Y-Tunnus tarkistus (Finnish business ID validator)

validate_finnish_business_id.php

<?php

function validate_company_id($company_id) {
  // Some old company id's have only 6 digits. They should be prefixed with 0.
  if (preg_match("/^[0-9]{6}\\-[0-9]{1}/", $company_id)) {
    $company_id = '0' . $company_id;
  }

  // Ensure that the company ID is entered in correct format.
  if (!preg_match("/^[0-9]{7}\\-[0-9]{1}/", $company_id)) {
    return FALSE;
  }

  list($id, $checksum) = explode('-', $company_id);
  $checksum = (int) $checksum;

  $total_count = 0;
  $multipliers = [7, 9, 10, 5, 8, 4, 2];
  foreach ($multipliers as $key => $multiplier) {
    $total_count = $total_count + $multiplier * $id[$key];
  }

  $remainder = $total_count % 11;

  // Remainder 1 is not valid.
  if ($remainder === 1) {
    return FALSE;
  }

  // Remainder 0 leads into checksum 0.
  if ($remainder === 0) {
    return $checksum === $remainder;
  }

  // If remainder is not 0, the checksum should be remainder deducted from 11.
  return $checksum === 11 - $remainder;
}