/mod/assign/locallib.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 the definition for the class assignment
 *
 * This class provides all the functionality for the new assign module.
 *
 * @package   mod_assign
 * @copyright 2012 NetSpot {@link http://www.netspot.com.au}
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

/**
 * Assignment submission statuses
 */
define('ASSIGN_SUBMISSION_STATUS_DRAFT', 'draft'); // student thinks it is a draft
define('ASSIGN_SUBMISSION_STATUS_SUBMITTED', 'submitted'); // student thinks it is finished

/**
 * Search filters for grading page
 */
define('ASSIGN_FILTER_SUBMITTED', 'submitted');
define('ASSIGN_FILTER_SINGLE_USER', 'singleuser');
define('ASSIGN_FILTER_REQUIRE_GRADING', 'require_grading');

/** Include accesslib.php */
require_once($CFG->libdir.'/accesslib.php');
/** Include formslib.php */
require_once($CFG->libdir.'/formslib.php');
/** Include repository/lib.php */
require_once($CFG->dirroot . '/repository/lib.php');
/** Include local mod_form.php */
require_once($CFG->dirroot.'/mod/assign/mod_form.php');
/** gradelib.php */
require_once($CFG->libdir.'/gradelib.php');
/** grading lib.php */
require_once($CFG->dirroot.'/grade/grading/lib.php');
/** Include feedbackplugin.php */
require_once($CFG->dirroot.'/mod/assign/feedbackplugin.php');
/** Include submissionplugin.php */
require_once($CFG->dirroot.'/mod/assign/submissionplugin.php');
/** Include renderable.php */
require_once($CFG->dirroot.'/mod/assign/renderable.php');
/** Include gradingtable.php */
require_once($CFG->dirroot.'/mod/assign/gradingtable.php');
/** Include eventslib.php */
require_once($CFG->libdir.'/eventslib.php');


/**
 * Standard base class for mod_assign (assignment types).
 *
 * @package   mod_assign
 * @copyright 2012 NetSpot {@link http://www.netspot.com.au}
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class assign {


    /** @var stdClass the assignment record that contains the global settings for this assign instance */
    private $instance;

    /** @var context the context of the course module for this assign instance (or just the course if we are
        creating a new one) */
    private $context;

    /** @var stdClass the course this assign instance belongs to */
    private $course;

    /** @var stdClass the admin config for all assign instances  */
    private $adminconfig;


    /** @var assign_renderer the custom renderer for this module */
    private $output;

    /** @var stdClass the course module for this assign instance */
    private $coursemodule;

    /** @var array cache for things like the coursemodule name or the scale menu - only lives for a single
        request */
    private $cache;

    /** @var array list of the installed submission plugins */
    private $submissionplugins;

    /** @var array list of the installed feedback plugins */
    private $feedbackplugins;

    /** @var string action to be used to return to this page (without repeating any form submissions etc.) */
    private $returnaction = 'view';

    /** @var array params to be used to return to this page */
    private $returnparams = array();

    /** @var string modulename prevents excessive calls to get_string */
    private static $modulename = null;

    /** @var string modulenameplural prevents excessive calls to get_string */
    private static $modulenameplural = null;

    /**
     * Constructor for the base assign class
     *
     * @param mixed $coursemodulecontext context|null the course module context (or the course context if the coursemodule has not been created yet)
     * @param mixed $coursemodule the current course module if it was already loaded - otherwise this class will load one from the context as required
     * @param mixed $course the current course  if it was already loaded - otherwise this class will load one from the context as required
     */
    public function __construct($coursemodulecontext, $coursemodule, $course) {
        global $PAGE;

        $this->context = $coursemodulecontext;
        $this->coursemodule = $coursemodule;
        $this->course = $course;
        $this->cache = array(); // temporary cache only lives for a single request - used to reduce db lookups

        $this->submissionplugins = $this->load_plugins('assignsubmission');
        $this->feedbackplugins = $this->load_plugins('assignfeedback');
        $this->output = $PAGE->get_renderer('mod_assign');
    }

    /**
     * Set the action and parameters that can be used to return to the current page
     *
     * @param string $action The action for the current page
     * @param array $params An array of name value pairs which form the parameters to return to the current page
     * @return void
     */
    public function register_return_link($action, $params) {
        $this->returnaction = $action;
        $this->returnparams = $params;
    }

