Gravity Form - Age Verification Function

age-verification.php

<?php

// 1 - Tie our validation function to the 'gform_validation' hook
add_filter('gform_validation_47', 'validate_vin');
function validate_vin($validation_result) {
    
    // 2 - Get the form object from the validation result
    $form = $validation_result["form"];
    
    // 3 - Get the current page being validated
    $current_page = rgpost('gform_source_page_number_' . $form['id']) ? rgpost('gform_source_page_number_' . $form['id']) : 1;
    
    // 4 - Loop through the form fields
    foreach($form['fields'] as &$field){
        
        // 5 - If the field does not have our designated CSS class, skip it
        if(strpos($field['cssClass'], 'validate-vin') === false)
            continue;
        
        // 6 - Get the field's page number
        $field_page = $field['pageNumber'];
        
        // 7 - Check if the field is hidden by GF conditional logic
        $is_hidden = RGFormsModel::is_field_hidden($form, $field, array());
        
        // 8 - If the field is not on the current page OR if the field is hidden, skip it
        if($field_page != $current_page || $is_hidden)
            continue;
        
        // 9 - Get the submitted value from the $_POST
        $field_value = rgpost("input_{$field['id']}");
        
        // 10 - Make a call to your validation function to validate the value
        $is_valid = is_vin($field_value);
        
        // 11 - If the field is valid we don't need to do anything, skip it
        if($is_valid)
            continue;
        
        // 12 - The field field validation, so first we'll need to fail the validation for the entire form
        $validation_result['is_valid'] = false;
        
        // 13 - Next we'll mark the specific field that failed and add a custom validation message
        $field['failed_validation'] = true;
        $field['validation_message'] = 'The VIN number you have entered is not valid.';
            
    }
    
    // 14 - Assign our modified $form object back to the validation result
    $validation_result['form'] = $form;
    
    // 15 - Return the validation result
    return $validation_result;
}

function is_vin($vin) {
    $vin = strtoupper(trim($vin));
    
    // check VIN length
    if (strlen($vin) != 17) {
        // error VIN is not 17 characters long
        return false;
    }
    
    // setup array of letter values
    $value['A'] = 1;
    $value['B'] = 2;
    $value['C'] = 3;
    $value['D'] = 4;
    $value['E'] = 5;
    $value['F'] = 6;
    $value['G'] = 7;
    $value['H'] = 8;
    $value['J'] = 1;
    $value['K'] = 2;
    $value['L'] = 3;
    $value['M'] = 4;
    $value['N'] = 5;
    $value['P'] = 7;
    $value['R'] = 9;
    $value['S'] = 2;
    $value['T'] = 3;
    $value['U'] = 4;
    $value['V'] = 5;
    $value['W'] = 6;
    $value['X'] = 7;
    $value['Y'] = 8;
    $value['Z'] = 9;
    
    // setup digit weights
    $weight[0] = 8; // 1st position
    $weight[1] = 7;
    $weight[2] = 6;
    $weight[3] = 5;
    $weight[4] = 4;
    $weight[5] = 3;
    $weight[6] = 2;
    $weight[7] = 10;
    $weight[8] = 0; // 9th position, this is the check digit
    $weight[9] = 9;
    $weight[10] = 8;
    $weight[11] = 7;
    $weight[12] = 6;
    $weight[13] = 5;
    $weight[14] = 4;
    $weight[15] = 3;
    $weight[16] = 2; // 17th position
    
    $char = str_split($vin); // split string into character array
    $total = 0;
    
    // loop though each character of the vin
    for ($i = 0; $i < 17; $i++) {
        if (is_numeric($char[$i])) {
            // use number
            // update total
            $total = $total + ($char[$i] * $weight[$i]);
        } elseif (array_key_exists($char[$i], $value)) {
            // use value of letter
            // update total
            $total = $total + ($value[$char[$i]] * $weight[$i]);
        } else {
            // error illegal character used
            return false;
        }
    }
    
    $mod = $total % 11; // find remainder after dividing by 11
    
    // if mod is 10 set the check_digit to X
    if ($mod == 10) {
        $checkDigit = 'X';
    } else {
        $checkDigit = $mod;
    }
    
    // check if the 9th character in the string (the check digit) equals the calculated value
    if ($char[8] == $checkDigit) { 
        // VIN is valid
        return true;
    } else {
        // VIN is not valid
        return false;
    }
}
?>