/repository/lib.php

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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * This file contains classes used to manage the repository plugins in Moodle
 *
 * @since 2.0
 * @package   core_repository
 * @copyright 2009 Dongsheng Cai {@link http://dongsheng.org}
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();
require_once($CFG->libdir . '/filelib.php');
require_once($CFG->libdir . '/formslib.php');

define('FILE_EXTERNAL',  1);
define('FILE_INTERNAL',  2);
define('FILE_REFERENCE', 4);
define('RENAME_SUFFIX', '_2');

/**
 * This class is used to manage repository plugins
 *
 * A repository_type is a repository plug-in. It can be Box.net, Flick-r, ...
 * A repository type can be edited, sorted and hidden. It is mandatory for an
 * administrator to create a repository type in order to be able to create
 * some instances of this type.
 * Coding note:
 * - a repository_type object is mapped to the "repository" database table
 * - "typename" attibut maps the "type" database field. It is unique.
 * - general "options" for a repository type are saved in the config_plugin table
 * - when you delete a repository, all instances are deleted, and general
 *   options are also deleted from database
 * - When you create a type for a plugin that can't have multiple instances, a
 *   instance is automatically created.
 *
 * @package   core_repository
 * @copyright 2009 Jerome Mouneyrac
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class repository_type implements cacheable_object {


    /**
     * Type name (no whitespace) - A type name is unique
     * Note: for a user-friendly type name see get_readablename()
     * @var String
     */
    private $_typename;


    /**
     * Options of this type
     * They are general options that any instance of this type would share
     * e.g. API key
     * These options are saved in config_plugin table
     * @var array
     */
    private $_options;


    /**
     * Is the repository type visible or hidden
     * If false (hidden): no instances can be created, edited, deleted, showned , used...
     * @var boolean
     */
    private $_visible;


    /**
     * 0 => not ordered, 1 => first position, 2 => second position...
     * A not order type would appear in first position (should never happened)
     * @var integer
     */
    private $_sortorder;

    /**
     * Return if the instance is visible in a context
     *
     * @todo check if the context visibility has been overwritten by the plugin creator
     *       (need to create special functions to be overvwritten in repository class)
     * @param stdClass $context context
     * @return bool
     */
    public function get_contextvisibility($context) {
        global $USER;

        if ($context->contextlevel == CONTEXT_COURSE) {
            return $this->_options['enablecourseinstances'];
        }

        if ($context->contextlevel == CONTEXT_USER) {
            return $this->_options['enableuserinstances'];
        }

        //the context is SITE
        return true;
    }



    /**
     * repository_type constructor
     *
     * @param int $typename
     * @param array $typeoptions
     * @param bool $visible
     * @param int $sortorder (don't really need set, it will be during create() call)
     */
    public function __construct($typename = '', $typeoptions = array(), $visible = true, $sortorder = 0) {
        global $CFG;

        //set type attributs
        $this->_typename = $typename;
        $this->_visible = $visible;
        $this->_sortorder = $sortorder;

        //set options attribut
        $this->_options = array();
        $options = repository::static_function($typename, 'get_type_option_names');
        //check that the type can be setup
        if (!empty($options)) {
            //set the type options
            foreach ($options as $config) {
                if (array_key_exists($config, $typeoptions)) {
                    $this->_options[$config] = $typeoptions[$config];
                }
            }
        }

        //retrieve visibility from option
        if (array_key_exists('enablecourseinstances',$typeoptions)) {
            $this->_options['enablecourseinstances'] = $typeoptions['enablecourseinstances'];
        } else {
             $this->_options['enablecourseinstances'] = 0;
        }

        if (array_key_exists('enableuserinstances',$typeoptions)) {
            $this->_options['enableuserinstances'] = $typeoptions['enableuserinstances'];
        } else {
             $this->_options['enableuserinstances'] = 0;
        }

    }

    /**
     * Get the type name (no whitespace)
     * For a human readable name, use get_readablename()
     *
     * @return string the type name
     */
    public function get_typename() {
        return $this->_typename;
    }

    /**
     * Return a human readable and user-friendly type name
     *
     * @return string user-friendly type name
     */
    public function get_readablename() {
        return get_string('pluginname','repository_'.$this->_typename);
    }

    /**
     * Return general options
     *
     * @return array the general options
     */
    public function get_options() {
        return $this->_options;
    }

    /**
     * Return visibility
     *
     * @return bool
     */
    public function get_visible() {
        return $this->_visible;
    }

    /**
     * Return order / position of display in the file picker
     *
     * @return int
     */
    public function get_sortorder() {
        return $this->_sortorder;
    }

    /**
     * Create a repository type (the type name must not already exist)
     * @param bool $silent throw exception?
     * @return mixed return int if create successfully, return false if
     */
    public function create($silent = false) {
        global $DB;

        //check that $type has been set
        $timmedtype = trim($this->_typename);
        if (empty($timmedtype)) {
            throw new repository_exception('emptytype', 'repository');
        }

        //set sortorder as the last position in the list
        if (!isset($this->_sortorder) || $this->_sortorder == 0 ) {
            $sql = "SELECT MAX(sortorder) FROM {repository}";
            $this->_sortorder = 1 + $DB->get_field_sql($sql);
        }

