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luhn.dart
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luhn.dart
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#library('luhn');
#import('util.dart');
class Luhn {
final DOUBLE_DIGITS = const [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];
final C_0;
final C_9;
Luhn() : C_0 = '0'.charCodeAt(0), C_9 = '9'.charCodeAt(0);
bool testIt(List a, num startAt, num maxLen) {
var total = 0;
var doubleDigit = false;
for (var i = startAt + maxLen - 1; i >= startAt; i--) {
total += doubleDigit ? DOUBLE_DIGITS[a[i]] : a[i];
doubleDigit = !doubleDigit;
}
return total % 10 == 0;
}
String mask(String s) {
var masked = null;
var i = 0;
var digitCount = 0;
var digits = [];
var len = s.length;
while (i < len) {
var c = s[i];
var cc = c.charCodeAt(0);
if (cc >= C_0 && cc <= C_9) {
digitCount += 1;
digits.add(Math.parseInt(c));
if (digitCount >= 14) {
for (var theLen = digitCount < 16 ? digitCount : 16; theLen >= 14; theLen--) {
var startAt = digitCount - theLen;
if (testIt(digits, startAt, theLen)) {
if (masked === null) { masked = s.splitChars(); }
var j = i;
var maskLen = theLen;
while (maskLen > 0) {
var mc = s.charCodeAt(j);
if (mc >= C_0 && mc <= C_9) {
masked[j] = 'X';
maskLen -= 1;
}
j -= 1;
}
}
}
}
} else if (c == '-' || c == ' ') {
// Keep going.
} else {
if (digitCount > 0) {
digitCount = 0;
digits = [];
}
}
i += 1;
}
return masked !== null ? Strings.concatAll(masked) : s;
}
void tapStdin() {
var s;
var ios = new StringInputStream(stdin);
var lines = [];
while ((s = ios.readLine()) !== null) {
lines.add(s);
}
var args = new Options().arguments;
var nRepeats = args.length > 0 ? Math.parseInt(args[0]) : 1;
for (var i = 0; i < nRepeats; i++) {
for (s in lines) {
print(mask(s));
}
}
exit(0);
}
}