// ==========================================================================
// JavaScript Tool for URL Encoding/Decoding
// Copyright (C) 2006 Netzreport (netzreport.googlepages.com)
//
// Website: http://netzreport.googlepages.com/online_tool_for_url_en_decoding.html
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
//
// The GNU General Public License is also available from:
// http://www.gnu.org/copyleft/gpl.html
//
// A local copy of the GNU General Public License is available here:
// http://netzreport.googlepages.com/gpl.txt
// ==========================================================================
//
// --------------------------------------------------------------------------
// 2006-12-18: Changed character encoding. Now, one can choose between URL
//             encoding/decoding strings that are character encoded as ASCII
//             or UTF-8.
// 2006-11-19: First release
// --------------------------------------------------------------------------

// According to RFC 3986, only characters from a set of reserved and a set
// of unreserved characters are allowed in a URL:
var unreserved = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_.~";
var reserved = "!*'();:@&=+$,/?%#[]";
var allowed = unreserved + reserved;
var hexchars = "0123456789ABCDEFabcdef";

// --------------------------------- Encoding -------------------------------

// This function returns a percent sign followed by two hexadecimal digits.
// Input is a decimal value not greater than 255.
function gethex(decimal) {
  return "%" + hexchars.charAt(decimal >> 4) + hexchars.charAt(decimal & 0xF);
  }

function encode() {
	
	form = document.gs;
	
	// Clear output field
  form.encoded.value = "";

  // Some variables
  //var decoded = form.decoded.value;
  var decoded = form.q.value;
  var encoded = "";

  // ---------------- If ASCII character encoding was chosen: ----------------

  if (form.charset.value == "ascii") {

	// Remember non-ASCII characters, which will not be encoded
	var notascii = "";

	for (var i = 0; i < decoded.length; i++ ) {
	  var ch = decoded.charAt(i);
	  // Check if character is an unreserved character:
	  if (unreserved.indexOf(ch) != -1) {
		encoded = encoded + ch;
	  } else {
		// If position in the Unicode table is smaller than 128, then we have
		// an ASCII character:
		var charcode = decoded.charCodeAt(i);
		if (charcode < 128) {
		  encoded = encoded + gethex(charcode);
		} else {
		  encoded = encoded + ch;
		  notascii = notascii + ch + " ";
		}
	  }
	}

	// Write result
	form.encoded.value = encoded;

	// Display warning message if necessary
	if (notascii != "") alert("Warning: Non-ASCII characters in decoded text!\n\nThus, these characters have not been encoded:\n" + notascii);
  }

  // ---------------- If UTF-8 character encoding was chosen: ----------------

  if (form.charset.value == "utf8") {
	for (var i = 0; i < decoded.length; i++ ) {
	  var ch = decoded.charAt(i);
	  // Check if character is an unreserved character:
	  if (unreserved.indexOf(ch) != -1) {
		encoded = encoded + ch;
	  } else {

		// The position in the Unicode table tells us how many bytes are needed.
		// Note that if we talk about first, second, etc. in the following, we
		// are
		// counting from left to right:
		//
		// Position in | Bytes needed | Binary representation
		// Unicode table | for UTF-8 | of UTF-8
		// ----------------------------------------------------------
		// 0 - 127 | 1 byte | 0XXX.XXXX
		// 128 - 2047 | 2 bytes | 110X.XXXX 10XX.XXXX
		// 2048 - 65535 | 3 bytes | 1110.XXXX 10XX.XXXX 10XX.XXXX
		// 65536 - 2097151 | 4 bytes | 1111.0XXX 10XX.XXXX 10XX.XXXX 10XX.XXXX

		var charcode = decoded.charCodeAt(i);

		// Position 0 - 127 is equal to percent-encoding with an ASCII character
		// encoding:
		if (charcode < 128) {
		  encoded = encoded + gethex(charcode);
		}

		// Position 128 - 2047: two bytes for UTF-8 character encoding.
		if (charcode > 127 && charcode < 2048) {
		  // First UTF byte: Mask the first five bits of charcode with binary 110X.XXXX:
		  encoded = encoded + gethex((charcode >> 6) | 0xC0);
		  // Second UTF byte: Get last six bits of charcode and mask them with
			// binary 10XX.XXXX:
		  encoded = encoded + gethex((charcode & 0x3F) | 0x80);
		}