        //only create a new type if it doesn't already exist
        $existingtype = $DB->get_record('repository', array('type'=>$this->_typename));
        if (!$existingtype) {
            //create the type
            $newtype = new stdClass();
            $newtype->type = $this->_typename;
            $newtype->visible = $this->_visible;
            $newtype->sortorder = $this->_sortorder;
            $plugin_id = $DB->insert_record('repository', $newtype);
            //save the options in DB
            $this->update_options();

            $instanceoptionnames = repository::static_function($this->_typename, 'get_instance_option_names');

            //if the plugin type has no multiple instance (e.g. has no instance option name) so it wont
            //be possible for the administrator to create a instance
            //in this case we need to create an instance
            if (empty($instanceoptionnames)) {
                $instanceoptions = array();
                if (empty($this->_options['pluginname'])) {
                    // when moodle trying to install some repo plugin automatically
                    // this option will be empty, get it from language string when display
                    $instanceoptions['name'] = '';
                } else {
                    // when admin trying to add a plugin manually, he will type a name
                    // for it
                    $instanceoptions['name'] = $this->_options['pluginname'];
                }
                repository::static_function($this->_typename, 'create', $this->_typename, 0, context_system::instance(), $instanceoptions);
            }
            //run plugin_init function
            if (!repository::static_function($this->_typename, 'plugin_init')) {
                $this->update_visibility(false);
                if (!$silent) {
                    throw new repository_exception('cannotinitplugin', 'repository');
                }
            }

            cache::make('core', 'repositories')->purge();
            if(!empty($plugin_id)) {
                // return plugin_id if create successfully
                return $plugin_id;
            } else {
                return false;
            }

        } else {
            if (!$silent) {
                throw new repository_exception('existingrepository', 'repository');
            }
            // If plugin existed, return false, tell caller no new plugins were created.
            return false;
        }
    }


    /**
     * Update plugin options into the config_plugin table
     *
     * @param array $options
     * @return bool
     */
    public function update_options($options = null) {
        global $DB;
        $classname = 'repository_' . $this->_typename;
        $instanceoptions = repository::static_function($this->_typename, 'get_instance_option_names');
        if (empty($instanceoptions)) {
            // update repository instance name if this plugin type doesn't have muliti instances
            $params = array();
            $params['type'] = $this->_typename;
            $instances = repository::get_instances($params);
            $instance = array_pop($instances);
            if ($instance) {
                $DB->set_field('repository_instances', 'name', $options['pluginname'], array('id'=>$instance->id));
            }
            unset($options['pluginname']);
        }

        if (!empty($options)) {
            $this->_options = $options;
        }

        foreach ($this->_options as $name => $value) {
            set_config($name, $value, $this->_typename);
        }

        cache::make('core', 'repositories')->purge();
        return true;
    }

    /**
     * Update visible database field with the value given as parameter
     * or with the visible value of this object
     * This function is private.
     * For public access, have a look to switch_and_update_visibility()
     *
     * @param bool $visible
     * @return bool
     */
    private function update_visible($visible = null) {
        global $DB;

        if (!empty($visible)) {
            $this->_visible = $visible;
        }
        else if (!isset($this->_visible)) {
            throw new repository_exception('updateemptyvisible', 'repository');
        }

        cache::make('core', 'repositories')->purge();
        return $DB->set_field('repository', 'visible', $this->_visible, array('type'=>$this->_typename));
    }

    /**
     * Update database sortorder field with the value given as parameter
     * or with the sortorder value of this object
     * This function is private.
     * For public access, have a look to move_order()
     *
     * @param int $sortorder
     * @return bool
     */
    private function update_sortorder($sortorder = null) {
        global $DB;

        if (!empty($sortorder) && $sortorder!=0) {
            $this->_sortorder = $sortorder;
        }
        //if sortorder is not set, we set it as the ;ast position in the list
        else if (!isset($this->_sortorder) || $this->_sortorder == 0 ) {
            $sql = "SELECT MAX(sortorder) FROM {repository}";
            $this->_sortorder = 1 + $DB->get_field_sql($sql);
        }

        cache::make('core', 'repositories')->purge();
        return $DB->set_field('repository', 'sortorder', $this->_sortorder, array('type'=>$this->_typename));
    }

    /**
     * Change order of the type with its adjacent upper or downer type
     * (database fields are updated)
     * Algorithm details:
     * 1. retrieve all types in an array. This array is sorted by sortorder,
     * and the array keys start from 0 to X (incremented by 1)
     * 2. switch sortorder values of this type and its adjacent type
     *
     * @param string $move "up" or "down"
     */
    public function move_order($move) {
        global $DB;

        $types = repository::get_types();    // retrieve all types

        // retrieve this type into the returned array
        $i = 0;
        while (!isset($indice) && $i<count($types)) {
            if ($types[$i]->get_typename() == $this->_typename) {
                $indice = $i;
            }
            $i++;
        }

