OnlineUsers.php

<?php
//http://flask.pocoo.org/snippets/71/ that is good idea
include 'predis/predis.phar';

class OnlineUsers {

    /* time to consider user online */
    private $minutes = 5 ;

    function online() {
        /* current hour and minute */
        $now = time();
        $min = date("i",$now);
        $hor = date("G",$now);

        /* redis keys to union, based on last $minutes */
        $keys = array();
        for($i = $min ; $i >= $min - $this->minutes; $i--) {
            $keys[] = "online:".$hor.":".$i; // define the key
        }

        $redis = new Predis\Client(); // connect to redis at localhost
        $scmd = $redis->createCommand("sunion",$keys); // create the union with desired keys
        $online = $redis->executeCommand($scmd); // issue the sunion and grab the result
        
        return $online ; // array of online usernames
    }

    function ping($user) {
        /* current hour:minute to make up the redis key */
        $now  = time();
        $min  = date("G:i",$now);
        $key  = "online:".$min;

        $redis = new Predis\Client(); // connect to redis at localhost

        $redis->sadd($key,$user); // add the user to the set
        $ttl = $redis->ttl($key) ; // check if key has an expire
        if($ttl == -1) { // if it do not have, set it to $minutes + 1
            $redis->expire($key, ($minutes + 1) * 60);
        }
        
        return $this ;
    }
}

?>