		// Position 2048 - 65535: three bytes for UTF-8 character encoding.
		if (charcode > 2047 && charcode < 65536) {
		  // First UTF byte: Mask the first four bits of charcode with binary 1110.XXXX:
		  encoded = encoded + gethex((charcode >> 12) | 0xE0);
		  // Second UTF byte: Get the next six bits of charcode and mask them
			// binary 10XX.XXXX:
		  encoded = encoded + gethex(((charcode >> 6) & 0x3F) | 0x80);
		  // Third UTF byte: Get the last six bits of charcode and mask them
			// binary 10XX.XXXX:
		  encoded = encoded + gethex((charcode & 0x3F) | 0x80);
		}

		// Position 65536 - : four bytes for UTF-8 character encoding.
		if (charcode > 65535) {
		  // First UTF byte: Mask the first three bits of charcode with binary 1111.0XXX:
		  encoded = encoded + gethex((charcode >> 18) | 0xF0);
		  // Second UTF byte: Get the next six bits of charcode and mask them
			// binary 10XX.XXXX:
		  encoded = encoded + gethex(((charcode >> 12) & 0x3F) | 0x80);
		  // Third UTF byte: Get the last six bits of charcode and mask them
			// binary 10XX.XXXX:
		  encoded = encoded + gethex(((charcode >> 6) & 0x3F) | 0x80);
		  // Fourth UTF byte: Get the last six bits of charcode and mask them
			// binary 10XX.XXXX:
		  encoded = encoded + gethex((charcode & 0x3F) | 0x80);
		}

	  }

	}  // end of for ...

	// Write result:
	form.encoded.value = encoded;
	form.q.value = encoded;
  }
}

// --------------------------------- Decoding -------------------------------

// This function returns the decimal value of two hexadecimal digits.
// Input is a percent sign followed by two hexadecimal digits. If the input
// string is shorter than three characters, the percent sign is missing or if
// not a hexadecimal numeral is used, then the decimal value 256 is returned:
function getdec(hexencoded) {
  if (hexencoded.length == 3) {
	if (hexencoded.charAt(0) == "%") {
	  if (hexchars.indexOf(hexencoded.charAt(1)) != -1 && hexchars.indexOf(hexencoded.charAt(2)) != -1) {
		return parseInt(hexencoded.substr(1,2),16);
	  }
	}
  }
  return 256;
}

function decode() {
  // Clear output field:
  form.decoded.value = "";

  // Some variables:
  var encoded = form.encoded.value;
  var decoded = "";
  // Remember characters that are not allowed in a URL:
  var notallowed = "";
  // Remember illegal percent encoding:
  var illegalencoding = "";

  // ---------------- If ASCII character encoding was chosen: ----------------
  if (form.charset.value == "ascii") {
	var i = 0;
	while (i < encoded.length) {
	  var ch = encoded.charAt(i);
	  // Check for percent-encoded string:
	  if (ch == "%") {
		// Check if percent-encoded string represents an ASCII character:
		if (getdec(encoded.substr(i,3)) < 128) {
		  decoded = decoded + unescape(encoded.substr(i,3));
		} else {
		  decoded = decoded + encoded.substr(i,3);
		  illegalencoding = illegalencoding + encoded.substr(i,3) + " ";
		}
		i = i + 3;
	  } else {
		// Check if character is an allowed character:
		if (allowed.indexOf(ch) == -1) notallowed = notallowed + ch + " ";
		decoded = decoded + ch;
		i++;
	  }
	}

	// Write result:
	form.decoded.value = decoded;

	// Display warning message if necessary:
	var warning = "";
	if (notallowed != "") warning = warning + "Characters not allowed in a URL:\n" + notallowed + "\n\n";
	if (illegalencoding != "") warning = warning + "Illegal percent-encoding (for ASCII):\n" + illegalencoding  + "\n\n";
	if (warning != "") alert("Warning: Illegal characters/strings in encoded text!\n\n" + warning);
  }

