"Logging in..."
"Some input fields are empty"
"Your username is required"
"Your password is required"

<script type='text/javascript'>
    $(document).ready(function () {

    var submitButton = $("#btn-login");


    submitButton.on('click', function (e) {
        e.preventDefault();

        // Get input field values of the contact form
        var loginFormInputs = $('#login-form :input'),
            userName = $('#txt_uname_email').val(),
            userPassword = $('#txt_password').val(),
            token = $('#token').val(),
            alertMessage = $('#login-alert-message');

        // Disable Inputs and display a loading message
        alertMessage.html('<p style="opacity: 1"><i class="fa fa-spinner fa-spin text-success"></i> Logging in..</p>');
        submitButton.html('<i class="fas fa-spinner fa-spin"></i>');
        loginFormInputs.prop("disabled", true);

        // Data to be sent to server
        var post_data = {
            'form': 'loginForm',
            'userName': userName,
            'userPassword': userPassword,
            'token': token
        };

        // Ajax post data to server
        $.post('./api', post_data, function (response) {


            // Load jsn data from server and output message
            if (response.type === 'error') {

                alertMessage.html('<p><i class="fa-lg far fa-times-circle text-danger"></i> ' + response.text + '</p>');
                submitButton.html('Login');
                loginFormInputs.prop("disabled", false);

            } else {

                alertMessage.html('<p><i class="fa-lg far fa-check-circle text-success"></i> ' + response.text + '</p>');
                submitButton.html('Login');
                window.location = "dashboard";

            }

        }, 'json');

    });

});
</script>

public function doLogin($uname,$umail,$upass)
{
    try
    {
        $stmt = $this->conn->prepare("SELECT * FROM `settings` LIMIT 1");
        $stmt->execute();
        $mainten=$stmt->fetch(PDO::FETCH_ASSOC);
        $stmt = $this->conn->prepare("SELECT user_id, user_name, user_email, user_pass, status FROM users WHERE user_name=:uname OR user_email=:umail ");
        $stmt->execute(array(':uname'=>$uname, ':umail'=>$umail));
        $userRow=$stmt->fetch(PDO::FETCH_ASSOC);
        if($stmt->rowCount() == 1)
        {
            if(password_verify($upass, $userRow['user_pass']))
            {
                session_regenerate_id(false);
                return ["correctPass"=>true, "banned"=> ($userRow['status']== 1) ? true : false, "maintenance"=> ($mainten["maintenance"]== 1) ? true : false];

            }
            else
            {
                return ["correctPass"=>false];
            }
        }
    }
    catch(PDOException $e)
    {
        echo $e->getMessage();
    }
}

require_once("includes/app/class.user.php");
$login = new USER();

    $uname = htmlspecialchars($_POST['userName']);
    $umail = htmlspecialchars($_POST['userName']);
    $upass = htmlspecialchars($_POST['userPassword']);
    $token = $_POST['token'];

if( $_POST && $_POST["form"] === 'loginForm' ) {



    // Use PHP To Detect An Ajax Request
    if( !isset($_SERVER['HTTP_X_REQUESTED_WITH']) AND strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest' ) {

        // Exit script for the JSON data
        $output = json_encode(
            array(
                'type' => 'error',
                'text' => 'Request must come from Ajax'
            ));

        die($output);
    }

    // Checking if the $_POST vars well provided, Exit if there is one missing
    if( !isset($_POST["userName"]) || !isset($_POST["userPassword"]) || !isset($_POST["token"]) ) {

        $output = json_encode(
            array(
                'type' => 'error',
                'text' => 'Some input fields are empty!'
            ));

        die($output);
    }

    // PHP validation for the fields required
    if( empty($_POST["userName"]) ) {
        $output = json_encode(
            array(
                'type' => 'error',
                'text' => 'Your username is required.'
            ));
        die($output);
    }

    if( empty($_POST["userPassword"]) ) {
        $output = json_encode(
            array(
                'type' => 'error',
                'text' => 'Your password is required.'
            ));
        die($output);
    }

    $validation = $login->doLogin($uname,$umail,$upass);
    if($validation["correctPass"]){
        if($validation["maintenance"]){
            if (!in_array($uname, array('admin'))){
                $output = json_encode(
                    array(
                        'type' => 'error',
                        'text' => 'Website under maintenance.'
                    ));
                die($output);
            }
        }
        if($validation["banned"]){
            $output = json_encode(
                array(
                    'type' => 'error',
                    'text' => 'User has been banned.'
                ));
            die($output);
        }else{
            if(Token::check($_POST['token'])) {
            $stmtt = $login->runQuery("SELECT user_id FROM users WHERE user_name=:uname OR user_email=:umail ");
            $stmtt->execute(array(':uname'=>$uname, ':umail'=>$umail));
            $userRow=$stmtt->fetch(PDO::FETCH_ASSOC);
            $_SESSION['user_session'] = $userRow['user_id'];
                  $output = json_encode(
            array(
                'type' => 'message',
                'text' => 'Logged in successfully.'
            ));

            die($output);
            //$success = "Logged in successfully, redirecting..";
            //header( "refresh:3;url=ab" );
            //$login->redirect('dashboard');
            } else {
                $output = json_encode(
                    array(
                        'type' => 'error',
                        'text' => 'Unexpected error occured.'
                    ));
                die($output);
            }
        }
    }
    else{
        $output = json_encode(
            array(
                'type' => 'error',
                'text' => 'Incorrect username or password.'
            ));
        die($output);
    }

}