns>The HTML-encoded text.</returns>
		public static string HtmlEncode (string s) 
		{
			if (s == null)
				return null;

			bool needEncode = false;
			for (int i = 0; i < s.Length; i++) {
				char c = s [i];
				if (c == '&' || c == '"' || c == '<' || c == '>' || c > 159) {
					needEncode = true;
					break;
				}
			}

			if (!needEncode)
				return s;

			StringBuilder output = new StringBuilder ();

			int len = s.Length;
			for (int i = 0; i < len; i++) 
				switch (s [i]) {
				case '&' :
					output.Append ("&amp;");
					break;
				case '>' : 
					output.Append ("&gt;");
					break;
				case '<' :
					output.Append ("&lt;");
					break;
				case '"' :
					output.Append ("&quot;");
					break;
				default:
					// MS starts encoding with &# from 160 and stops at 255.
					// We don't do that. One reason is the 65308/65310 unicode
					// characters that look like '<' and '>'.
					if (s [i] > 159) {
						output.Append ("&#");
						output.Append (((int) s [i]).ToString (CultureInfo.InvariantCulture));
						output.Append (";");
					} else {
						output.Append (s [i]);
					}
					break;
				}

			return output.ToString ();
		}

		/// <summary>
		/// HTML-encodes a string and sends the resulting output to a TextWriter output stream.
		/// </summary>
		/// <param name="s">The string to encode.</param>
		/// <param name="output">The TextWriter output stream containing the encoded string.</param>
		public static void HtmlEncode (string s, TextWriter output) 
		{
			if (s != null)
				output.Write (HtmlEncode (s));
		}

		public static NameValueCollection ParseQueryString (string query)
		{
			return ParseQueryString (query, Encoding.UTF8);
		}

		public static NameValueCollection ParseQueryString (string query, Encoding encoding)
		{
			if (query == null)
				throw new ArgumentNullException ("query");

			if (encoding == null)
				throw new ArgumentNullException ("encoding");

			if (query.Length == 0 || (query.Length == 1 && query[0] == '?'))
				return new NameValueCollection ();

			if (query[0] == '?')
				query = query.Substring (1);

			NameValueCollection result = new HttpQSCollection ();
			ParseQueryString (query, encoding, result);

			return result;
		}

		public static string UrlDecode (string str) 
		{
			return UrlDecode(str, Encoding.UTF8);
		}

		public static string UrlDecode (string s, Encoding e)
		{
			if (s == null)
				return null;

			if (s.IndexOf ('%') == -1 && s.IndexOf ('+') == -1)
				return s;

			if (e == null)
				e = Encoding.UTF8;

			long len = s.Length;
			var bytes = new List <byte> ();
			int xchar;
			char ch;

			for (int i = 0; i < len; i++) {
				ch = s [i];
				if (ch == '%' && i + 2 < len && s [i + 1] != '%') {
					if (s [i + 1] == 'u' && i + 5 < len) {
						// unicode hex sequence
						xchar = GetChar (s, i + 2, 4);
						if (xchar != -1) {
							WriteCharBytes (bytes, (char)xchar, e);
							i += 5;
						} else
							WriteCharBytes (bytes, '%', e);
					} else if ((xchar = GetChar (s, i + 1, 2)) != -1) {
						WriteCharBytes (bytes, (char)xchar, e);
						i += 2;
					} else {
						WriteCharBytes (bytes, '%', e);
					}
					continue;
				}

				if (ch == '+')
					WriteCharBytes (bytes, ' ', e);
				else
					WriteCharBytes (bytes, ch, e);
			}

			byte[] buf = bytes.ToArray ();
			bytes = null;
			return e.GetString (buf);
		}

		public static string UrlDecode (byte [] bytes, Encoding e)
		{
			if (bytes == null)
				return null;

			return UrlDecode (bytes, 0, bytes.Length, e);
		}

		public static string UrlDecode (byte [] bytes, int offset, int count, Encoding e)
		{
			if (bytes == null)
				return null;
			if (count == 0)
				return String.Empty;

			if (bytes == null)
				throw new ArgumentNullException ("bytes");

			if (offset < 0 || offset > bytes.Length)
				throw new ArgumentOutOfRangeException ("offset");

			if (count < 0 || offset + count > bytes.Length)
				throw new ArgumentOutOfRangeException ("count");

			StringBuilder output = new StringBuilder ();
			MemoryStream acc = new MemoryStream ();

			int end = count + offset;
			int xchar;
			for (int i = offset; i < end; i++) {
				if (bytes [i] == '%' && i + 2 < count && bytes [i + 1] != '%') {
					if (bytes [i + 1] == (byte) 'u' && i + 5 < end) {
						if (acc.Length > 0) {
							output.Append (GetChars (acc, e));
							acc.SetLength (0);
						}
						xchar = GetChar (bytes, i + 2, 4);
						if (xchar != -1) {
							output.Append ((char) xchar);
							i += 5;
							continue;
						}
					} else if ((xchar = GetChar (bytes, i + 1, 2)) != -1) {
						acc.WriteByte ((byte) xchar);
						i += 2;
						continue;
					}
				}

				if (acc.Length > 0) {
					output.Append (GetChars (acc, e));
					acc.SetLength (0);
				}

				if (bytes [i] == '+') {
					output.Append (' ');
				} else {
					output.Append ((char) bytes [i]);
				}
			}

