<?php
  namespace Foxx\ComputerScience\U1;

  final class SinCheck {

    public function __construct() {
      echo "Welcome to the sin checker!\n";
      $userInput = readline("Enter your 9 digit SIN: ");

      $valid = $this->validateSIN($userInput);

      if ($valid) {
        echo "Your SIN is valid.";
      } else {
        echo "Your SIN is invalid.";
      }
    }

    /**
     * The luhn algorithm is used to check the validity of a number.
     *
     * @param string $str
     * @return bool
     */
    function luhn(string $str): bool {
      $odd = !strlen($str)%2;
      $sum = 0;
      for($i=0;$i<strlen($str);++$i){
        $n=0+$str[$i];
        $odd=!$odd;
        if($odd){
          $sum+=$n;
        }else{
          $x=2*$n;
          $sum+=$x>9?$x-9:$x;
        }
      }
      return(($sum%10)==0);
    }

    /**
     * Checks if the given string is a valid SIN.
     *
     * @param string $str
     * @return bool
     */
    function validateSIN(string $sin): bool {
      $sin = preg_replace('/[^0-9]/','',$sin);
      if(strlen($sin) == 9){
        if($sin[0] == '0' || $sin[0] == '8'){
          return false;
        }else{
          return $this->luhn($sin);
        }
      }else{
        return false;
      }
    }

    /**
     * Generates a random SIN.
     *
     * @param string $separator
     * @return string
     */
    function generateSIN(string $separator = ' '){
      $validPrefix = array(1,2,3,4,5,6,7,9);
      $sin = array_rand($validPrefix,1);
      $length = 9;

      while(strlen($sin) < ($length - 1)){
        $sin .= rand(0,9);
      }

      $sum = 0;
      $pos = 0;

      $reversedSIN = strrev( $sin );

      while($pos < $length - 1){
        $odd = $reversedSIN[ $pos ] * 2;
        if($odd > 9){
          $odd -= 9;
        }

        $sum += $odd;

        if($pos != ($length - 2)){
          $sum += $reversedSIN[ $pos +1 ];
        }
        $pos += 2;
      }

      $checkdigit = (( floor($sum/10) + 1) * 10 - $sum) % 10;
      $sin .= $checkdigit;

      $sin1 = substr($sin,0,3);
      $sin2 = substr($sin,3,3);
      $sin3 = substr($sin,6,3);

      return $sin1.$separator.$sin2.$separator.$sin3;
    }
  }