        // retrieve adjacent indice
        switch ($move) {
            case "up":
                $adjacentindice = $indice - 1;
            break;
            case "down":
                $adjacentindice = $indice + 1;
            break;
            default:
            throw new repository_exception('movenotdefined', 'repository');
        }

        //switch sortorder of this type and the adjacent type
        //TODO: we could reset sortorder for all types. This is not as good in performance term, but
        //that prevent from wrong behaviour on a screwed database. As performance are not important in this particular case
        //it worth to change the algo.
        if ($adjacentindice>=0 && !empty($types[$adjacentindice])) {
            $DB->set_field('repository', 'sortorder', $this->_sortorder, array('type'=>$types[$adjacentindice]->get_typename()));
            $this->update_sortorder($types[$adjacentindice]->get_sortorder());
        }
    }

    /**
     * 1. Change visibility to the value chosen
     * 2. Update the type
     *
     * @param bool $visible
     * @return bool
     */
    public function update_visibility($visible = null) {
        if (is_bool($visible)) {
            $this->_visible = $visible;
        } else {
            $this->_visible = !$this->_visible;
        }
        return $this->update_visible();
    }


    /**
     * Delete a repository_type (general options are removed from config_plugin
     * table, and all instances are deleted)
     *
     * @param bool $downloadcontents download external contents if exist
     * @return bool
     */
    public function delete($downloadcontents = false) {
        global $DB;

        //delete all instances of this type
        $params = array();
        $params['context'] = array();
        $params['onlyvisible'] = false;
        $params['type'] = $this->_typename;
        $instances = repository::get_instances($params);
        foreach ($instances as $instance) {
            $instance->delete($downloadcontents);
        }

        //delete all general options
        foreach ($this->_options as $name => $value) {
            set_config($name, null, $this->_typename);
        }

        cache::make('core', 'repositories')->purge();
        try {
            $DB->delete_records('repository', array('type' => $this->_typename));
        } catch (dml_exception $ex) {
            return false;
        }
        return true;
    }

    /**
     * Prepares the repository type to be cached. Implements method from cacheable_object interface.
     *
     * @return array
     */
    public function prepare_to_cache() {
        return array(
            'typename' => $this->_typename,
            'typeoptions' => $this->_options,
            'visible' => $this->_visible,
            'sortorder' => $this->_sortorder
        );
    }

    /**
     * Restores repository type from cache. Implements method from cacheable_object interface.
     *
     * @return array
     */
    public static function wake_from_cache($data) {
        return new repository_type($data['typename'], $data['typeoptions'], $data['visible'], $data['sortorder']);
    }
}

/**
 * This is the base class of the repository class.
 *
 * To create repository plugin, see: {@link http://docs.moodle.org/dev/Repository_plugins}
 * See an example: {@link repository_boxnet}
 *
 * @package   core_repository
 * @copyright 2009 Dongsheng Cai {@link http://dongsheng.org}
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
abstract class repository implements cacheable_object {
    /** Timeout in seconds for downloading the external file into moodle */
    const GETFILE_TIMEOUT = 30;
    /** Timeout in seconds for syncronising the external file size */
    const SYNCFILE_TIMEOUT = 1;
    /** Timeout in seconds for downloading an image file from external repository during syncronisation */
    const SYNCIMAGE_TIMEOUT = 3;

    // $disabled can be set to true to disable a plugin by force
    // example: self::$disabled = true
    /** @var bool force disable repository instance */
    public $disabled = false;
    /** @var int repository instance id */
    public $id;
    /** @var stdClass current context */
    public $context;
    /** @var array repository options */
    public $options;
    /** @var bool Whether or not the repository instance is editable */
    public $readonly;
    /** @var int return types */
    public $returntypes;
    /** @var stdClass repository instance database record */
    public $instance;
    /** @var string Type of repository (webdav, google_docs, dropbox, ...). Read from $this->get_typename(). */
    protected $typename;

    /**
     * Constructor
     *
     * @param int $repositoryid repository instance id
     * @param int|stdClass $context a context id or context object
     * @param array $options repository options
     * @param int $readonly indicate this repo is readonly or not
     */
    public function __construct($repositoryid, $context = SYSCONTEXTID, $options = array(), $readonly = 0) {
        global $DB;
        $this->id = $repositoryid;
        if (is_object($context)) {
            $this->context = $context;
        } else {
            $this->context = context::instance_by_id($context);
        }
        $cache = cache::make('core', 'repositories');
        if (($this->instance = $cache->get('i:'. $this->id)) === false) {
            $this->instance = $DB->get_record_sql("SELECT i.*, r.type AS repositorytype, r.sortorder, r.visible
                      FROM {repository} r, {repository_instances} i
                     WHERE i.typeid = r.id and i.id = ?", array('id' => $this->id));
            $cache->set('i:'. $this->id, $this->instance);
        }
        $this->readonly = $readonly;
        $this->options = array();

        if (is_array($options)) {
            // The get_option() method will get stored options in database.
            $options = array_merge($this->get_option(), $options);
        } else {
            $options = $this->get_option();
        }
        foreach ($options as $n => $v) {
            $this->options[$n] = $v;
        }
        $this->name = $this->get_name();
        $this->returntypes = $this->supported_returntypes();
        $this->super_called = true;
    }

