<?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
 * @link      http://www.gnu.org/software/social/
 */

defined('GNUSOCIAL') || die();

/**
 * ActivityPub's own Explorer
 *
 * Allows to discovery new (or the same) Profiles (both local or remote)
 *
 * @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 Activitypub_explorer
{
    private $discovered_actor_profiles = [];

    /**
     * Shortcut function to get a single profile from its URL.
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     * @param string $url
     * @return Profile
     * @throws Exception
     */
    public static function get_profile_from_url($url)
    {
        $discovery = new Activitypub_explorer;
        // Get valid Actor object
        $actor_profile = $discovery->lookup($url);
        if (!empty($actor_profile)) {
            return $actor_profile[0];
        }
        throw new Exception('Invalid Actor.');
    }

    /**
     * Get every profile from the given URL
     * This function cleans the $this->discovered_actor_profiles array
     * so that there is no erroneous data
     *
     * @param string $url User's url
     * @param bool $remote remote lookup?
     * @return array of Profile objects
     * @throws HTTP_Request2_Exception
     * @throws NoProfileException
     * @throws ServerException
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    public function lookup(string $url, bool $remote = true)
    {
        if (in_array($url, ACTIVITYPUB_PUBLIC_TO)) {
            return [];
        }

        common_debug('ActivityPub Explorer: Started now looking for '.$url);
        $this->discovered_actor_profiles = [];

        return $this->_lookup($url, $remote);
    }

    /**
     * Get every profile from the given URL
     * This is a recursive function that will accumulate the results on
     * $discovered_actor_profiles array
     *
     * @param string $url User's url
     * @param bool $remote remote lookup?
     * @return array of Profile objects
     * @throws HTTP_Request2_Exception
     * @throws NoProfileException
     * @throws ServerException
     * @throws Exception
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    private function _lookup(string $url, bool $remote)
    {
        $grab_local = $this->grab_local_user($url);

        // First check if we already have it locally and, if so, return it.
        // If the local fetch fails and remote grab is required: store locally and return.
        if (!$grab_local && (!$remote || !$this->grab_remote_user($url))) {
            throw new Exception('User not found.');
        }

        return $this->discovered_actor_profiles;
    }

    /**
     * This ensures that we are using a valid ActivityPub URI
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     * @param string $url
     * @return boolean success state (related to the response)
     * @throws Exception (If the HTTP request fails)
     */
    private function ensure_proper_remote_uri($url)
    {
        $client    = new HTTPClient();
        $headers   = [];
        $headers[] = 'Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
        $headers[] = 'User-Agent: GNUSocialBot v0.1 - https://gnu.io/social';
        $response  = $client->get($url, $headers);
        $res = json_decode($response->getBody(), true);
        if (self::validate_remote_response($res)) {
            $this->temp_res = $res;
            return true;
        } else {
            common_debug('ActivityPub Explorer: Invalid potential remote actor while ensuring URI: '.$url. '. He returned the following: '.json_encode($res, JSON_UNESCAPED_SLASHES));
        }

        return false;
    }

    /**
     * Get a local user profile from its URL and joins it on
     * $this->discovered_actor_profiles
     *
     * @param string $uri Actor's uri
     * @param bool $online
     * @return boolean success state
     * @throws NoProfileException
     * @throws Exception
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    private function grab_local_user($uri, $online = false)
    {
        if ($online) {
            common_debug('ActivityPub Explorer: Searching locally for '.$uri. ' with online resources.');
        } else {
            common_debug('ActivityPub Explorer: Searching locally for '.$uri. ' offline.');
        }
        // Ensure proper remote URI
        // If an exception occurs here it's better to just leave everything
        // break than to continue processing
        if ($online && $this->ensure_proper_remote_uri($uri)) {
            $uri = $this->temp_res["id"];
        }

        // Try standard ActivityPub route
        // Is this a known filthy little mudblood?
        $aprofile = self::get_aprofile_by_url($uri);
        if ($aprofile instanceof Activitypub_profile) {
            $profile = $aprofile->local_profile();
            common_debug('ActivityPub Explorer: Found a local Aprofile for '.$uri);
            // We found something!
            $this->discovered_actor_profiles[]= $profile;
            unset($this->temp_res); // IMPORTANT to avoid _dangerous_ noise in the Explorer system
            return true;
        } else {
            common_debug('ActivityPub Explorer: Unable to find a local Aprofile for '.$uri.' - looking for a Profile instead.');
            // Well, maybe it is a pure blood?
            // Iff, we are in the same instance:
            $ACTIVITYPUB_BASE_ACTOR_URI_length = strlen(ACTIVITYPUB_BASE_ACTOR_URI);
            if (substr($uri, 0, $ACTIVITYPUB_BASE_ACTOR_URI_length) == ACTIVITYPUB_BASE_ACTOR_URI) {
                try {
                    $profile = Profile::getByID(intval(substr($uri, $ACTIVITYPUB_BASE_ACTOR_URI_length)));
                    common_debug('ActivityPub Explorer: Found a Profile for '.$uri);
                    // We found something!
                    $this->discovered_actor_profiles[]= $profile;
                    unset($this->temp_res); // IMPORTANT to avoid _dangerous_ noise in the Explorer system
                    return true;
                } catch (Exception $e) {
                    // Let the exception go on its merry way.
                    common_debug('ActivityPub Explorer: Unable to find a Profile for '.$uri);
                }
            }
        }

