/*
Copyright (c) 2010 Thomas Peri
http://www.tumuski.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.
*/

/*jslint white: true, browser: true, onevar: true, undef: true, nomen: true,
	eqeqeq: true, plusplus: true, regexp: true, newcap: true, immed: true */
// (good parts minus bitwise and strict, plus white.)

/**
 * Nibbler - Multi-Base Encoder
 *
 * version 2010-04-07
 *
 * Options:
 *   dataBits: The number of bits in each character of unencoded data.
 *   codeBits: The number of bits in each character of encoded data.
 *   keyString: The characters that correspond to each value when encoded.
 *   pad (optional): The character to pad the end of encoded output.
 *   arrayData (optional): If truthy, unencoded data is an array instead of a string.
 *
 * Example:
 *
 * var base64_8bit = new Nibbler({
 *     dataBits: 8,
 *     codeBits: 6,
 *     keyString: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
 *     pad: '='
 * });
 * base64_8bit.encode("Hello, World!");  // returns "SGVsbG8sIFdvcmxkIQ=="
 * base64_8bit.decode("SGVsbG8sIFdvcmxkIQ==");  // returns "Hello, World!"
 *
 * var base64_7bit = new Nibbler({
 *     dataBits: 7,
 *     codeBits: 6,
 *     keyString: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
 *     pad: '='
 * });
 * base64_7bit.encode("Hello, World!");  // returns "kZdmzesQV9/LZkQg=="
 * base64_7bit.decode("kZdmzesQV9/LZkQg==");  // returns "Hello, World!"
 *
 */
var Nibbler = function (options) {
    var construct,

    // options
    pad, dataBits, codeBits, keyString, arrayData,

    // private instance variables
    mask, group, max,

    // private methods
    gcd, translate,

    // public methods
    encode, decode;

    // pseudo-constructor
    construct = function () {
        var i, mag, prev;

        // options
        pad = options.pad || '';
        dataBits = options.dataBits;
        codeBits = options.codeBits;
        keyString = options.keyString;
        arrayData = options.arrayData;

        // bitmasks
        mag = Math.max(dataBits, codeBits);
        prev = 0;
        mask = [];
        for (i = 0; i < mag; i += 1) {
            mask.push(prev);
            prev += prev + 1;
        }
        max = prev;

        // ouput code characters in multiples of this number
        group = dataBits / gcd(dataBits, codeBits);
    };

    // greatest common divisor
    gcd = function (a, b) {
        var t;
        while (b !== 0) {
            t = b;
            b = a % b;
            a = t;
        }
        return a;
    };

    // the re-coder
    translate = function (input, bitsIn, bitsOut, decoding) {
        var i, len, chr, byteIn,
        buffer, size, output,
        write;

        // append a byte to the output
        write = function (n) {
            if (!decoding) {
                output.push(keyString.charAt(n));
            } else if (arrayData) {
                output.push(n);
            } else {
                output.push(String.fromCharCode(n));
            }
        };

        buffer = 0;
        size = 0;
        output = [];

        len = input.length;
        for (i = 0; i < len; i += 1) {
            // the new size the buffer will be after adding these bits
            size += bitsIn;

            // read a character
            if (decoding) {
                // decode it
                chr = input.charAt(i);
                byteIn = keyString.indexOf(chr);
                if (chr === pad) {
                    break;
                } else if (byteIn < 0) {
                    throw 'the character "' + chr + '" is not a member of ' + keyString;
                }
            } else {
                if (arrayData) {
                    byteIn = input[i];
                } else {
                    byteIn = input.charCodeAt(i);
                }
                if ((byteIn | max) !== max) {
                    throw byteIn + " is outside the range 0-" + max;
                }
            }

            // shift the buffer to the left and add the new bits
            buffer = (buffer << bitsIn) | byteIn;

            // as long as there's enough in the buffer for another output...
            while (size >= bitsOut) {
                // the new size the buffer will be after an output
                size -= bitsOut;

                // output the part that lies to the left of that number of bits
                // by shifting the them to the right
                write(buffer >> size);

                // remove the bits we wrote from the buffer
                // by applying a mask with the new size
                buffer &= mask[size];
            }
        }

        // If we're encoding and there's input left over, pad the output.
        // Otherwise, leave the extra bits off, 'cause they themselves are padding
        if (!decoding && size > 0) {

            // flush the buffer
            write(buffer << (bitsOut - size));

            // add padding keyString for the remainder of the group
            len = output.length % group;
            for (i = 0; i < len; i += 1) {
                output.push(pad);
            }
        }

        // string!
        return (arrayData && decoding) ? output : output.join('');
    };

    /**
	 * Encode.  Input and output are strings.
	 */
    encode = function (input) {
        return translate(input, dataBits, codeBits, false);
    };

    /**
	 * Decode.  Input and output are strings.
	 */
    decode = function (input) {
        return translate(input, codeBits, dataBits, true);
    };

    this.encode = encode;
    this.decode = decode;
    construct();
};