    /**
     * Magic method for non-existing (usually deprecated) class methods.
     *
     * @param string $name
     * @param array $arguments
     * @return mixed
     * @throws coding_exception
     */
    public function __call($name, $arguments) {
        if ($name === 'sync_individual_file') {
            // Method repository::sync_individual_file() was deprecated in Moodle 2.6.
            // See repository::sync_reference().
            debugging('Function repository::sync_individual_file() is deprecated.', DEBUG_DEVELOPER);
            return true;
        } else if ($name === 'get_file_by_reference') {
            // Method repository::get_file_by_reference() was deprecated in Moodle 2.6.
            // See repository::sync_reference().
            debugging('Function repository::get_file_by_reference() is deprecated.', DEBUG_DEVELOPER);
            return null;
        } else if ($name === 'get_reference_file_lifetime') {
            // Method repository::get_file_by_reference() was deprecated in Moodle 2.6.
            // See repository::sync_reference().
            debugging('Function repository::get_reference_file_lifetime() is deprecated.', DEBUG_DEVELOPER);
            return 24 * 60 * 60;
        } else {
            throw new coding_exception('Tried to call unknown method '.get_class($this).'::'.$name);
        }
    }

    /**
     * Get repository instance using repository id
     *
     * Note that this function does not check permission to access repository contents
     *
     * @throws repository_exception
     *
     * @param int $repositoryid repository instance ID
     * @param context|int $context context instance or context ID where this repository will be used
     * @param array $options additional repository options
     * @return repository
     */
    public static function get_repository_by_id($repositoryid, $context, $options = array()) {
        global $CFG, $DB;
        $cache = cache::make('core', 'repositories');
        if (!is_object($context)) {
            $context = context::instance_by_id($context);
        }
        $cachekey = 'rep:'. $repositoryid. ':'. $context->id. ':'. serialize($options);
        if ($repository = $cache->get($cachekey)) {
            return $repository;
        }

        if (!$record = $cache->get('i:'. $repositoryid)) {
            $sql = "SELECT i.*, r.type AS repositorytype, r.visible, r.sortorder
                      FROM {repository_instances} i
                      JOIN {repository} r ON r.id = i.typeid
                     WHERE i.id = ?";
            if (!$record = $DB->get_record_sql($sql, array($repositoryid))) {
                throw new repository_exception('invalidrepositoryid', 'repository');
            }
            $cache->set('i:'. $record->id, $record);
        }

        $type = $record->repositorytype;
        if (file_exists($CFG->dirroot . "/repository/$type/lib.php")) {
            require_once($CFG->dirroot . "/repository/$type/lib.php");
            $classname = 'repository_' . $type;
            $options['type'] = $type;
            $options['typeid'] = $record->typeid;
            $options['visible'] = $record->visible;
            if (empty($options['name'])) {
                $options['name'] = $record->name;
            }
            $repository = new $classname($repositoryid, $context, $options, $record->readonly);
            if (empty($repository->super_called)) {
                // to make sure the super construct is called
                debugging('parent::__construct must be called by '.$type.' plugin.');
            }
            $cache->set($cachekey, $repository);
            return $repository;
        } else {
            throw new repository_exception('invalidplugin', 'repository');
        }
    }

    /**
     * Returns the type name of the repository.
     *
     * @return string type name of the repository.
     * @since  2.5
     */
    public function get_typename() {
        if (empty($this->typename)) {
            $matches = array();
            if (!preg_match("/^repository_(.*)$/", get_class($this), $matches)) {
                throw new coding_exception('The class name of a repository should be repository_<typeofrepository>, '.
                        'e.g. repository_dropbox');
            }
            $this->typename = $matches[1];
        }
        return $this->typename;
    }

    /**
     * Get a repository type object by a given type name.
     *
     * @static
     * @param string $typename the repository type name
     * @return repository_type|bool
     */
    public static function get_type_by_typename($typename) {
        global $DB;
        $cache = cache::make('core', 'repositories');
        if (($repositorytype = $cache->get('typename:'. $typename)) === false) {
            $repositorytype = null;
            if ($record = $DB->get_record('repository', array('type' => $typename))) {
                $repositorytype = new repository_type($record->type, (array)get_config($record->type), $record->visible, $record->sortorder);
                $cache->set('typeid:'. $record->id, $repositorytype);
            }
            $cache->set('typename:'. $typename, $repositorytype);
        }
        return $repositorytype;
    }

    /**
     * Get the repository type by a given repository type id.
     *
     * @static
     * @param int $id the type id
     * @return object
     */
    public static function get_type_by_id($id) {
        global $DB;
        $cache = cache::make('core', 'repositories');
        if (($repositorytype = $cache->get('typeid:'. $id)) === false) {
            $repositorytype = null;
            if ($record = $DB->get_record('repository', array('id' => $id))) {
                $repositorytype = new repository_type($record->type, (array)get_config($record->type), $record->visible, $record->sortorder);
                $cache->set('typename:'. $record->type, $repositorytype);
            }
            $cache->set('typeid:'. $id, $repositorytype);
        }
        return $repositorytype;
    }

