1<?php
2// This file is part of Moodle - http://moodle.org/
3//
4// Moodle is free software: you can redistribute it and/or modify
5// it under the terms of the GNU General Public License as published by
6// the Free Software Foundation, either version 3 of the License, or
7// (at your option) any later version.
8//
9// Moodle is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12// GNU General Public License for more details.
13//
14// You should have received a copy of the GNU General Public License
15// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
16
17/**
18 * Cache data source for the time of the last message between users.
19 *
20 * @package    core_message
21 * @category   cache
22 * @copyright  2016 Ryan Wyllie <ryan@moodle.com>
23 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
24 */
25
26namespace core_message;
27
28defined('MOODLE_INTERNAL') || die();
29
30/**
31 * Cache data source for the time of the last message in a conversation.
32 *
33 * @package    core_message
34 * @category   cache
35 * @copyright  2016 Ryan Wyllie <ryan@moodle.com>
36 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
37 */
38class time_last_message_between_users implements \cache_data_source {
39
40    /** @var time_last_message_between_users the singleton instance of this class. */
41    protected static $instance = null;
42
43    /**
44     * Returns an instance of the data source class that the cache can use for loading data using the other methods
45     * specified by the cache_data_source interface.
46     *
47     * @param \cache_definition $definition
48     * @return object
49     */
50    public static function get_instance_for_cache(\cache_definition $definition) {
51        if (is_null(self::$instance)) {
52            self::$instance = new time_last_message_between_users();
53        }
54        return self::$instance;
55    }
56
57    /**
58     * Loads the data for the key provided ready formatted for caching.
59     *
60     * @param string|int $key The key to load.
61     * @return mixed What ever data should be returned, or false if it can't be loaded.
62     */
63    public function load_for_cache($key) {
64        $message = api::get_most_recent_conversation_message($key);
65
66        if ($message) {
67            return $message->timecreated;
68        } else {
69            return null;
70        }
71    }
72
73    /**
74     * Loads several keys for the cache.
75     *
76     * @param array $keys An array of keys each of which will be string|int.
77     * @return array An array of matching data items.
78     */
79    public function load_many_for_cache(array $keys) {
80        $results = [];
81
82        foreach ($keys as $key) {
83            $results[] = $this->load_for_cache($key);
84        }
85
86        return $results;
87    }
88}
89