    /**
     * Return an action that can be used to get back to the current page
     * @return string action
     */
    public function get_return_action() {
        return $this->returnaction;
    }

    /**
     * Based on the current assignment settings should we display the intro
     * @return bool showintro
     */
    private function show_intro() {
        if ($this->get_instance()->alwaysshowdescription ||
                time() > $this->get_instance()->allowsubmissionsfromdate) {
            return true;
        }
        return false;
    }

    /**
     * Return a list of parameters that can be used to get back to the current page
     * @return array params
     */
    public function get_return_params() {
        return $this->returnparams;
    }

    /**
     * Set the submitted form data
     * @param stdClass $data The form data (instance)
     */
    public function set_instance(stdClass $data) {
        $this->instance = $data;
    }

    /**
     * Set the context
     * @param context $context The new context
     */
    public function set_context(context $context) {
        $this->context = $context;
    }

    /**
     * Set the course data
     * @param stdClass $course The course data
     */
    public function set_course(stdClass $course) {
        $this->course = $course;
    }

    /**
     * get list of feedback plugins installed
     * @return array
     */
    public function get_feedback_plugins() {
        return $this->feedbackplugins;
    }

    /**
     * get list of submission plugins installed
     * @return array
     */
    public function get_submission_plugins() {
        return $this->submissionplugins;
    }


    /**
     * get a specific submission plugin by its type
     * @param string $subtype assignsubmission | assignfeedback
     * @param string $type
     * @return mixed assign_plugin|null
     */
    private function get_plugin_by_type($subtype, $type) {
        $shortsubtype = substr($subtype, strlen('assign'));
        $name = $shortsubtype . 'plugins';
        $pluginlist = $this->$name;
        foreach ($pluginlist as $plugin) {
            if ($plugin->get_type() == $type) {
                return $plugin;
            }
        }
        return null;
    }

    /**
     * Get a feedback plugin by type
     * @param string $type - The type of plugin e.g comments
     * @return mixed assign_feedback_plugin|null
     */
    public function get_feedback_plugin_by_type($type) {
        return $this->get_plugin_by_type('assignfeedback', $type);
    }

    /**
     * Get a submission plugin by type
     * @param string $type - The type of plugin e.g comments
     * @return mixed assign_submission_plugin|null
     */
    public function get_submission_plugin_by_type($type) {
        return $this->get_plugin_by_type('assignsubmission', $type);
    }

    /**
     * Load the plugins from the sub folders under subtype
     * @param string $subtype - either submission or feedback
     * @return array - The sorted list of plugins
     */
    private function load_plugins($subtype) {
        global $CFG;
        $result = array();

        $names = get_plugin_list($subtype);

        foreach ($names as $name => $path) {
            if (file_exists($path . '/locallib.php')) {
                require_once($path . '/locallib.php');

                $shortsubtype = substr($subtype, strlen('assign'));
                $pluginclass = 'assign_' . $shortsubtype . '_' . $name;

                $plugin = new $pluginclass($this, $name);

                if ($plugin instanceof assign_plugin) {
                    $idx = $plugin->get_sort_order();
                    while (array_key_exists($idx, $result)) $idx +=1;
                    $result[$idx] = $plugin;
                }
            }
        }
        ksort($result);
        return $result;
    }


    /**
     * Display the assignment, used by view.php
     *
     * The assignment is displayed differently depending on your role,
     * the settings for the assignment and the status of the assignment.
     * @param string $action The current action if any.
     * @return void
     */
    public function view($action='') {

        $o = '';
        $mform = null;