    /**
     * Return all repository types ordered by sortorder field
     * first repository type in returnedarray[0], second repository type in returnedarray[1], ...
     *
     * @static
     * @param bool $visible can return types by visiblity, return all types if null
     * @return array Repository types
     */
    public static function get_types($visible=null) {
        global $DB, $CFG;
        $cache = cache::make('core', 'repositories');
        if (!$visible) {
            $typesnames = $cache->get('types');
        } else {
            $typesnames = $cache->get('typesvis');
        }
        $types = array();
        if ($typesnames === false) {
            $typesnames = array();
            $vistypesnames = array();
            if ($records = $DB->get_records('repository', null ,'sortorder')) {
                foreach($records as $type) {
                    if (($repositorytype = $cache->get('typename:'. $type->type)) === false) {
                        // Create new instance of repository_type.
                        if (file_exists($CFG->dirroot . '/repository/'. $type->type .'/lib.php')) {
                            $repositorytype = new repository_type($type->type, (array)get_config($type->type), $type->visible, $type->sortorder);
                            $cache->set('typeid:'. $type->id, $repositorytype);
                            $cache->set('typename:'. $type->type, $repositorytype);
                        }
                    }
                    if ($repositorytype) {
                        if (empty($visible) || $repositorytype->get_visible()) {
                            $types[] = $repositorytype;
                            $vistypesnames[] = $repositorytype->get_typename();
                        }
                        $typesnames[] = $repositorytype->get_typename();
                    }
                }
            }
            $cache->set('types', $typesnames);
            $cache->set('typesvis', $vistypesnames);
        } else {
            foreach ($typesnames as $typename) {
                $types[] = self::get_type_by_typename($typename);
            }
        }
        return $types;
    }

    /**
     * Checks if user has a capability to view the current repository.
     *
     * @return bool true when the user can, otherwise throws an exception.
     * @throws repository_exception when the user does not meet the requirements.
     */
    public final function check_capability() {
        global $USER;

        // The context we are on.
        $currentcontext = $this->context;

        // Ensure that the user can view the repository in the current context.
        $can = has_capability('repository/'.$this->get_typename().':view', $currentcontext);

        // Context in which the repository has been created.
        $repocontext = context::instance_by_id($this->instance->contextid);

        // Prevent access to private repositories when logged in as.
        if ($can && \core\session\manager::is_loggedinas()) {
            if ($this->contains_private_data() || $repocontext->contextlevel == CONTEXT_USER) {
                $can = false;
            }
        }

        // We are going to ensure that the current context was legit, and reliable to check
        // the capability against. (No need to do that if we already cannot).
        if ($can) {
            if ($repocontext->contextlevel == CONTEXT_USER) {
                // The repository is a user instance, ensure we're the right user to access it!
                if ($repocontext->instanceid != $USER->id) {
                    $can = false;
                }
            } else if ($repocontext->contextlevel == CONTEXT_COURSE) {
                // The repository is a course one. Let's check that we are on the right course.
                if (in_array($currentcontext->contextlevel, array(CONTEXT_COURSE, CONTEXT_MODULE, CONTEXT_BLOCK))) {
                    $coursecontext = $currentcontext->get_course_context();
                    if ($coursecontext->instanceid != $repocontext->instanceid) {
                        $can = false;
                    }
                } else {
                    // We are on a parent context, therefore it's legit to check the permissions
                    // in the current context.
                }
            } else {
                // Nothing to check here, system instances can have different permissions on different
                // levels. We do not want to prevent URL hack here, because it does not make sense to
                // prevent a user to access a repository in a context if it's accessible in another one.
            }
        }

        if ($can) {
            return true;
        }

        throw new repository_exception('nopermissiontoaccess', 'repository');
    }

    /**
     * Check if file already exists in draft area.
     *
     * @static
     * @param int $itemid of the draft area.
     * @param string $filepath path to the file.
     * @param string $filename file name.
     * @return bool
     */
    public static function draftfile_exists($itemid, $filepath, $filename) {
        global $USER;
        $fs = get_file_storage();
        $usercontext = context_user::instance($USER->id);
        return $fs->file_exists($usercontext->id, 'user', 'draft', $itemid, $filepath, $filename);
    }

    /**
     * Parses the moodle file reference and returns an instance of stored_file
     *
     * @param string $reference reference to the moodle internal file as retruned by
     *        {@link repository::get_file_reference()} or {@link file_storage::pack_reference()}
     * @return stored_file|null
     */
    public static function get_moodle_file($reference) {
        $params = file_storage::unpack_reference($reference, true);
        $fs = get_file_storage();
        return $fs->get_file($params['contextid'], $params['component'], $params['filearea'],
                    $params['itemid'], $params['filepath'], $params['filename']);
    }

