btccom / cashaddress-js

let BigInteger = require('bigi')

let ALPHABET = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l'

// pre-compute lookup table

let SEPARATOR = ':'

let CSLEN = 8

let ALPHABET_MAP = {}

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

    let x = ALPHABET.charAt(z)

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

        throw new TypeError(x + ' is ambiguous')

    }

    ALPHABET_MAP[x] = z

}

function prefixChk (prefix) {

    let chk = new BigInteger('1')

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

        let c = prefix.charCodeAt(i)

        let 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

    let chk = prefixChk(prefix)

    let result = prefix + SEPARATOR

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

        let 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 (let i = 0; i < CSLEN; ++i) {

        chk = polymodStep(chk)

    }

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

    for (let i = 0; i < CSLEN; ++i) {

        let pos = 5 * (CSLEN - 1 - i)

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

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

    }

    return result

}

function decode (str) {

    if (str.length < 8) {

        throw new TypeError(str + ' too short')

    }

    if (str.length > 90) {

        throw new TypeError(str + ' too long')

    }

    // don't allow mixed case

    let lowered = str.toLowerCase()

    let uppered = str.toUpperCase()

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

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

    }

    str = lowered

    let 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)

    }

    let prefix = str.slice(0, split)

    let wordChars = str.slice(split + 1)

    if (wordChars.length < 6) {

        throw new Error('Data too short')

    }

    let chk = prefixChk(prefix)

    let words = []

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

        let c = wordChars.charAt(i)

        let 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, words }

}

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

    let value = 0

    let bits = 0

    let maxV = (1 << outBits) - 1

    let result = []

    for (let 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, encode, toWords, fromWords }