Using date_parse_from_format on PHP 5.2

Last week, I was working on a problem of the Datepicker formats been really weird on some cases for The Events Calendar plugin, as Modern Tribe does support WordPress minimum PHP required version for it's plugins, the developers have to solve some problems with the Tools that PHP 5.2 provides us.

The enemy! ?

Fatal error: Call to undefined function date_parse_from_format()

On the case of dates, this becomes a real problem since we don't have support for the date_parse_from_format or DateTime::createFromFormat() we needed to be able to parse formats like 15/02/1993 formatted with d/m/Y.

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Display online Users on WordPress

Earlier today I ran into a problem where I needed a simple way to display which registered users are online right now on the site.

I've done a Video explaining what was my solution and how to apply it to a theme, but I myself hate when I see a video without any code that I can easily take a look at, so below the video you will find a explanation of the code step by step, and in the end the plugin I created for this purpose.

Please note that I will comment further the code on the video, but there are some comments on each one of the snippets here

Variables used

We will use only two variables on this plugin:

  • static protected $_instance = null; -- Holds the static instance of our class after the plugin is initialized
  • static protected $prefix = 'OnlineNow'; -- Prefix we will use on the Database Options

Class Instance handling

When dealing with plugins in WordPress a good practice is to save a static variable of the main class on a private/protected variable and create a static method to instantiate the class whenever you call this method the first time:

static public function instance(){
    null === self::$_instance and self::$_instance = new self;
    return self::$_instance;

Plugin Initialization

Here is where our plugin will hook into WordPress and do the required actions to allot this plugin to work as we expect.

static public function init(){
    // Lock this class to be initialized only once
    if ( null !== self::$_instance ){
        return false;
    add_action( 'wp_login', array( self::instance(), 'login' ), 10, 2 );
    add_action( 'clear_auth_cookie', array( self::instance(), 'logout' ), 10 );

    // Register Shortcodes
    add_shortcode( 'online:list', array( self::instance(), 'shortcode_list' ) );
    add_shortcode( 'online:qty', array( self::instance(), 'shortcode_qty' ) );

    add_filter('widget_text', 'do_shortcode');

    return true;

Register when a User logs in

We need to register when a user do the login so that we can save it in the database to grab this value and display for the users.

public function login( $user_login, $user ) {
    $users = get_option( self::$prefix . '-users', array() );

    if ( in_array( $user->ID, $users ) ){

    $users[] = $user->ID;

    update_option( self::$prefix . '-users', $users );

Register when a User logs out

Just like when we register the action of login and add the user ID to the database option, now we will remove that ID when the user logs out.

public function logout() {
    $users = get_option( self::$prefix . '-users', array() );

    $user_id = get_current_user_id();

    if ( ! in_array( $user_id, $users ) ){

    update_option( self::$prefix . '-users', array_diff( $users , array( $user_id ) ) );

Grab the users logged in

We need a method that will allow us to get the users from the database option, I've also allowed the developer to exclude or include a user to the list.

public function get_users( $include = array(), $exclude = array() ){
    // Retrieve the users from Database
    $users = get_option( self::$prefix . '-users', array() );

    // Parse Shortcode atts to exclude
    if ( is_string( $exclude ) ){
        $exclude = array_map( 'trim', explode( ',', $exclude ) );

    // Exclude users based on shortcode attribute
    $users = array_diff( (array) $users, (array) $exclude );

    // Parse Shortcode atts to include
    if ( is_string( $include ) ){
        $include = array_map( 'trim', explode( ',', $include ) );

    // Include users based on shortcode attribute
    $users = array_merge( (array) $users, (array) $include );

    // Garantee that the array is safe for usage
    $users = array_unique( array_filter( (array) $users ) );

    // Remove all non existent users
    $users = array_map( array( $this, 'user_exists' ), $users );

    // Garantee that the array is safe for usage
    $users = array_filter( (array) $users );

    return $users;

Then I used a method inside of the get_users to check if the user exists before return the list of WP_User objects - on video.

public function user_exists( $user_id ){
    $user = new WP_User( $user_id );

    // Check if the users exists
    if ( ! $user->exists() ){
        return false;

    return $user;

List Online Users Shortcode

After we did all the hard work of storing the data about user on the database, now we will use that information to print an HTML with the list of users that are currently online.

public function shortcode_list( $atts ) {
    $atts = (object) shortcode_atts( array(
        'avatar' => false,

        'exclude' => '',
        'include' => '',
    ), $atts );

    $users = $this->get_users( $atts->include, $atts->exclude );

    $html = '<ul class="users-online">';
    foreach ( (array) $users as $user ) {
        $html .= '<li>';
        // Allow the user to control the avatar size and if he wants to show
        if ( is_numeric( $atts->avatar ) ){
            $html .= get_avatar( $user , $atts->avatar );
        $html .= '<span>' . $user->display_name . '</span>';
        $html .= '</li>';
    $html .= '</ul>';
    return $html;

Display the quantity of Users Online

The user might also want to display the quantity of users that are online with a shortcode, so we will deal with that too.

public function shortcode_qty( $atts ) {
    $atts = (object) shortcode_atts( array(
        'plural' => __( '%s users online', 'online-now' ),
        'singular' => __( 'One user online', 'online-now' ),
        'zero' => __( 'Zero users online', 'online-now' ),

        'numeric' => false,

        'exclude' => '',
        'include' => '',
    ), $atts );

    $users = $this->get_users( $atts->include, $atts->exclude );

    if ( $atts->numeric ){
        return count( $users );

    if ( count( $users ) === 0 ) {
        $text = $atts->zero;
    } elseif ( count( $users ) === 1 ) {
        $text = $atts->singular;
    } else {
        $text = $atts->plural;

    return sprintf( $text, count( $users ) );

Repository and Download

You can always checkout the oficial repository for this plugin and/or download the latest version of the code to install it in your WordPress.