        // If offline grabbing failed, attempt again with online resources
        if (!$online) {
            common_debug('ActivityPub Explorer: Will try everything again with online resources against: '.$uri);
            return $this->grab_local_user($uri, true);
        }

        return false;
    }

    /**
     * Get a remote user(s) profile(s) from its URL and joins it on
     * $this->discovered_actor_profiles
     *
     * @param string $url User's url
     * @return boolean success state
     * @throws HTTP_Request2_Exception
     * @throws NoProfileException
     * @throws ServerException
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    private function grab_remote_user($url)
    {
        common_debug('ActivityPub Explorer: Trying to grab a remote actor for '.$url);
        if (!isset($this->temp_res)) {
            $client    = new HTTPClient();
            $headers   = [];
            $headers[] = 'Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
            $headers[] = 'User-Agent: GNUSocialBot v0.1 - https://gnu.io/social';
            $response  = $client->get($url, $headers);
            $res = json_decode($response->getBody(), true);
        } else {
            $res = $this->temp_res;
            unset($this->temp_res);
        }
        if (isset($res['type']) && $res['type'] === 'OrderedCollection' && isset($res['first'])) { // It's a potential collection of actors!!!
            common_debug('ActivityPub Explorer: Found a collection of actors for '.$url);
            $this->travel_collection($res['first']);
            return true;
        } elseif (self::validate_remote_response($res)) {
            common_debug('ActivityPub Explorer: Found a valid remote actor for '.$url);
            $this->discovered_actor_profiles[]= $this->store_profile($res);
            return true;
        } else {
            common_debug('ActivityPub Explorer: Invalid potential remote actor while grabbing remotely: '.$url. '. He returned the following: '.json_encode($res, JSON_UNESCAPED_SLASHES));
        }

        // TODO: Fallback to OStatus
        return false;
    }

    /**
     * Save remote user profile in local instance
     *
     * @param array $res remote response
     * @return Profile remote Profile object
     * @throws NoProfileException
     * @throws ServerException
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    private function store_profile($res)
    {
        // ActivityPub Profile
        $aprofile                 = new Activitypub_profile;
        $aprofile->uri            = $res['id'];
        $aprofile->nickname       = $res['preferredUsername'];
        $aprofile->fullname       = isset($res['name']) ? $res['name'] : null;
        $aprofile->bio            = isset($res['summary']) ? substr(strip_tags($res['summary']), 0, 1000) : null;
        $aprofile->inboxuri       = $res['inbox'];
        $aprofile->sharedInboxuri = isset($res['endpoints']['sharedInbox']) ? $res['endpoints']['sharedInbox'] : $res['inbox'];

        $aprofile->do_insert();
        $profile = $aprofile->local_profile();

        // Public Key
        $apRSA = new Activitypub_rsa();
        $apRSA->profile_id = $profile->getID();
        $apRSA->public_key = $res['publicKey']['publicKeyPem'];
        $apRSA->store_keys();

        // Avatar
        if (isset($res['icon']['url'])) {
            try {
                $this->update_avatar($profile, $res['icon']['url']);
            } catch (Exception $e) {
                // Let the exception go, it isn't a serious issue
                common_debug('ActivityPub Explorer: An error ocurred while grabbing remote avatar: '.$e->getMessage());
            }
        }

        return $profile;
    }

    /**
     * Download and update given avatar image
     *
     * @author GNU social
     * @param  Profile $profile
     * @param  string $url
     * @return Avatar    The Avatar we have on disk.
     * @throws Exception in various failure cases
     */
    public static function update_avatar(Profile $profile, $url)
    {
        common_debug('ActivityPub Explorer: Started grabbing remote avatar from: '.$url);
        if (!filter_var($url, FILTER_VALIDATE_URL)) {
            // TRANS: Server exception. %s is a URL.
            common_debug('ActivityPub Explorer: Failed because it is an invalid url: '.$url);
            throw new ServerException(sprintf('Invalid avatar URL %s.', $url));
        }

        // @todo FIXME: This should be better encapsulated
        // ripped from oauthstore.php (for old OMB client)
        $temp_filename = tempnam(sys_get_temp_dir(), 'listener_avatar');
        try {
            $imgData = HTTPClient::quickGet($url);
            // Make sure it's at least an image file. ImageFile can do the rest.
            if (false === getimagesizefromstring($imgData)) {
                common_debug('ActivityPub Explorer: Failed because the downloaded avatar: '.$url. 'is not a valid image.');
                throw new UnsupportedMediaException('Downloaded avatar was not an image.');
            }
            file_put_contents($temp_filename, $imgData);
            unset($imgData);    // No need to carry this in memory.
            common_debug('ActivityPub Explorer: Stored dowloaded avatar in: '.$temp_filename);

            $id = $profile->getID();

