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Luhn.java
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90 lines (68 loc) · 2.24 KB
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import java.util.stream.IntStream;
public class Luhn {
private long number;
private long checkDigit;
private int[] addends;
private int checkSum;
private boolean isValid;
public Luhn(long number) {
this.number = number;
this.checkDigit = number % 10;
this.addends = generateAddends();
this.checkSum = IntStream.of(addends).sum();
this.isValid = checkSum % 10 == 0;
}
public long getCheckDigit() {
return checkDigit;
}
public int[] getAddends() {
return addends;
}
public int getCheckSum() {
return checkSum;
}
public boolean isValid() {
return isValid;
}
private int[] generateAddends() {
int[] reversedIntArray = splitToReversedIntArray(number);
for (int index = 1; index < reversedIntArray.length; index++) {
if (index % 2 != 0) {
reversedIntArray[index] = convertDigitForAddend(reversedIntArray[index]);
}
}
return reverseIntArray(reversedIntArray);
}
private static int[] splitToReversedIntArray(long value) {
int[] ints = new StringBuilder(Long.toString(value))
.reverse()
.toString()
.chars()
.map(x -> Character.getNumericValue(x))
.toArray();
return ints;
}
private static int convertDigitForAddend(int value) {
int doubled = value * 2;
return doubled < 10 ? doubled : doubled - 9;
}
public static long create(long number) {
long zeroCheckDigitNumber = number * 10;
Luhn luhn = new Luhn(zeroCheckDigitNumber);
if (luhn.isValid()) {
return zeroCheckDigitNumber;
}
return zeroCheckDigitNumber + createCheckDigit(luhn.getCheckSum());
}
private static int createCheckDigit(int value) {
int nearestTen = (int) (Math.ceil(value / 10.0) * 10);
return nearestTen - value;
}
private static int[] reverseIntArray(int[] array) {
int[] reversed = new int[array.length];
for (int index = 0; index < array.length; index++) {
reversed[index] = array[array.length - 1 - index];
}
return reversed;
}
}