Bootstrap Ajax Contact Form

contact.html

<form id="contact-form" method="post" action="mailer.php" role="form">

    <div class="messages"></div>

    <div class="controls">

        <div class="row">
            <div class="col-md-6">
                <div class="form-group">
                    <label for="form_name">Firstname *</label>
                    <input id="form_name" type="text" name="name" class="form-control" placeholder="Please enter your firstname *" required="required" data-error="Firstname is required.">
                    <div class="help-block with-errors"></div>
                </div>
            </div>
            <div class="col-md-6">
                <div class="form-group">
                    <label for="form_lastname">Lastname *</label>
                    <input id="form_lastname" type="text" name="surname" class="form-control" placeholder="Please enter your lastname *" required="required" data-error="Lastname is required.">
                    <div class="help-block with-errors"></div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-6">
                <div class="form-group">
                    <label for="form_email">Email *</label>
                    <input id="form_email" type="email" name="email" class="form-control" placeholder="Please enter your email *" required="required" data-error="Valid email is required.">
                    <div class="help-block with-errors"></div>
                </div>
            </div>
            <div class="col-md-6">
                <div class="form-group">
                    <label for="form_phone">Phone</label>
                    <input id="form_phone" type="tel" name="phone" class="form-control" placeholder="Please enter your phone">
                    <div class="help-block with-errors"></div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-12">
                <div class="form-group">
                    <label for="form_message">Message *</label>
                    <textarea id="form_message" name="message" class="form-control" placeholder="Message for me *" rows="4" required="required" data-error="Please,leave us a message."></textarea>
                    <div class="help-block with-errors"></div>
                </div>
            </div>
            <div class="col-md-12">
                <input type="submit" class="btn btn-success btn-send" value="Send message">
            </div>
        </div>
        <div class="row">
            <div class="col-md-12">
                <p class="text-muted"><strong>*</strong> These fields are required.</p>
            </div>
        </div>
    </div>

</form>

mailer.js

$(document).ready( function() {

    $('#contact-form').validator();

    $('#contact-form').on('submit', function (e) {

        e.preventDefault();

        $.ajax({

            type: "POST",
            url: "mailer.php",
            data: $(this).serialize()

        }).done( function (data) {

                var messageAlert = 'alert-' + data.type;
                var messageText = data.message;

                var alertBox = '<div class="alert ' + messageAlert + ' alert-dismissable"><button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>' + messageText + '</div>';
                if (messageAlert && messageText) {
                    $('#contact-form').find('.messages').html(alertBox);
                    $('#contact-form')[0].reset();
                }
            })
        })
    });
});

mailer.php

<?php

// configure
$from = '[email protected]';
$sendTo = '[email protected]';
$subject = 'New message from contact form';
$fields = array('name' => 'Name', 'surname' => 'Surname', 'phone' => 'Phone', 'email' => 'Email', 'message' => 'Message'); // array variable name => Text to appear in the email
$okMessage = 'Contact form successfully submitted. Thank you, I will get back to you soon!';
$errorMessage = 'There was an error while submitting the form. Please try again later';

// let's do the sending
try
{
    $emailText = "You have new message from contact form\n=============================\n";

    foreach ($_POST as $key => $value) {

        if (isset($fields[$key])) {
            $emailText .= "$fields[$key]: $value\n";
        }
    }

    $headers = array('Content-Type: text/plain; charset="UTF-8";',
        'From: ' . $from,
        'Reply-To: ' . $from,
        'Return-Path: ' . $from,
    );

    mail($sendTo, $subject, $emailText, implode("\n", $headers));

    $responseArray = array('type' => 'success', 'message' => $okMessage);
}
catch (\Exception $e)
{
    $responseArray = array('type' => 'danger', 'message' => $errorMessage);
}

if (!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
    $encoded = json_encode($responseArray);

    header('Content-Type: application/json');

    echo $encoded;
}
else {
    echo $responseArray['message'];
}

Excellent contact form, works very well. Thank you!
I would like to know how to send an attachment file to the email.
Would it be too complicated to implement on the form?