    /**
     * Repository method to make sure that user can access particular file.
     *
     * This is checked when user tries to pick the file from repository to deal with
     * potential parameter substitutions is request
     *
     * @param string $source source of the file, returned by repository as 'source' and received back from user (not cleaned)
     * @return bool whether the file is accessible by current user
     */
    public function file_is_accessible($source) {
        if ($this->has_moodle_files()) {
            $reference = $this->get_file_reference($source);
            try {
                $params = file_storage::unpack_reference($reference, true);
            } catch (file_reference_exception $e) {
                return false;
            }
            $browser = get_file_browser();
            $context = context::instance_by_id($params['contextid']);
            $file_info = $browser->get_file_info($context, $params['component'], $params['filearea'],
                    $params['itemid'], $params['filepath'], $params['filename']);
            return !empty($file_info);
        }
        return true;
    }

    /**
     * This function is used to copy a moodle file to draft area.
     *
     * It DOES NOT check if the user is allowed to access this file because the actual file
     * can be located in the area where user does not have access to but there is an alias
     * to this file in the area where user CAN access it.
     * {@link file_is_accessible} should be called for alias location before calling this function.
     *
     * @param string $source The metainfo of file, it is base64 encoded php serialized data
     * @param stdClass|array $filerecord contains itemid, filepath, filename and optionally other
     *      attributes of the new file
     * @param int $maxbytes maximum allowed size of file, -1 if unlimited. If size of file exceeds
     *      the limit, the file_exception is thrown.
     * @param int $areamaxbytes the maximum size of the area. A file_exception is thrown if the
     *      new file will reach the limit.
     * @return array The information about the created file
     */
    public function copy_to_area($source, $filerecord, $maxbytes = -1, $areamaxbytes = FILE_AREA_MAX_BYTES_UNLIMITED) {
        global $USER;
        $fs = get_file_storage();

        if ($this->has_moodle_files() == false) {
            throw new coding_exception('Only repository used to browse moodle files can use repository::copy_to_area()');
        }

        $user_context = context_user::instance($USER->id);

        $filerecord = (array)$filerecord;
        // make sure the new file will be created in user draft area
        $filerecord['component'] = 'user';
        $filerecord['filearea'] = 'draft';
        $filerecord['contextid'] = $user_context->id;
        $draftitemid = $filerecord['itemid'];
        $new_filepath = $filerecord['filepath'];
        $new_filename = $filerecord['filename'];

        // the file needs to copied to draft area
        $stored_file = self::get_moodle_file($source);
        if ($maxbytes != -1 && $stored_file->get_filesize() > $maxbytes) {
            throw new file_exception('maxbytes');
        }
        // Validate the size of the draft area.
        if (file_is_draft_area_limit_reached($draftitemid, $areamaxbytes, $stored_file->get_filesize())) {
            throw new file_exception('maxareabytes');
        }

        if (repository::draftfile_exists($draftitemid, $new_filepath, $new_filename)) {
            // create new file
            $unused_filename = repository::get_unused_filename($draftitemid, $new_filepath, $new_filename);
            $filerecord['filename'] = $unused_filename;
            $fs->create_file_from_storedfile($filerecord, $stored_file);
            $event = array();
            $event['event'] = 'fileexists';
            $event['newfile'] = new stdClass;
            $event['newfile']->filepath = $new_filepath;
            $event['newfile']->filename = $unused_filename;
            $event['newfile']->url = moodle_url::make_draftfile_url($draftitemid, $new_filepath, $unused_filename)->out();
            $event['existingfile'] = new stdClass;
            $event['existingfile']->filepath = $new_filepath;
            $event['existingfile']->filename = $new_filename;
            $event['existingfile']->url = moodle_url::make_draftfile_url($draftitemid, $new_filepath, $new_filename)->out();
            return $event;
        } else {
            $fs->create_file_from_storedfile($filerecord, $stored_file);
            $info = array();
            $info['itemid'] = $draftitemid;
            $info['file'] = $new_filename;
            $info['title'] = $new_filename;
            $info['contextid'] = $user_context->id;
            $info['url'] = moodle_url::make_draftfile_url($draftitemid, $new_filepath, $new_filename)->out();
            $info['filesize'] = $stored_file->get_filesize();
            return $info;
        }
    }

    /**
     * Get an unused filename from the current draft area.
     *
     * Will check if the file ends with ([0-9]) and increase the number.
     *
     * @static
     * @param int $itemid draft item ID.
     * @param string $filepath path to the file.
     * @param string $filename name of the file.
     * @return string an unused file name.
     */
    public static function get_unused_filename($itemid, $filepath, $filename) {
        global $USER;
        $contextid = context_user::instance($USER->id)->id;
        $fs = get_file_storage();
        return $fs->get_unused_filename($contextid, 'user', 'draft', $itemid, $filepath, $filename);
    }

    /**
     * Append a suffix to filename.
     *
     * @static
     * @param string $filename
     * @return string
     * @deprecated since 2.5
     */
    public static function append_suffix($filename) {
        debugging('The function repository::append_suffix() has been deprecated. Use repository::get_unused_filename() instead.',
            DEBUG_DEVELOPER);
        $pathinfo = pathinfo($filename);
        if (empty($pathinfo['extension'])) {
            return $filename . RENAME_SUFFIX;
        } else {
            return $pathinfo['filename'] . RENAME_SUFFIX . '.' . $pathinfo['extension'];
        }
    }

