Page Comparison

def checkdigit(idWithoutCheckDigit) {
	idWithoutCheckDigit = idWithoutCheckDigit.trim().toUpperCase()
	sum = 0
	(0..<idWithoutCheckDigit.length()).each { i ->
    	char ch = idWithoutCheckDigit[-(i+1)]
    	if (!'0123456789ABCDEFGHIJKLMNOPQRSTUVYWXZ_'.contains(ch.toString()))
        	throw new Exception("$ch is an invalid character")
    	digit = (int)ch - 48;
    	sum += i % 2 == 0 ? 2*digit - (int)(digit/5)*9 : digit
  	}
	(10 - ((Math.abs(sum)+10) % 10)) % 10
}

// Validate our algorithm
assert checkdigit('12') == 5
assert checkdigit('123') == 0
assert checkdigit('1245496594') == 3
assert checkdigit('TEST') == 4
assert checkdigit('Test123') == 7
assert checkdigit('00012') == 5
assert checkdigit('9') == 1
assert checkdigit('999') == 3
assert checkdigit('999999') == 6
assert checkdigit('CHECKDIGIT') == 7
assert checkdigit('EK8XO5V9T8') == 2
assert checkdigit('Y9IDV90NVK') == 1
assert checkdigit('RWRGBM8C5S') == 5
assert checkdigit('OBYY3LXR79') == 5
assert checkdigit('Z2N9Z3F0K3') == 2
assert checkdigit('ROBL3MPLSE') == 9
assert checkdigit('VQWEWFNY8U') == 9
assert checkdigit('45TPECUWKJ') == 1
assert checkdigit('6KWKDFD79A') == 8
assert checkdigit('HXNPKGY4EX') == 3
assert checkdigit('91BT') == 2
try {
checkdigit ("12/3")
assert false
} catch(e) { }