Credit Card Class

<?php

class credit{

        function credit(){

        }

        function validate($cc_number, $cvv2, $date){
                $this->validateCard($cc_number);
                $this->validateExDate($date);
                $this->validateCVV($cc_number, $cvv2);
        }

        function validateCard($cc_number){
                global $e;

                $first_number = substr($cc_number, 0, 1);
                switch ($first_number){
                        case 3:
                                if (!preg_match('/^3\d{3}[ \-]?\d{6}[ \-]?\d{5}$/', $cc_number)) $e->setError("American Express number is not valid");
                                break;
                        case 4:
                                if (!preg_match('/^4\d{3}[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $cc_number)) $e->setError("Visa number is not valid");
                                break;
                        case 5:
                                if (!preg_match('/^5\d{3}[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $cc_number)) $e->setError("MasterCard number is not valid");
                                break;
                        case 6:
                                if (!preg_match('/^6011[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $cc_number)) $e->setError("Discover Card number is not valid");
                                break;
                        default:
                                 $e->setError("Credit Card number is not valid: Error 1");
                                 break;
                }

                if($e->countErrors() == 0) $this->validateCard2($cc_number);

        }

        function validateCard2($cc_number){
                global $e;

                $checksum = 0;

                $j = 1;

                for ($i = strlen($cc_number) - 1; $i >= 0; $i--){

                        $calc = substr($cc_number, $i, 1) * $j;

                        if ($calc > 9){
                                $checksum = $checksum + 1;
                                $calc     = $calc - 10;
                        }

                        $checksum += $calc;

                        if ($j == 1){
                                $j = 2;
                        }else{
                                $j = 1;
                        }
                }

                if ($checksum % 10 != 0) $e->setError("Credit Card number is not valid: Error 2");
        }

        function validateExDate($date){
                global $e;

                $month =  substr($date, 0, 2);
                $year =  substr($date, 2, 2);

                $current_month = date("m");
                $current_year  = date("y");
                if ($year < $current_year){
                        $e->setError("Expiration Date is not valid : Error 3");
                }else{
                        if ($year == $current_year)
                        {
                                if ($month < $current_month){
                                        $e->setError("Expiration Date is not valid : Error 4");
                                }
                        }
                }
        }

        function validateCVV($cc_number, $cvv2){
                global $e;

                $first_number = substr($cc_number, 0, 1);

                if ($first_number == 3){
                        if (!preg_match("/^\d{4}$/", $cvv2)) $e->setError("CVV number is not valid : Error 5");
                }else{
                        if (!preg_match("/^\d{3}$/", $cvv2)) $e->setError("CVV number is not valid : Error 6");
                }
        }

        function maskCard($cc_number){
                $count = strlen($cc_number);
                for($i = 1; $i <= ($count -4); $i++){
                        echo "X";
                }
                echo substr($cc_number, -4);
        }

}

?>


<?php

        require_once "class.error.php";
    $e = new error;
        require_once "class.credit.php";
        $cc = new credit;

        if($_POST){
                $cc_number = $_POST['cc_number'];
                $expire_month = $_POST['expire_month'];
                $expire_year = $_POST['expire_year'];
                $cc_cvv = $_POST['cc_cvv'];

                $date = $expire_month . $expire_year;
                $cc->validate($cc_number, $cc_cvv, $date);

                if($e->countErrors() == 0){
                        //process form
                        header("location: somewhere.php");
                        die();
                }
        }

?>

    <?php $e->showErrors(); ?>
        <form method="post" action="<?php echo $_SERVER['PHP_SELF'] ?>">
    <table border="0" cellpadding="4" width="450">
      <tr>
        <td width="200" class="tbl_left">Payment Type: </td>
        <td width="250" class="tbl_right">Credit Card</td>
      </tr>
      <tr>
        <td class="tbl_left">Card Holder Name: </td>
        <td class="tbl_right"><input type="text" name="cc_name" /></td>
      </tr>
      <tr>
        <td class="tbl_left">Card Type: </td>
        <td class="tbl_right"><select name="cc_type">
        <option value="American Express">American Express</option>
        <option value="Discover">Discover</option>
        <option value="Master Card">Master Card</option>
        <option value="Visa">Visa</option>
    </select>
    </td>
      </tr>
      <tr>
        <td class="tbl_left">Credit Card Number: </td>
        <td class="tbl_right"><input type="text" name="cc_number" /></td>
      </tr>
      <tr>
        <td class="tbl_left">Expiration Date: </td>
        <td class="tbl_right"><select name="expire_month">
    <option value="01">January</option>
    <option value="02">February</option>
    <option value="03">March</option>
    <option value="04">April</option>
    <option value="05">May</option>
    <option value="06">June</option>
    <option value="07">July</option>
    <option value="08">August</option>
    <option value="09">September</option>
    <option value="10">October</option>
    <option value="11">November</option>
    <option value="12">December</option>
    </select>
    <select name="expire_year">
    <?php
    for($x=date(Y); $x<=2050; $x++){
    echo '<option value="'.substr($x, -2).'">'.$x.'</option>'."\n";
    }
    ?>
    </select>
    </td>
      </tr>
      <tr>
        <td class="tbl_left">CVV Number:</td>
        <td class="tbl_right"><input type="text" name="cc_cvv" size="5" maxlength="4" /></td>
      </tr>
      <tr>
        <td class="tbl_left">Enter a Promo Code: </td>
        <td class="tbl_right"><input type="text" name="promo_code" /></td>
      </tr>
    </table>
</form>


echo $cc->maskCard($cc_number);