Access Code Generator & Validator

accesscode.js

// Access Code Generator & Validator

// API:
// string generateAccessCode()
// Boolean validateAccessCode(codeString)

(function () {

// configure:
var difference = 5;
var length = 12;

function startInt() {
	return Math.random() * 36 >> 0;
}

function nextInt(n) {
	var options = Math.ceil((36 - n) / difference);
	if (n < difference) options--;
	var a = n + Math.ceil(Math.random() * options) * difference;
	return a % 36;
}

function nextIntCanBe(curr, next) {
	var d = next - curr;
	if (d < 0) d += 36;
	return (d % difference) == 0;
}

function intToChar(i) {
	return String.fromCharCode(i + (i < 10 ? 48 : 55));
	//65-90 are LETTERS   
	//48-57 are numbers
}

function charToInt(c) {
	var n = c.charCodeAt(0);
	return n - (n < 65 ? 48 : 55);
}

generateAccessCode = function () {
	var chars = new Array(length);
	var r = startInt();
	for (var i = 0; i < length; i++) {
		r = nextInt(r);
		chars[i] = intToChar(r);
	}
	return chars.join("");
}

validateAccessCode = function (code) {
	if (code.length != length) {
		return false;
	}
	code = code.toUpperCase();
	var r = charToInt(code[0]);
	for (var i = 1; i < code.length - 1; i++) {
		if (!nextIntCanBe(r), r = charToInt(code[i])) {
			return false;
		}
	}
	return true;
}

})();