calculateIsbn13CheckDigit static method

int? calculateIsbn13CheckDigit(
  1. DigitString input
)

Implementation

static int? calculateIsbn13CheckDigit(DigitString input) {
  const weights = [1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3];

  var inputList = input.intList;

  if (input.length != 13) {
    return null;
  }

  var sumProd = 0;
  for (var i = 0; i < 12; i++) {
    sumProd += inputList[i] * weights[i];
  }
  return (10 - sumProd % 10) % 10;
}