PHP script for contact form

contact-form.css

.contact-form input:not(:placeholder-shown):valid,
.contact-form textarea:not(:placeholder-shown):valid {
  background-color: #f4feee;
}

.contact-form input:not(:placeholder-shown):invalid,
.contact-form textarea:not(:placeholder-shown):invalid {
  background-color: #fff0f0;
}

.contact-form label,
.contact-form button {
  display: block;
}

.js-submitted input:valid,
.js-submitted textarea:valid {
  background-color: #f4feee;
}

.js-submitted input:invalid,
.js-submitted textarea:invalid {
  background-color: #fff0f0;
}

.hidden {
  display: none;
}

contact-form.js

(function ($) {
  ("use strict");

  // Remove the "no javascript" messages
  $(".contact-no-js").detach();

  // Contact form.
  $(".contact-form").each(function () {
    var $contact_form = $(this);
    var $contact_button = $contact_form.find(".form-submit");
    var contact_action = "/assets/php/contact.php";

    // Display the hidden form.
    $contact_form.removeClass("hidden");

    // Wait for a mouse to move, indicating they are human.
    $("body").mousemove(function () {
      // Unlock the form.
      $contact_form.attr("action", contact_action);
      $contact_button.attr("disabled", false);
    });

    // Wait for a touch move event, indicating that they are human.
    $("body").on("touchmove", function () {
      // Unlock the form.
      $contact_form.attr("action", contact_action);
      $contact_button.attr("disabled", false);
    });

    // A tab or enter key pressed can also indicate they are human.
    $("body").keydown(function (e) {
      if (e.keyCode === 9 || e.keyCode === 13) {
        // Unlock the form.
        $contact_form.attr("action", contact_action);
        $contact_button.attr("disabled", false);
      }
    });

    // Mark the form as submitted.
    $contact_button.click(function () {
      $contact_form.addClass("js-submitted");
    });

    // Display messages.
    if (location.search.substring(1) !== "") {
      switch (location.search.substring(1)) {
        case "submitted":
          $(".contact-submitted").removeClass("hidden");
          break;

        case "error":
          $(".contact-error").removeClass("hidden");
          break;
      }
    }
  });
})(jQuery);

contact.html

<p class="contact-no-js messages messages--error">You must have Javascript enabled to use this contact form.</p>
<p class="contact-submitted messages messages--status hidden">Your message was sent.</p>
<p class="contact-error messages messages--error hidden">There was an error sending the message.</p>

<form class="contact-form hidden" action="#" method="post" accept-charset="UTF-8">
  <div class="form-item">
    <label for="edit-name">
      Your Name
      <span class="form-required" title="This field is required.">*</span>
    </label>
    <input type="text" id="edit-name" name="name" placeholder="Your name" tabindex="1" required autofocus>
  </div>
  <div class="form-item">
    <label for="edit-mail">
      Your e-mail address
      <span class="form-required" title="This field is required.">*</span>
    </label>
    <input type="email" class="form-text" id="edit-mail" name="email" placeholder="Your e-mail address" tabindex="2" required>
  </div>
  <div class="form-item">
    <input type="text" id="edit-url" class="hidden" name="url" placeholder="Skip if you are a human">
  </div>
  <div class="form-item">
    <label for="edit-name">
      Telephone
      <span class="form-required" title="This field is required.">*</span>
    </label>
    <input type="text" id="edit-phone" name="phone" placeholder="Your phone" tabindex="3" required>
  </div>
  <div class="form-item">
    <label for="edit-message">
      Message
      <span class="form-required" title="This field is required.">*</span>
    </label>
    <textarea id="edit-message" name="message" rows="5" placeholder="Please tell us about your travel dates and how many people are traveling." tabindex="5" required></textarea>
  </div>
  <div class="form-actions">
    <button type="submit" name="submit" class="form-submit" disabled>Send message</button>
  </div>
</form>

contact.php

<?php
/**
 * Working spam-free php email script for Dreamhost.
 * https://gist.github.com/jameswilson/3fbb21c0669de2c7a29720e6d7aa88c7
 * Adapted from https://gist.github.com/frjo/23e45ec5e690d90f6bfcaca06873fd73
 * https://codepen.io/frjo/pen/pwWoEd/
 * https://xdeb.org/post/2017/a-html5-php-javascript-contact-form-with-spam-protection/
 */

