generator.js

#! /usr/bin/env node
'use strict'

function loadCombinationList(charList, minCharCount, maxCharCount) {
    let comboList = [],
        charPos = [],
        currentCodeLength = minCharCount, //get the first code to work with as a starting point.
        currentCode = '',
        lastCharacterIndex = charList.length;

    //generate base charPos array
    for (let i = 0; i < maxCharCount; i++) {
        charPos.push(0);
    }

    while (currentCodeLength <= maxCharCount) {

        if (currentCode.indexOf('undefined') > -1) {
            break;
        }

        //build the code and increment the specific charpos array index
        currentCode = '';
        for (let i = 0; i < currentCodeLength; i++) {
            currentCode += charList[charPos[i]];
        }
        charPos[currentCodeLength-1]++;

        //save the code into the array
        comboList.push(currentCode);

        //now handle overflow - gotta go through array backwards
        let overflowCount = 0;
        for (let i = (charPos.length-1); i >= 0; i--) {
            if (charPos[i] >= lastCharacterIndex) {
                overflowCount++;
                charPos[i] = 0;

                //if our current index position isn't 0
                //increase the previous character
                if (i != 0) { charPos[i-1]++; }
            }
        }

        //do we need to increase character count?
        if (overflowCount === currentCodeLength) {
            currentCodeLength++;
        }

    }

    return comboList;

}

module.exports = loadCombinationList;