<?php
// This file is part of GNU social - https://www.gnu.org/software/social
//
// GNU social is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// GNU social is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with GNU social.  If not, see <http://www.gnu.org/licenses/>.

/**
 * ActivityPub implementation for GNU social
 *
 * @package   GNUsocial
 *
 * @author    Diogo Cordeiro <diogo@fc.up.pt>
 * @copyright 2018-2019 Free Software Foundation, Inc http://www.fsf.org
 * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
 *
 * @see      http://www.gnu.org/software/social/
 */
defined('GNUSOCIAL') || die();

/**
 * Actor's Followers Collection
 *
 * @category  Plugin
 * @package   GNUsocial
 *
 * @author    Diogo Cordeiro <diogo@fc.up.pt>
 * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
 */
class apActorFollowersAction extends ManagedAction
{
    protected $needLogin = false;
    protected $canPost   = true;

    /**
     * Handle the Followers Collection request
     *
     * @throws Exception
     *
     * @return void
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    protected function handle()
    {
        try {
            $profile    = Profile::getByID($this->trimmed('id'));
            $profile_id = $profile->getID();
        } catch (Exception $e) {
            ActivityPubReturn::error('Invalid Actor URI.', 404);
        }

        if (!$profile->isLocal()) {
            ActivityPubReturn::error('This is not a local user.', 403);
        }

        if (!isset($_GET['page'])) {
            $page = 0;
        } else {
            $page = (int) ($this->trimmed('page'));
        }

        if ($page < 0) {
            ActivityPubReturn::error('Invalid page number.');
        }

        $since = ($page - 1) * PROFILES_PER_MINILIST;
        $limit = PROFILES_PER_MINILIST;

        // Calculate total items
        $total_subs  = Activitypub_profile::subscriberCount($profile);
        $total_pages = ceil($total_subs / PROFILES_PER_MINILIST);

        $res = [
            '@context' => [
                'https://www.w3.org/ns/activitystreams',
                'https://w3id.org/security/v1',
            ],
            'id'         => common_local_url('apActorFollowers', ['id' => $profile_id]) . (($page != 0) ? '?page=' . $page : ''),
            'type'       => ($page == 0 ? 'OrderedCollection' : 'OrderedCollectionPage'),
            'totalItems' => $total_subs,
        ];

        if ($page == 0) {
            $res['first'] = common_local_url('apActorFollowers', ['id' => $profile_id]) . '?page=1';
        } else {
            $res['orderedItems'] = $this->generate_followers($profile, $since, $limit);
            $res['partOf']       = common_local_url('apActorFollowers', ['id' => $profile_id]);

            if ($page + 1 < $total_pages) {
                $res['next'] = common_local_url('apActorFollowers', ['id' => $profile_id]) . 'page=' . ($page + 1 == 1 ? 2 : $page + 1);
            }

            if ($page > 1) {
                $res['prev'] = common_local_url('apActorFollowers', ['id' => $profile_id]) . '?page=' . ($page - 1 <= 0 ? 1 : $page - 1);
            }
        }

        ActivityPubReturn::answer($res);
    }

    /**
     * Generates a list of stalkers for a given profile.
     *
     * @param Profile $profile
     * @param int     $since
     * @param int     $limit
     *
     * @throws Exception
     *
     * @return array of URIs
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    public static function generate_followers($profile, $since, $limit)
    {
        $subs = [];
        try {
            $sub = Activitypub_profile::getSubscribers($profile, $since, $limit);

            // Get followers' URLs
            foreach ($sub as $s) {
                $subs[] = $s->getUri();
            }
        } catch (NoResultException $e) {
            // Just let the exception go on its merry way
        }

        return $subs;
    }
}