Class EAN13

EAN13.php

class EAN13 {

    protected $code;

    public function __construct($code)
    {
        if (preg_match("/^[0-9]{12}$/", $code))
        {
            $this->code = $code . $this->calculateChecksumNumber($code);
        }

        elseif(preg_match("/^[0-9]{13}$/", $code))
        {
            if($this->calculateChecksumNumber(substr($code, 0, -1)) != $code[12])
            {
                throw new \InvalidArgumentException("Invalid EAN code.");
            }

            $this->code = $code;
        }
        else
        {
            throw new \InvalidArgumentException("Parameter must be 12 or 13 digits.");
        }
    }

    public function toString()
    {
        return $this->code;
    }

    protected function calculateChecksumNumber($code)
    {
        $even_sum = $code{1} + $code{3} + $code{5} + $code{7} + $code{9} + $code{11};
        $odd_sum = $code{0} + $code{2} + $code{4} + $code{6} + $code{8} + $code{10};

        $even_sum_three = $even_sum * 3;
        $total_sum = $even_sum_three + $odd_sum;

        $next_ten = (ceil($total_sum/10))*10;

        return $next_ten - $total_sum;
    }

}