			if (acc.Length > 0) {
				output.Append (GetChars (acc, e));
			}
			
			acc = null;
			return output.ToString ();
		}
	
		public static byte [] UrlDecodeToBytes (byte [] bytes)
		{
			if (bytes == null)
				return null;

			return UrlDecodeToBytes (bytes, 0, bytes.Length);
		}

		public static byte [] UrlDecodeToBytes (string str)
		{
			return UrlDecodeToBytes (str, Encoding.UTF8);
		}

		public static byte [] UrlDecodeToBytes (string str, Encoding e)
		{
			if (str == null)
				return null;

			if (e == null)
				throw new ArgumentNullException ("e");

			return UrlDecodeToBytes (e.GetBytes (str));
		}

		public static byte [] UrlDecodeToBytes (byte [] bytes, int offset, int count)
		{
			if (bytes == null)
				return null;

			if (count == 0)
				return new byte [0];

			int len = bytes.Length;
			if (offset < 0 || offset >= len)
				throw new ArgumentOutOfRangeException("offset");

			if (count < 0 || offset > len - count)
				throw new ArgumentOutOfRangeException("count");

			MemoryStream result = new MemoryStream ();
			int end = offset + count;
			for (int i = offset; i < end; i++){
				char c = (char) bytes [i];
				if (c == '+') {
					c = ' ';
				} else if (c == '%' && i < end - 2) {
					int xchar = GetChar (bytes, i + 1, 2);
					if (xchar != -1) {
						c = (char) xchar;
						i += 2;
					}
				}
				result.WriteByte ((byte) c);
			}

			return result.ToArray ();
		}

		public static string UrlEncode (byte [] bytes)
		{
			if (bytes == null)
				return null;

			if (bytes.Length == 0)
				return "";

			return Encoding.ASCII.GetString (UrlEncodeToBytes (bytes, 0, bytes.Length));
		}

		public static string UrlEncode (string str) 
		{
			return UrlEncode (str, Encoding.UTF8);
		}
	
		public static string UrlEncode (string s, Encoding Enc) 
		{
			if (s == null)
				return null;

			if (s == "")
				return "";

			bool needEncode = false;
			int len = s.Length;
			for (int i = 0; i < len; i++) {
				char c = s [i];
				if ((c < '0') || (c < 'A' && c > '9') || (c > 'Z' && c < 'a') || (c > 'z')) {
					if (NotEncoded (c))
						continue;

					needEncode = true;
					break;
				}
			}

			if (!needEncode)
				return s;

			// avoided GetByteCount call
			byte [] bytes = new byte[Enc.GetMaxByteCount(s.Length)];
			int realLen = Enc.GetBytes (s, 0, s.Length, bytes, 0);

			return Encoding.ASCII.GetString (UrlEncodeToBytes (bytes, 0, realLen));
		}
  
		public static string UrlEncode (byte [] bytes, int offset, int count)
		{
			if (bytes == null)
				return null;

			if (bytes.Length == 0)
				return "";

			return Encoding.ASCII.GetString (UrlEncodeToBytes (bytes, offset, count));
		}

		public static byte [] UrlEncodeToBytes (byte [] bytes)
		{
			if (bytes == null)
				return null;

			if (bytes.Length == 0)
				return new byte [0];

			return UrlEncodeToBytes (bytes, 0, bytes.Length);
		}

		public static byte [] UrlEncodeToBytes (string str)
		{
			return UrlEncodeToBytes (str, Encoding.UTF8);
		}

		public static byte [] UrlEncodeToBytes (string str, Encoding e)
		{
			if (str == null)
				return null;

			if (str == "")
				return new byte [0];

			byte [] bytes = e.GetBytes (str);

			return UrlEncodeToBytes (bytes, 0, bytes.Length);
		}

		public static byte [] UrlEncodeToBytes (byte [] bytes, int offset, int count)
		{
			if (bytes == null)
				return null;

			int len = bytes.Length;
			if (len == 0)
				return new byte [0];

			if (offset < 0 || offset >= len)
				throw new ArgumentOutOfRangeException("offset");

			if (count < 0 || count > len - offset)
				throw new ArgumentOutOfRangeException("count");

			MemoryStream result = new MemoryStream (count);
			int end = offset + count;
			for (int i = offset; i < end; i++)
				UrlEncodeChar ((char)bytes [i], result, false);

			return result.ToArray();
		}

		public static string UrlEncodeUnicode (string str)
		{
			if (str == null)
				return null;

			return Encoding.ASCII.GetString (UrlEncodeUnicodeToBytes (str));
		}

		public static byte [] UrlEncodeUnicodeToBytes (string str)
		{
			if (str == null)
				return null;

			if (str == "")
				return new byte [0];

			MemoryStream result = new MemoryStream (str.Length);
			foreach (char c in str){
				UrlEncodeChar (c, result, true);
			}

			return result.ToArray ();
		}

		public static string UrlPathEncode (string s)
		{
			if (s == null || s.Length == 0)
				return s;

			MemoryStream result = new MemoryStream ();
			int length = s.Length;
			for (int i = 0; i < length; i++) {
				UrlPathEncodeChar (s [i], result);
			}

			return Encoding.ASCII.GetString (result.ToArray ());
		}

		#endregion // Public Methods
	}
}