signup form

<?php
include('header.php');

if(isset($_POST['user_signup'])) {

$username = mysqli_real_escape_string($conn, $_POST['username']);
$email = mysqli_real_escape_string($conn, $_POST['email']);
$get_ip = get_user_ip();

$check_username = mysqli_query($conn, "SELECT username FROM `users` WHERE `username`='".$username."'");
$username_exists = mysqli_num_rows($check_username);

$check_email = mysqli_query($conn, "SELECT email FROM `users` WHERE `email`='".$email."'");
$email_exists = mysqli_num_rows($check_email);

$check_ip = mysqli_query($conn, "SELECT ip FROM `users` WHERE `ip`='".$get_ip."'");
$ip_exists = mysqli_num_rows($check_ip);

if($username_exists == 1) {
$message = "<div class=\"alert alert-danger\">That username is not available.</div>";
} else if($email_exists == 1) {
$message = "<div class=\"alert alert-danger\">That email is already registered.</div>";
} else if($ip_exists == 1) {
$message = "<div class=\"alert alert-danger\">That ip is already registered to an account, you can only have  1 account.</div>";
} else if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
$message = "<div class=\"alert alert-danger\">Invalid email format. Valid: <i>admin@example.com</i></div>";
} else if(!preg_match("/^[a-z0-9]+$/i", $_POST['username'])) {
$message = "<div class=\"alert alert-danger\">Username must contain only letters and numbers.</div>";
} else if(empty($_POST['email']) || $_POST['email'] == "") {
$message = "<div class=\"alert alert-danger\">Email is empty, try again.</div>";
} else if(empty($_POST['username']) || $_POST['username'] == "") {
$message = "<div class=\"alert alert-danger\">Username is empty, try again.</div>";
} else if(empty($_POST['password']) || $_POST['password'] == "") {
$message = "<div class=\"alert alert-danger\">Password is empty, try again.</div>";
} else if(strlen($_POST['username']) > 20) {
$message = "<div class=\"alert alert-danger\">Username must be shorter than 20 characters.</div>";
} else if(strlen($_POST['username']) < 6) {
$message = "<div class=\"alert alert-danger\">Username must be greater than 5 characters.</div>";
} else {

$username = mysqli_real_escape_string($conn, $_POST['username']);
$email = mysqli_real_escape_string($conn, $_POST['email']);
$password = md5($_POST['password']);
$ip = get_user_ip();

$ref_id = "";
if(isset($_COOKIE['user_referral'])) {
$username = mysqli_real_escape_string($conn, $_POST['username']);
$ref_ip = get_user_ip();
$ref_id = $_COOKIE['user_referral'];
$referral_sql = mysqli_query($conn, "SELECT * FROM `users` WHERE `user_id`='{$ref_id}'");
$referral = mysqli_fetch_array($referral_sql, MYSQLI_ASSOC);

mysqli_query($conn, "INSERT INTO `users_referrals`(referral_username,referral_referral,referral_ip,referral_date_added) values('{$referral['username']}','{$username}','{$ref_ip}',NOW())");
}

if($config['site_signup_bonus'] > 0) {
$signup_point_bonus = $config['site_signup_bonus'];
} else {
$signup_point_bonus = 0;
}

mysqli_query($conn, "INSERT INTO `users`(email,username,ip,password,signup,online,points,referral) values('{$email}','{$username}','{$ip}','{$password}',NOW(),NOW(),'{$signup_point_bonus}','{$ref_id}')");

$_SESSION['username'] = $username;
echo "<script>document.location.href='".$config['site_url']."dashboard'</script>";

}
}

?>

<div class="container">

<div class="row row-centered">
<div class="col-lg-5 col-centered">
<?php if(!isset($user)): ?>
      <form class="form-signin" role="form" method="post" action="signup.php">
        <h2 class="form-signin-heading">GiftCardsSky : Signup</h2>

<?php if(isset($message)) echo $message; ?>

<div class="form-group">
        <label for="inputEmail" class="sr-only">Username</label>
        <input type="email" name="email" id="email" class="form-control" placeholder="Email" required autofocus>
        </div>

<div class="form-group">
        <label for="inputEmail" class="sr-only">Username</label>
        <input type="text" name="username" id="inputUsername" class="form-control" placeholder="Username" required autofocus>
        </div>

        <div class="form-group">
        <label for="inputPassword" class="sr-only">Password</label>
        <input type="password" name="password" id="inputPassword" class="form-control" placeholder="Password" required>
        </div>
<div class="form-group">
        <button class="btn btn-lg btn-primary btn-block" name="user_signup" type="submit">Sign up</button>
        </div>
      </form>
<?php else: ?>
<div class="alert alert-dismissable alert-danger">
  <button type="button" class="close" data-dismiss="alert">Ч</button>
  <strong>Oh.. </strong> You're already logged in <?php echo $user['username']; ?>!
</div>
<?php endif; ?>

    </div>
    </div>
    </div> <!-- /container -->


<?php include('footer.php'); ?>