  // ---------------- If UTF-8 character encoding was chosen: ----------------
  if (form.charset.value == "utf8") {
	// UTF-8 bytes from left to right:
	var byte1, byte2, byte3, byte4 = 0;

	var i = 0;
	while (i < encoded.length) {
	  var ch = encoded.charAt(i);
	  // Check for percent-encoded string:
	  if (ch == "%") {

		// Check for legal percent-encoding of first byte:
		if (getdec(encoded.substr(i,3)) < 255) {

		  // Get the decimal values of all (potential) UTF-bytes:
		  byte1 = getdec(encoded.substr(i,3));
		  byte2 = getdec(encoded.substr(i+3,3));
		  byte3 = getdec(encoded.substr(i+6,3));
		  byte4 = getdec(encoded.substr(i+9,3));

		  // Check for one byte UTF-8 character encoding:
		  if (byte1 < 128) {
			decoded = decoded + String.fromCharCode(byte1);
			i = i + 3;
		  }

		  // Check for illegal one byte UTF-8 character encoding:
		  if (byte1 > 127 && byte1 < 192) {
			decoded = decoded + encoded.substr(i,3);
			illegalencoding = illegalencoding + encoded.substr(i,3) + " ";
			i = i + 3;
		  }

		  // Check for two byte UTF-8 character encoding:
		  if (byte1 > 191 && byte1 < 224) {
			if (byte2 > 127 && byte2 < 192) {
			  decoded = decoded + String.fromCharCode(((byte1 & 0x1F) << 6) | (byte2 & 0x3F));
			} else {
			  decoded = decoded + encoded.substr(i,6);
			  illegalencoding = illegalencoding + encoded.substr(i,6) + " ";
			}
			i = i + 6;
		  }

		  // Check for three byte UTF-8 character encoding:
		  if (byte1 > 223 && byte1 < 240) {
			if (byte2 > 127 && byte2 < 192) {
			  if (byte3 > 127 && byte3 < 192) {
				decoded = decoded + String.fromCharCode(((byte1 & 0xF) << 12) | ((byte2 & 0x3F) << 6) | (byte3 & 0x3F));
			  } else {
				decoded = decoded + encoded.substr(i,9);
				illegalencoding = illegalencoding + encoded.substr(i,9) + " ";
			  }
			} else {
			  decoded = decoded + encoded.substr(i,9);
			  illegalencoding = illegalencoding + encoded.substr(i,9) + " ";
			}
			i = i + 9;
		  }

		  // Check for four byte UTF-8 character encoding:
		  if (byte1 > 239) {
			if (byte2 > 127 && byte2 < 192) {
			  if (byte3 > 127 && byte3 < 192) {
				if (byte4 > 127 && byte4 < 192) {
				  decoded = decoded + String.fromCharCode(((byte1 & 0x7) << 18) | ((byte2 & 0x3F) << 12) | ((byte3 & 0x3F) << 6) | (byte4 & 0x3F));
				} else {
				  decoded = decoded + encoded.substr(i,12);
				  illegalencoding = illegalencoding + encoded.substr(i,12) + " ";
				}
			  } else {
				decoded = decoded + encoded.substr(i,12);
				illegalencoding = illegalencoding + encoded.substr(i,12) + " ";
			  }
			} else {
			  decoded = decoded + encoded.substr(i,12);
			  illegalencoding = illegalencoding + encoded.substr(i,12) + " ";
			}
			i = i + 12;
		  }

		} else {  // the first byte is not legally percent-encoded
		  decoded = decoded + encoded.substr(i,3);
		  illegalencoding = illegalencoding + encoded.substr(i,3) + " ";
		  i = i + 3;
		}

	  } else {  // the string is not percent encoded
		// Check if character is an allowed character:
		if (allowed.indexOf(ch) == -1) notallowed = notallowed + ch + " ";
		decoded = decoded + ch;
		i++;
	  }
	}  // end of while ...

	// Write result:
	form.decoded.value = decoded;

	// Display warning message if necessary:
	var warning = "";
	if (notallowed != "") warning = warning + "Characters not allowed in a URL:\n" + notallowed + "\n\n";
	if (illegalencoding != "") warning = warning + "Illegal percent-encoding (for UTF-8):\n" + illegalencoding  + "\n\n";
	if (warning != "") alert("Warning: Illegal characters/strings in encoded text!\n\n" + warning);
  }
}