milojs/milo

'use strict';

// This would be the place to edit if you want a different
// Base32 implementation

var alphabet = '0123456789abcdefghjkmnpqrtuvwxyz';
var alias = { o:0, i:1, l:1, s:5 };
var DOLLAR = String.fromCharCode(36);

/**
 * Build a lookup table and memoize it
 *
 * Return an object that maps a character to its
 * byte value.
 */

var lookup = function() {
    var table = {};
    // Invert 'alphabet'
    for (var i = 0; i < alphabet.length; i++) {
        table[alphabet[i]] = i;
    }
    // Splice in 'alias'
    for (var key in alias) {
        if (!alias.hasOwnProperty(key)) continue;
        table[key] = table['' + alias[key]];
    }
    lookup = function() { return table; };
    return table;
};

/**
 * A streaming encoder
 *
 *     var encoder = new base32.Encoder()
 *     var output1 = encoder.update(input1)
 *     var output2 = encoder.update(input2)
 *     var lastoutput = encode.update(lastinput, true)
 */

function Encoder() {
    var skip = 0; // how many bits we will skip from the first byte
    var bits = 0; // 5 high bits, carry from one byte to the next

    this.output = '';

    // Read one byte of input
    // Should not really be used except by "update"
    this.readByte = function(byte) {
        // coerce the byte to an int
        if (typeof byte == 'string') byte = byte.charCodeAt(0);

        if (skip < 0) { // we have a carry from the previous byte
            bits |= (byte >> (-skip));
        } else { // no carry
            bits = (byte << skip) & 248;
        }

        if (skip > 3) {
            // not enough data to produce a character, get us another one
            skip -= 8;
            return 1;
        }

        if (skip < 4) {
            // produce a character
            this.output += alphabet[bits >> 3];
            skip += 5;
        }

        return 0;
    };

    // Flush any remaining bits left in the stream
    this.finish = function(check) {
        var output = this.output + (skip < 0 ? alphabet[bits >> 3] : '') + (check ? DOLLAR : '');
        this.output = '';
        return output;
    };
}

/**
 * Process additional input
 *
 * input: string of bytes to convert
 * flush: boolean, should we flush any trailing bits left
 *        in the stream
 * returns: a string of characters representing 'input' in base32
 */

Encoder.prototype.update = function(input, flush) {
    for (var i = 0; i < input.length; ) {
        i += this.readByte(input[i]);
    }
    // consume all output
    var output = this.output;
    this.output = '';
    if (flush) {
      output += this.finish();
    }
    return output;
};

// Functions analogously to Encoder

function Decoder() {
    var skip = 0; // how many bits we have from the previous character
    var byte = 0; // current byte we're producing

    this.output = '';

    // Consume a character from the stream, store
    // the output in this.output. As before, better
    // to use update().
    this.readChar = function(char) {
        if (typeof char != 'string'){
            if (typeof char == 'number') {
                char = String.fromCharCode(char);
            }
        }
        char = char.toLowerCase();
        var val = lookup()[char];
        if (typeof val == 'undefined') {
            // character does not exist in our lookup table
            return; // skip silently. An alternative would be:
            // throw Error('Could not find character "' + char + '" in lookup table.')
        }
        val <<= 3; // move to the high bits
        byte |= val >>> skip;
        skip += 5;
        if (skip >= 8) {
            // we have enough to preduce output
            this.output += String.fromCharCode(byte);
            skip -= 8;
            if (skip > 0) byte = (val << (5 - skip)) & 255;
            else byte = 0;
        }

    };

    this.finish = function(check) {
        var output = this.output + (check ? DOLLAR : '');
        this.output = '';
        return output;
    };
}

Decoder.prototype.update = function(input, flush) {
    for (var i = 0; i < input.length; i++) {
        this.readChar(input[i]);
    }
    var output = this.output;
    this.output = '';
    if (flush) {
      output += this.finish();
    }
    return output;
};

/** Convenience functions
 *
 * These are the ones to use if you just have a string and
 * want to convert it without dealing with streams and whatnot.
 */

// String of data goes in, Base32-encoded string comes out.
function encode(input) {
  var encoder = new Encoder();
  var output = encoder.update(input, true);
  return output;
}

// Base32-encoded string goes in, decoded data comes out.
function decode(input) {
    var decoder = new Decoder();
    var output = decoder.update(input, true);
    return output;
}

module.exports = {
    Decoder: Decoder,
    Encoder: Encoder,
    encode: encode,
    decode: decode
};