converter.js

'use strict';

/**
 * Converter
 *
 * @param {string|Array} srcAlphabet
 * @param {string|Array} dstAlphabet
 * @constructor
 */
function Converter(srcAlphabet, dstAlphabet) {
    if (!srcAlphabet || !dstAlphabet || !srcAlphabet.length || !dstAlphabet.length) {
        throw new Error('Bad alphabet');
    }
    this.srcAlphabet = srcAlphabet;
    this.dstAlphabet = dstAlphabet;
}

/**
 * Convert number from source alphabet to destination alphabet
 *
 * @param {string|Array} number - number represented as a string or array of points
 *
 * @returns {string|Array}
 */
Converter.prototype.convert = function(number) {
    var i, divide, newlen,
    numberMap = {},
    fromBase = this.srcAlphabet.length,
    toBase = this.dstAlphabet.length,
    length = number.length,
    result = typeof number === 'string' ? '' : [];

    if (!this.isValid(number)) {
        throw new Error('Number "' + number + '" contains of non-alphabetic digits (' + this.srcAlphabet + ')');
    }

    if (this.srcAlphabet === this.dstAlphabet) {
        return number;
    }

    for (i = 0; i < length; i++) {
        numberMap[i] = this.srcAlphabet.indexOf(number[i]);
    }
    do {
        divide = 0;
        newlen = 0;
        for (i = 0; i < length; i++) {
            divide = divide * fromBase + numberMap[i];
            if (divide >= toBase) {
                numberMap[newlen++] = parseInt(divide / toBase, 10);
                divide = divide % toBase;
            } else if (newlen > 0) {
                numberMap[newlen++] = 0;
            }
        }
        length = newlen;
        result = this.dstAlphabet.slice(divide, divide + 1).concat(result);
    } while (newlen !== 0);

    return result;
};

/**
 * Valid number with source alphabet
 *
 * @param {number} number
 *
 * @returns {boolean}
 */
Converter.prototype.isValid = function(number) {
    var i = 0;
    for (; i < number.length; ++i) {
        if (this.srcAlphabet.indexOf(number[i]) === -1) {
            return false;
        }
    }
    return true;
};

module.exports = Converter;