// ==========================================================================
// 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(decodedString, charset) {
	// Clear output field:
	//document.converter.encoded.value = "";
	
	//UTF-8 Default Charset
	charset = typeof(charset) != 'undefined' ? charset : 'utf8';
	
	// Some variables:
	var decoded = decodedString;
	var encoded = "";
	
	// ---------------- If ASCII character encoding was chosen: ----------------
	
	if (charset == "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:
		return 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 (charset == "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:
		return 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(encodedString, charset) {
	// Clear output field:
	//document.converter.decoded.value = "";

	//UTF-8 Default Charset
	charset = typeof(charset) != 'undefined' ? charset : 'utf8';
	
	// Some variables:
	var encoded = encodedString;
	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 (charset == "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:
		return 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 (charset == "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:
		return 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);
	}
}