btccom / cashaddress-js

var BigInteger = require('bigi');

var ALPHABET = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l';

// pre-compute lookup table

var SEPARATOR = ':';

var CSLEN = 8;

var ALPHABET_MAP = {};

for (var z = 0; z < ALPHABET.length; z++) {

    var x = ALPHABET.charAt(z);

    if (ALPHABET_MAP[x] !== undefined) {

        throw new TypeError(x + ' is ambiguous');

    }

    ALPHABET_MAP[x] = z;

}

function polymodStep(pre) {

    var b = pre.shiftRight(35);

    var mask = BigInteger.fromHex('07ffffffff');

    var v = pre.and(mask).shiftLeft(new BigInteger('5'));

    if (b.and(new BigInteger('1')).intValue() > 0) {

        v = v.xor(BigInteger.fromHex('98f2bc8e61'));

    }

    if (b.and(new BigInteger('2')).intValue()) {

        v = v.xor(BigInteger.fromHex('79b76d99e2'));

    }

    if (b.and(new BigInteger('4')).intValue()) {

        v = v.xor(BigInteger.fromHex('f33e5fb3c4'));

    }

    if (b.and(new BigInteger('8')).intValue()) {

        v = v.xor(BigInteger.fromHex('ae2eabe2a8'));

    }

    if (b.and(new BigInteger('16')).intValue()) {

        v = v.xor(BigInteger.fromHex('1e4f43e470'));

    }

    return v;

}

function prefixChk(prefix) {

    var chk = new BigInteger('1');

    for (var i = 0; i < prefix.length; ++i) {

        var c = prefix.charCodeAt(i);

        var mixwith = new BigInteger('' + (c & 0x1f));

        chk = polymodStep(chk).xor(mixwith);

    }

    chk = polymodStep(chk);

    return chk;

}

function encode(prefix, words) {

    // too long?

    if (prefix.length + CSLEN + 1 + words.length > 90) {

        throw new TypeError('Exceeds Base32 maximum length');

    }

    prefix = prefix.toLowerCase();

    // determine chk mod

    var chk = prefixChk(prefix);

    var result = prefix + SEPARATOR;

    for (var i = 0; i < words.length; ++i) {

        var _x = words[i];

        if (_x >>> 5 !== 0) {

            throw new Error('Non 5-bit word');

        }

        chk = polymodStep(chk).xor(new BigInteger('' + _x));

        result += ALPHABET.charAt(_x);

    }

    for (var _i = 0; _i < CSLEN; ++_i) {

        chk = polymodStep(chk);

    }

    chk = chk.xor(new BigInteger('1'));

    for (var _i2 = 0; _i2 < CSLEN; ++_i2) {

        var pos = 5 * (CSLEN - 1 - _i2);

        var v2 = chk.shiftRight(new BigInteger('' + pos)).and(BigInteger.fromHex('1f'));

        result += ALPHABET.charAt(v2.toString(10));

    }

    return result;

}

function decode(str) {

    // don't allow mixed case

    var lowered = str.toLowerCase();

    var uppered = str.toUpperCase();

    if (str !== lowered && str !== uppered) {

        throw new Error('Mixed-case string ' + str);

    }

    str = lowered;

    var split = str.lastIndexOf(SEPARATOR);

    if (split === -1) {

        throw new Error('No separator character for ' + str);

    }

    if (split === 0) {

        throw new Error('Missing prefix for ' + str);

    }

    var prefix = str.slice(0, split);

    var wordChars = str.slice(split + 1);

    if (wordChars.length < 6) {

        throw new Error('Data too short');

    }

    var chk = prefixChk(prefix);

    var words = [];

    for (var i = 0; i < wordChars.length; ++i) {

        var c = wordChars.charAt(i);

        var v = ALPHABET_MAP[c];

        if (v === undefined) {

            throw new Error('Unknown character ' + c);

        }

        chk = polymodStep(chk).xor(new BigInteger('' + v));

        // not in the checksum?

        if (i + CSLEN >= wordChars.length) {

            continue;

        }

        words.push(v);

    }

    if (chk.toString(10) !== '1') {

        throw new Error('Invalid checksum for ' + str);

    }

    return { prefix: prefix, words: words };

}

function convert(data, inBits, outBits, pad) {

    var value = 0;

    var bits = 0;

    var maxV = (1 << outBits) - 1;

    var result = [];

    for (var i = 0; i < data.length; ++i) {

        value = value << inBits | data[i];

        bits += inBits;

        while (bits >= outBits) {

            bits -= outBits;

            result.push(value >>> bits & maxV);

        }

    }

    if (pad) {

        if (bits > 0) {

            result.push(value << outBits - bits & maxV);

        }

    } else {

        if (bits >= inBits) {

            throw new Error('Excess padding');

        }

            throw new Error('Non-zero padding');

        }

    }

    return result;

}

function toWords(bytes) {

    return convert(bytes, 8, 5, true);

}

function fromWords(words) {

    return convert(words, 5, 8, false);

}

module.exports = { decode: decode, encode: encode, toWords: toWords, fromWords: fromWords };