    /**
     * Return all types that you a user can create/edit and which are also visible
     * Note: Mostly used in order to know if at least one editable type can be set
     *
     * @static
     * @param stdClass $context the context for which we want the editable types
     * @return array types
     */
    public static function get_editable_types($context = null) {

        if (empty($context)) {
            $context = context_system::instance();
        }

        $types= repository::get_types(true);
        $editabletypes = array();
        foreach ($types as $type) {
            $instanceoptionnames = repository::static_function($type->get_typename(), 'get_instance_option_names');
            if (!empty($instanceoptionnames)) {
                if ($type->get_contextvisibility($context)) {
                    $editabletypes[]=$type;
                }
             }
        }
        return $editabletypes;
    }

    /**
     * Return repository instances
     *
     * @static
     * @param array $args Array containing the following keys:
     *           currentcontext : instance of context (default system context)
     *           context : array of instances of context (default empty array)
     *           onlyvisible : bool (default true)
     *           type : string return instances of this type only
     *           accepted_types : string|array return instances that contain files of those types (*, web_image, .pdf, ...)
     *           return_types : int combination of FILE_INTERNAL & FILE_EXTERNAL & FILE_REFERENCE.
     *                          0 means every type. The default is FILE_INTERNAL | FILE_EXTERNAL.
     *           userid : int if specified, instances belonging to other users will not be returned
     *
     * @return array repository instances
     */
    public static function get_instances($args = array()) {
        global $DB, $CFG, $USER;

        // Fill $args attributes with default values unless specified
        if (!isset($args['currentcontext']) || !($args['currentcontext'] instanceof context)) {
            $current_context = context_system::instance();
        } else {
            $current_context = $args['currentcontext'];
        }
        $args['currentcontext'] = $current_context->id;
        $contextids = array();
        if (!empty($args['context'])) {
            foreach ($args['context'] as $context) {
                $contextids[] = $context->id;
            }
        }
        $args['context'] = $contextids;
        if (!isset($args['onlyvisible'])) {
            $args['onlyvisible'] = true;
        }
        if (!isset($args['return_types'])) {
            $args['return_types'] = FILE_INTERNAL | FILE_EXTERNAL;
        }
        if (!isset($args['type'])) {
            $args['type'] = null;
        }
        if (empty($args['disable_types']) || !is_array($args['disable_types'])) {
            $args['disable_types'] = null;
        }
        if (empty($args['userid']) || !is_numeric($args['userid'])) {
            $args['userid'] = null;
        }
        if (!isset($args['accepted_types']) || (is_array($args['accepted_types']) && in_array('*', $args['accepted_types']))) {
            $args['accepted_types'] = '*';
        }
        ksort($args);
        $cachekey = 'all:'. serialize($args);

        // Check if we have cached list of repositories with the same query
        $cache = cache::make('core', 'repositories');
        if (($cachedrepositories = $cache->get($cachekey)) !== false) {
            // convert from cacheable_object_array to array
            $repositories = array();
            foreach ($cachedrepositories as $repository) {
                $repositories[$repository->id] = $repository;
            }
            return $repositories;
        }

        // Prepare DB SQL query to retrieve repositories
        $params = array();
        $sql = "SELECT i.*, r.type AS repositorytype, r.sortorder, r.visible
                  FROM {repository} r, {repository_instances} i
                 WHERE i.typeid = r.id ";

        if ($args['disable_types']) {
            list($types, $p) = $DB->get_in_or_equal($args['disable_types'], SQL_PARAMS_NAMED, 'distype', false);
            $sql .= " AND r.type $types";
            $params = array_merge($params, $p);
        }

        if ($args['userid']) {
            $sql .= " AND (i.userid = 0 or i.userid = :userid)";
            $params['userid'] = $args['userid'];
        }

        if ($args['context']) {
            list($ctxsql, $p2) = $DB->get_in_or_equal($args['context'], SQL_PARAMS_NAMED, 'ctx');
            $sql .= " AND i.contextid $ctxsql";
            $params = array_merge($params, $p2);
        }

        if ($args['onlyvisible'] == true) {
            $sql .= " AND r.visible = 1";
        }

        if ($args['type'] !== null) {
            $sql .= " AND r.type = :type";
            $params['type'] = $args['type'];
        }
        $sql .= " ORDER BY r.sortorder, i.name";

        if (!$records = $DB->get_records_sql($sql, $params)) {
            $records = array();
        }

        $repositories = array();
        // Sortorder should be unique, which is not true if we use $record->sortorder
        // and there are multiple instances of any repository type
        $sortorder = 1;
        foreach ($records as $record) {
            $cache->set('i:'. $record->id, $record);
            if (!file_exists($CFG->dirroot . '/repository/'. $record->repositorytype.'/lib.php')) {
                continue;
            }
            $repository = self::get_repository_by_id($record->id, $current_context);
            $repository->options['sortorder'] = $sortorder++;

            $is_supported = true;

