WP Simple Contact form

<?php
/**
 * Plugin Name: Very Simple Contact Form
 * Description: This is a very simple contact form. Use shortcode [contact] to display form on page. For more info please check readme file.
 * Version: 1.3
 * Author: Guido van der Leest
 * Author URI: http://www.guidovanderleest.nl
 * License: GNU General Public License v3 or later
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */


// Enqueues plugin scripts
function vscf_scripts() {
?><style>
#vscf label { display: block; margin: 10px 0; font-size: 1em;  color:#333; }
#vscf_name, #vscf_email, #vscf_subject { display: block; margin: 10px 0; border:1px solid #ccc; padding: 5px; font-size: 1em; width: 70%; }
#vscf_message { display: block; margin: 10px 0; border:1px solid #ccc; padding: 5px; font-size: 1em; width: 90%; }
#vscf_send { padding: 5px 10px; width: 8em; border:1px solid #ccc; background: #f8f8f8; color:#333; }
#vscf_send:hover { background: #f2f2f2; }
#vscf input.error { border-color: #e77776; }
#vscf textarea.error { border-color: #e77776; }
span.error { color: #e77776; }
span.hide { display:none; }
.info { clear:both; font-style: italic; font-size: 1.25em; }
</style><?php
}
add_action('wp_head', 'vscf_scripts');


// function to get the IP address of the user
function vscf_get_the_ip() {
    if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])) {
        return $_SERVER["HTTP_X_FORWARDED_FOR"];
    }
    elseif (isset($_SERVER["HTTP_CLIENT_IP"])) {
        return $_SERVER["HTTP_CLIENT_IP"];
    }
    else {
        return $_SERVER["REMOTE_ADDR"];
    }
}


// function to check inputfield
function vscf_clean_input($str){
    $str1 = preg_replace("/(\s){2,}/",'$1',$str);
    $allowed = "/[^a-z0-9\\040\\.\\-\\_\\\\]/i";
    $str1 = preg_replace($allowed,"",$str1);
    return $str1;
}

// the shortcode
function vscf_shortcode($atts) {
    extract(shortcode_atts(array(
        "email"                 => get_bloginfo('admin_email'),
        "subject"               => '',
        "label_name"            => __('Your name', 'verysimple') ,
        "label_email"           => __('Your email', 'verysimple') ,
        "label_subject"         => __('Subject', 'verysimple') ,
        "label_message"         => __('Message', 'verysimple') ,
        "label_submit"          => __('Submit', 'verysimple') ,
        "error_empty"           => __("Please fill in all the required fields", "verysimple"),
        "error_form_name"       => __('Please enter at least 3 characters', 'verysimple') ,
        "error_form_subject"        => __('Please enter at least 3 characters', 'verysimple') ,
        "error_form_message"        => __('Please enter at least 10 characters', 'verysimple') ,
        "error_email"           => __("Please enter a valid email", "verysimple"),
        "success"               => __("Thanks for your message! I will contact you as soon as I can.", "verysimple"),
    ), $atts));

    if (($_SERVER['REQUEST_METHOD'] == 'POST') && isset($_POST['form_send']) ) {

    // get posted data and sanitize them
        $post_data = array(
            'form_name'     => vscf_clean_input (sanitize_text_field($_POST['form_name'])),
            'email'         => sanitize_email($_POST['email']),
            'form_subject'      => vscf_clean_input (sanitize_text_field($_POST['form_subject'])),
            'form_message'      => vscf_clean_input (sanitize_text_field($_POST['form_message']))
        );

        $error = false;
        $required_fields = array("form_name", "email", "form_subject", "form_message");

        foreach ($required_fields as $required_field) {
            $value = stripslashes(trim($post_data[$required_field]));

        // displaying error message if validation failed for each input field
            if(((($required_field == "form_name") || ($required_field == "form_subject")) && strlen($value)<3) ||
                (($required_field == "form_message") && strlen($value)<10) || empty($value)) {
                $error_class[$required_field] = "error";
                $error_msg[$required_field] = ${"error_".$required_field};
                $error = true;
                $result = $error_empty;
            }
            $form_data[$required_field] = $value;
        }


        // sending email to admin
        if ($error == false) {
            $email_subject = "[" . get_bloginfo('name') . "] " . $form_data['form_subject'];
            $email_message = $form_data['form_message'] . "\n\nIP: " . vscf_get_the_ip();
            $headers  = "From: ".$form_data['form_name']." <".$form_data['email'].">\n";
            $headers .= "Content-Type: text/plain; charset=UTF-8\n";
            $headers .= "Content-Transfer-Encoding: 8bit\n";
            wp_mail($email, $email_subject, $email_message, $headers);
            $result = $success;
            $sent = true;
        }
    }

    // message
    if($result != "") {
        $info .= '<div class="info">'.$result.'</div>';
    }

    // the contact form with error messages
    $email_form = '<form class="vscf" id="vscf" method="post" action="">
        <div>
            <label for="vscf_name">'.$label_name.': <span class="error '.((isset($error_class['form_name']))?"":" hide").'" >'.$error_form_name.'</span></label>
            <input type="text" name="form_name" id="vscf_name" class="'.$error_class['form_name'].'" maxlength="50" value="'.$form_data['form_name'].'" />
        </div>
        <div>
            <label for="vscf_email">'.$label_email.': <span class="error '.((isset($error_class['email']))?"":" hide").'" >'.$error_email.'</span></label>
            <input type="text" name="email" id="vscf_email" class="'.$error_class['email'].'"  maxlength="50" value="'.$form_data['email'].'" />
        </div>
        <div>
            <label for="vscf_subject">'.$label_subject.': <span class="error '.((isset($error_class['form_subject']))?"":" hide").'" >'.$error_form_subject.'</span></label>
            <input type="text" name="form_subject" id="vscf_subject" maxlength="50"  class="'.$error_class['form_subject'].'"  value="'.$subject.$form_data['form_subject'].'" />
        </div>
        <div>
            <label for="vscf_message">'.$label_message.': <span class="error '.((isset($error_class['form_message']))?"":" hide").'" >'.$error_form_message.'</span></label>
            <textarea name="form_message" id="vscf_message" rows="10" class="'.$error_class['form_message'].'" >'.$form_data['form_message'].'</textarea>

        </div>
        <div>
            <input type="submit" value="'.$label_submit.'" name="form_send" id="vscf_send" />
        </div>
    </form>';

    if($sent == true) {
        return $info;
    } else {
        return $info.$email_form;
    }
}
add_shortcode('contact', 'vscf_shortcode');

?>


//Usage as shortcode
<?php [contact] ;?>
//Use directly into your theme
<?php echo do_shortcode('[contact]'); ?>