VK(.com) Bot for the last_seen value

cron.php

<?php
/**
 * VK(.com) Bot for the last_seen value
 *
 * @author Sergej Müller
 */


/**
 * Main class
 */

class LastSeenVKBot {


    /**
      * @var string $vk_api_url VK API URL for user requests
      */
    protected static $vk_api_url = 'http://api.vkontakte.ru/method/users.get';


    /**
      * Prepare API call and user notification
      *
      * @param integer $vk_user_id VK UserID
      * @param integer $last_seen_alert Maximum off-time in seconds before a notification is sent out
      * @param boolean $skip_api_call Break API calls (e.g. timed calls)
      *
      * @return void
      */
    public function __construct($vk_user_id, $last_seen_alert, $skip_api_call) {
        if ( ! empty($skip_api_call) ) {
            return;
        }

        if ( empty($vk_user_id) ) {
            die('Empty $vk_user_id');
        }

        if ( empty($last_seen_alert) ) {
            return;
        }

        $last_seen_time = (int) self::_get_last_seen( $vk_user_id );
        $offline_time = time() - $last_seen_time;

        if ( $offline_time >= $last_seen_alert ) {
            self::_send_user_alert(
                self::_human_time( $offline_time )
            );
        }

        die('Done!');
    }


    /**
      * API Call for the last_seen value binded on UserID
      *
      * @param integer $vk_user_id UserID
      *
      * @return integer Last seen timestamp for UserID
      */
    protected static function _get_last_seen($vk_user_id) {
        if ( ! is_numeric($vk_user_id) ) {
            die('Empty $vk_user_id');
        }

        $content = file_get_contents(
            sprintf(
                '%s?%s',
                self::$vk_api_url,
                http_build_query(
                    array(
                        'uids' => $vk_user_id,
                        'fields' => 'last_seen'
                    )
                )

            )
        );

        if ( empty($content) ) {
            die('Empty $content');
        }

        $json = json_decode($content, true);

        if ( json_last_error() != JSON_ERROR_NONE ) {
            die('Error at $json');
        }

        return $json['response'][0]['last_seen']['time'];
    }


    /**
      * Send a notification
      *
      * @param integer $offline_time Offline time aggregated from VK API
      *
      * @return void
      */
    protected static function _send_user_alert($offline_time) {
        mail(
            'email@email.de',
            'Missing on VK',
            'Last seen: ' .$offline_time. ' ago',
            'From: email@email.de'
        );
    }


    /**
      * Determines the difference between two timestamps in a human readable format.
      *
      * @param integer $time Unix timestamp from which the difference begins
      *
      * @return string Human readable time difference
      */
    protected static function _human_time($time) {
        $time = ( $time < 1 ) ? 1 : $time;

        $tokens = array (
            31536000 => 'year',
            2592000 => 'month',
            604800 => 'week',
            86400 => 'day',
            3600 => 'hour',
            60 => 'minute',
            1 => 'second'
        );

        foreach ($tokens as $unit => $text) {
            if ($time < $unit) continue;
            $numberOfUnits = floor($time / $unit);

            return sprintf(
                '%d %s%s',
                $numberOfUnits,
                $text,
                ( $numberOfUnits > 1 ? 's' : '' )
            );
        }

    }
}


new LastSeenVKBot(
    1234567, // target  user id
    (3 * 60 * 60), // 3 hours
    ( date('G') < 9 OR date('G') > 21 ) // daytime only
);