            // check mimetypes
            if ($args['accepted_types'] !== '*' and $repository->supported_filetypes() !== '*') {
                $accepted_ext = file_get_typegroup('extension', $args['accepted_types']);
                $supported_ext = file_get_typegroup('extension', $repository->supported_filetypes());
                $valid_ext = array_intersect($accepted_ext, $supported_ext);
                $is_supported = !empty($valid_ext);
            }
            // Check return values.
            if (!empty($args['return_types']) && !($repository->supported_returntypes() & $args['return_types'])) {
                $is_supported = false;
            }

            if (!$args['onlyvisible'] || ($repository->is_visible() && !$repository->disabled)) {
                // check capability in current context
                $capability = has_capability('repository/'.$record->repositorytype.':view', $current_context);
                if ($record->repositorytype == 'coursefiles') {
                    // coursefiles plugin needs managefiles permission
                    $capability = $capability && has_capability('moodle/course:managefiles', $current_context);
                }
                if ($is_supported && $capability) {
                    $repositories[$repository->id] = $repository;
                }
            }
        }
        $cache->set($cachekey, new cacheable_object_array($repositories));
        return $repositories;
    }

    /**
     * Get single repository instance for administrative actions
     *
     * Do not use this function to access repository contents, because it
     * does not set the current context
     *
     * @see repository::get_repository_by_id()
     *
     * @static
     * @param integer $id repository instance id
     * @return repository
     */
    public static function get_instance($id) {
        return self::get_repository_by_id($id, context_system::instance());
    }

    /**
     * Call a static function. Any additional arguments than plugin and function will be passed through.
     *
     * @static
     * @param string $plugin repository plugin name
     * @param string $function function name
     * @return mixed
     */
    public static function static_function($plugin, $function) {
        global $CFG;

        //check that the plugin exists
        $typedirectory = $CFG->dirroot . '/repository/'. $plugin . '/lib.php';
        if (!file_exists($typedirectory)) {
            //throw new repository_exception('invalidplugin', 'repository');
            return false;
        }

        $args = func_get_args();
        if (count($args) <= 2) {
            $args = array();
        } else {
            array_shift($args);
            array_shift($args);
        }

        require_once($typedirectory);
        return call_user_func_array(array('repository_' . $plugin, $function), $args);
    }

    /**
     * Scan file, throws exception in case of infected file.
     *
     * Please note that the scanning engine must be able to access the file,
     * permissions of the file are not modified here!
     *
     * @static
     * @param string $thefile
     * @param string $filename name of the file
     * @param bool $deleteinfected
     */
    public static function antivir_scan_file($thefile, $filename, $deleteinfected) {
        global $CFG;

        if (!is_readable($thefile)) {
            // this should not happen
            return;
        }

        if (empty($CFG->runclamonupload) or empty($CFG->pathtoclam)) {
            // clam not enabled
            return;
        }

        $CFG->pathtoclam = trim($CFG->pathtoclam);

        if (!file_exists($CFG->pathtoclam) or !is_executable($CFG->pathtoclam)) {
            // misconfigured clam - use the old notification for now
            require("$CFG->libdir/uploadlib.php");
            $notice = get_string('clamlost', 'moodle', $CFG->pathtoclam);
            clam_message_admins($notice);
            return;
        }

        $clamparam = ' --stdout ';
        // If we are dealing with clamdscan, clamd is likely run as a different user
        // that might not have permissions to access your file.
        // To make clamdscan work, we use --fdpass parameter that passes the file
        // descriptor permissions to clamd, which allows it to scan given file
        // irrespective of directory and file permissions.
        if (basename($CFG->pathtoclam) == 'clamdscan') {
            $clamparam .= '--fdpass ';
        }
        // execute test
        $cmd = escapeshellcmd($CFG->pathtoclam).$clamparam.escapeshellarg($thefile);
        exec($cmd, $output, $return);

        if ($return == 0) {
            // perfect, no problem found
            return;

        } else if ($return == 1) {
            // infection found
            if ($deleteinfected) {
                unlink($thefile);
            }
            throw new moodle_exception('virusfounduser', 'moodle', '', array('filename'=>$filename));

        } else {
            //unknown problem
            require("$CFG->libdir/uploadlib.php");
            $notice = get_string('clamfailed', 'moodle', get_clam_error_code($return));
            $notice .= "\n\n". implode("\n", $output);
            clam_message_admins($notice);
            if ($CFG->clamfailureonupload === 'actlikevirus') {
                if ($deleteinfected) {
                    unlink($thefile);
                }
                throw new moodle_exception('virusfounduser', 'moodle', '', array('filename'=>$filename));
            } else {
                return;
            }
        }
    }

    /**
     * Repository method to serve the referenced file
     *
     * @see send_stored_file
     *
     * @param stored_file $storedfile the file that contains the reference
     * @param int $lifetime Number of seconds before the file should expire from caches (null means $CFG->filelifetime)
     * @param int $filter 0 (default)=no filtering, 1=all files, 2=html files only
     * @param bool $forcedownload If true (default false), forces download of file rather than view in browser/plugin
     * @param array $options additional options affecting the file serving
     */
    public function send_file($storedfile, $lifetime=null , $filter=0, $forcedownload=false, array $options = null) {
        if ($this->has_moodle_files()) {
            $fs = get_file_storage();
            $params = file_storage::unpack_referenc…

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