const ALPHABET = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz';
const ALPHABET_MAP = {};

for(let i = 0; i < ALPHABET.length; i++)
    ALPHABET_MAP[ALPHABET.charAt(i)] = i;

const BASE = 58;

module.exports.encode58 = function (buffer) {
    if(buffer.length === 0)
        return '';

    let i;
    let j;

    const digits = [0];

    for(i = 0; i < buffer.length; i++) {
        for(j = 0; j < digits.length; j++)
            digits[j] <<= 8;

        digits[0] += buffer[i];
        let carry = 0;

        for(j = 0; j < digits.length; ++j) {
            digits[j] += carry;
            carry = (digits[j] / BASE) | 0;
            digits[j] %= BASE
        }

        while (carry) {
            digits.push(carry % BASE);
            carry = (carry / BASE) | 0
        }
    }

    for(i = 0; buffer[i] === 0 && i < buffer.length - 1; i++)
        digits.push(0);

    return digits.reverse().map(digit => ALPHABET[digit]).join('');
};

module.exports.decode58 = function (string) {
    if(string.length === 0)
        return [];

    let i;
    let j;

    const bytes = [0];

    for(i = 0; i < string.length; i++) {
        const c = string[i];

        if(!(c in ALPHABET_MAP))
            throw new Error('Non-base58 character');

        for(j = 0; j < bytes.length; j++)
            bytes[j] *= BASE;

        bytes[0] += ALPHABET_MAP[c];
        let carry = 0;

        for(j = 0; j < bytes.length; ++j) {
            bytes[j] += carry;
            carry = bytes[j] >> 8;
            bytes[j] &= 0xff;
        }

        while (carry) {
            bytes.push(carry & 0xff);
            carry >>= 8;
        }
    }

    for(i = 0; string[i] === '1' && i < string.length - 1; i++)
        bytes.push(0);

    return bytes.reverse();
};