// Set the e-mail address that submission should be sent to.
$to = 'info@example.com';

// Optionally, add a blind carbon copy, set to false or empty string to disable.
$bcc = 'another@example.com';

// Set the sender/return path header to your Dreamhost server account to avoid
// sending errors.
$sender = 'Example.com <useraccount@servername.dreamhost.com>';

// Set the e-mail subject prefix.
$prefix = 'Website feedback';

// DO NOT EDIT ANYTHING BELOW UNLESS YOU KNOW WHAT YOU ARE DOING.

$error = false;
$success = false;

// Check that referer is local server.
if (!isset($_SERVER['HTTP_REFERER']) || (parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST) != $_SERVER['SERVER_NAME'])) {
  exit('Direct access not permitted');
}

// Get the URL that submitted the form.
$contact_form_url = strtok($_SERVER['HTTP_REFERER'], '?');

// Check that this is a post request.
if ($_SERVER['REQUEST_METHOD'] != 'POST' || empty($_POST)) {
  $error = true;
}

// Check if fake url field is filled in, i.e. spam bot.
if (!empty($_POST['url'])) {
  $error = true;
}

// Check that e-mail address is valid.
if ((bool) filter_var(trim($_POST['email']), FILTER_VALIDATE_EMAIL)) {
  $email = trim($_POST['email']);
} else {
  $error = true;
}

if (!$error) {
  // Construct the mail with headers.
  $name = _contact_clean_str($_POST['name'], ENT_QUOTES, true, true);
  $prefix = _contact_clean_str($prefix, ENT_NOQUOTES, true, true);
  $phone = _contact_clean_str($_POST['phone'], ENT_NOQUOTES, true, true);
  $subject = "[$prefix] Message from $name";
  $message = _contact_clean_str($_POST['message'], ENT_NOQUOTES);
  $lines = explode("\n", $message);
  array_walk($lines, '_contact_ff_wrap');
  $message = "Dear admin, $name sent you the following message:\n\n-----\n\n";
  $message .= implode("\n", $lines) . "\n\n-----\n\n";
  $message .= "Email: $email\n";
  $message .= "Phone: $phone\n";
  $message .= "Submitted via: $contact_form_url\n";
  $headers = [
    'From'                      => $sender,
    'Sender'                    => $sender,
    'Return-Path'               => $sender,
    'Reply-To'                  => "$name <$email>",
    'MIME-Version'              => '1.0',
    'Content-Type'              => 'text/plain; charset=UTF-8; format=flowed; delsp=yes',
    'Content-Transfer-Encoding' => '8Bit',
    'X-Mailer'                  => 'PHP Mail',
  ];
  if ($bcc) {
    $headers["Bcc"] = $bcc;
  }
  $mime_headers = [];
  foreach ($headers as $key => $value) {
    $mime_headers[] = "$key: $value";
  }
  $mail_headers = join("\n", $mime_headers);

  // Send the mail, suppressing errors and setting Return-Path with the "-f" option.
  $success = @mail($to, $subject, $message, $mail_headers, '-f' . $sender);
}

$status = $success ? 'submitted' : 'error';

// Redirect back to contact form with status.
header('Location: ' . $contact_form_url . '?' . $status, TRUE, 302);
exit;

function _contact_ff_wrap(&$line) {
  $line = wordwrap($line, 72, " \n");
}

function _contact_clean_str($str, $quotes, $strip = false, $encode = false) {
  if ($strip) {
    $str = strip_tags($str);
  }

  $str = htmlspecialchars(trim($str), $quotes, 'UTF-8');

  if ($encode && preg_match('/[^\x20-\x7E]/', $str)) {
    $str = '=?UTF-8?B?' . base64_encode($str) . '?=';
  }

  return $str;
}