            $imagefile = new ImageFile(null, $temp_filename);
            $filename = Avatar::filename(
                $id,
                image_type_to_extension($imagefile->type),
                null,
                common_timestamp()
            );
            rename($temp_filename, Avatar::path($filename));
            common_debug('ActivityPub Explorer: Moved avatar from: '.$temp_filename.' to '.$filename);
        } catch (Exception $e) {
            common_debug('ActivityPub Explorer: Something went wrong while processing the avatar from: '.$url.' details: '.$e->getMessage());
            unlink($temp_filename);
            throw $e;
        }
        // @todo FIXME: Hardcoded chmod is lame, but seems to be necessary to
        // keep from accidentally saving images from command-line (queues)
        // that can't be read from web server, which causes hard-to-notice
        // problems later on:
        //
        // http://status.net/open-source/issues/2663
        chmod(Avatar::path($filename), 0644);

        $profile->setOriginal($filename);

        $orig = clone($profile);
        $profile->avatar = $url;
        $profile->update($orig);

        common_debug('ActivityPub Explorer: Seted Avatar from: '.$url.' to profile.');
        return Avatar::getUploaded($profile);
    }

    /**
     * Validates a remote response in order to determine whether this
     * response is a valid profile or not
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     * @param array $res remote response
     * @return boolean success state
     */
    public static function validate_remote_response($res)
    {
        if (!isset($res['id'], $res['preferredUsername'], $res['inbox'], $res['publicKey']['publicKeyPem'])) {
            return false;
        }

        return true;
    }

    /**
     * Get a ActivityPub Profile from it's uri
     * Unfortunately GNU social cache is not truly reliable when handling
     * potential ActivityPub remote profiles, as so it is important to use
     * this hacky workaround (at least for now)
     *
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     * @param string $v URL
     * @return boolean|Activitypub_profile false if fails | Aprofile object if successful
     */
    public static function get_aprofile_by_url($v)
    {
        $i = Managed_DataObject::getcached("Activitypub_profile", "uri", $v);
        if (empty($i)) { // false = cache miss
            $i = new Activitypub_profile;
            $result = $i->get("uri", $v);
            if ($result) {
                // Hit!
                $i->encache();
            } else {
                return false;
            }
        }
        return $i;
    }

    /**
     * Given a valid actor profile url returns its inboxes
     *
     * @param string $url of Actor profile
     * @return boolean|array false if fails | array with inbox and shared inbox if successful
     * @throws HTTP_Request2_Exception
     * @throws Exception
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    public static function get_actor_inboxes_uri($url)
    {
        $client    = new HTTPClient();
        $headers   = [];
        $headers[] = 'Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
        $headers[] = 'User-Agent: GNUSocialBot ' . GNUSOCIAL_VERSION . ' - https://gnu.io/social';
        $response  = $client->get($url, $headers);
        if (!$response->isOk()) {
            throw new Exception('Invalid Actor URL.');
        }
        $res = json_decode($response->getBody(), true);
        if (self::validate_remote_response($res)) {
            return [
                'inbox' => $res['inbox'],
                'sharedInbox' => isset($res['endpoints']['sharedInbox']) ? $res['endpoints']['sharedInbox'] : $res['inbox']
            ];
        }

        return false;
    }

    /**
     * Allows the Explorer to transverse a collection of persons.
     *
     * @param string $url
     * @return boolean
     * @throws HTTP_Request2_Exception
     * @throws NoProfileException
     * @throws ServerException
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    private function travel_collection($url)
    {
        $client    = new HTTPClient();
        $headers   = [];
        $headers[] = 'Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
        $headers[] = 'User-Agent: GNUSocialBot v0.1 - https://gnu.io/social';
        $response  = $client->get($url, $headers);
        $res = json_decode($response->getBody(), true);

        if (!isset($res['orderedItems'])) {
            return false;
        }

        foreach ($res["orderedItems"] as $profile) {
            if ($this->_lookup($profile) == false) {
                common_debug('ActivityPub Explorer: Found an invalid actor for '.$profile);
                // TODO: Invalid actor found, fallback to OStatus
            }
        }
        // Go through entire collection
        if (!is_null($res["next"])) {
            $this->_lookup($res["next"]);
        }

        return true;
    }

    /**
     * Get a remote user array from its URL (this function is only used for
     * profile updating and shall not be used for anything else)
     *
     * @param string $url User's url
     * @return mixed
     * @throws Exception
     * @author Diogo Cordeiro <diogo@fc.up.pt>
     */
    public static function get_remote_user_activity($url)
    {
        $client    = new HTTPClient();
        $headers   = [];
        $headers[] = 'Accept: application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
        $headers[] = 'User-Agent: GNUSocialBot v0.1 - https://gnu.io/social';
        $response  = $client->get($url, $headers);
        $res = json_decode($response->getBody(), true);
        if (Activitypub_explorer::validate_remote_response($res)) {
            common_debug('ActivityPub Explorer: Found a valid remote actor for '.$url);
            return $res;
        }
        throw new Exception('ActivityPub Explorer: Failed to get activity.');
    }
}