        // handle form submissions first
        if ($action == 'savesubmission') {
            $action = 'editsubmission';
            if ($this->process_save_submission($mform)) {
                $action = 'view';
            }
         } else if ($action == 'lock') {
            $this->process_lock();
            $action = 'grading';
         } else if ($action == 'reverttodraft') {
            $this->process_revert_to_draft();
            $action = 'grading';
         } else if ($action == 'unlock') {
            $this->process_unlock();
            $action = 'grading';
         } else if ($action == 'confirmsubmit') {
            $this->process_submit_for_grading();
            // save and show next button
         } else if ($action == 'batchgradingoperation') {
            $this->process_batch_grading_operation();
            $action = 'grading';
         } else if ($action == 'submitgrade') {
            if (optional_param('saveandshownext', null, PARAM_ALPHA)) {
                //save and show next
                $action = 'grade';
                if ($this->process_save_grade($mform)) {
                    $action = 'nextgrade';
                }
            } else if (optional_param('nosaveandprevious', null, PARAM_ALPHA)) {
                $action = 'previousgrade';
            } else if (optional_param('nosaveandnext', null, PARAM_ALPHA)) {
                //show next button
                $action = 'nextgrade';
            } else if (optional_param('savegrade', null, PARAM_ALPHA)) {
                //save changes button
                $action = 'grade';
                if ($this->process_save_grade($mform)) {
                    $action = 'grading';
                }
            } else {
                //cancel button
                $action = 'grading';
            }
        }else if ($action == 'quickgrade') {
            $message = $this->process_save_quick_grades();
            $action = 'quickgradingresult';
        }else if ($action == 'saveoptions') {
            $this->process_save_grading_options();
            $action = 'grading';
        }

        $returnparams = array('rownum'=>optional_param('rownum', 0, PARAM_INT));
        $this->register_return_link($action, $returnparams);

        // now show the right view page
        if ($action == 'previousgrade') {
            $mform = null;
            $o .= $this->view_single_grade_page($mform, -1);
        } else if ($action == 'quickgradingresult') {
            $mform = null;
            $o .= $this->view_quickgrading_result($message);
        } else if ($action == 'nextgrade') {
            $mform = null;
            $o .= $this->view_single_grade_page($mform, 1);
        } else if ($action == 'grade') {
            $o .= $this->view_single_grade_page($mform);
        } else if ($action == 'viewpluginassignfeedback') {
            $o .= $this->view_plugin_content('assignfeedback');
        } else if ($action == 'viewpluginassignsubmission') {
            $o .= $this->view_plugin_content('assignsubmission');
        } else if ($action == 'editsubmission') {
            $o .= $this->view_edit_submission_page($mform);
        } else if ($action == 'grading') {
            $o .= $this->view_grading_page();
        } else if ($action == 'downloadall') {
            $o .= $this->download_submissions();
        } else if ($action == 'submit') {
            $o .= $this->check_submit_for_grading();
        } else {
            $o .= $this->view_submission_page();
        }

        return $o;
    }


    /**
     * Add this instance to the database
     *
     * @param stdClass $formdata The data submitted from the form
     * @param bool $callplugins This is used to skip the plugin code
     *             when upgrading an old assignment to a new one (the plugins get called manually)
     * @return mixed false if an error occurs or the int id of the new instance
     */
    public function add_instance(stdClass $formdata, $callplugins) {
        global $DB;

        $err = '';

        // add the database record
        $update = new stdClass();
        $update->name = $formdata->name;
        $update->timemodified = time();
        $update->timecreated = time();
        $update->course = $formdata->course;
        $update->courseid = $formdata->course;
        $update->intro = $formdata->intro;
        $update->introformat = $formdata->introformat;
        $update->alwaysshowdescription = $formdata->alwaysshowdescription;
        $update->preventlatesubmissions = $formdata->preventlatesubmissions;
        $update->submissiondrafts = $formdata->submissiondrafts;
        $update->sendnotifications = $formdata->sendnotifications;
        $update->sendlatenotifications = $formdata->sendlatenotifications;
        $update->duedate = $formdata->duedate;
        $update->allowsubmissionsfromdate = $formdata->allowsubmissionsfromdate;
        $update->grade = $formdata->grade;
        $returnid = $DB->insert_record('assign', $update);
        $this->instance = $DB->get_record('assign', array('id'=>$returnid), '*', MUST_EXIST);
        // cache the course record
        $this->course = $DB->get_record('course', array('id'=>$formdata->course), '*', MUST_EXIST);

        if ($callplugins) {
            // call save_settings hook for submission plugins
            foreach ($this->submissionplugins as $plugin) {
                if (!$this->update_plugin_instance($plugin, $formdata)) {
                    print_error($plugin->get_error());
                    return false;
                }
            }
            foreach ($this->feedbackplugins as $plugin) {
                if (!$this->update_plugin_instance($plugin, $formdata)) {
                    print_error($plugin->get_error());
                    return false;
                }
            }

            // in the case of upgrades the coursemodule has not been set so we need to wait before calling these two
            // TODO: add event to the calendar
            $this->update_calendar($formdata->coursemodule);
            // TODO: add the item in the gradebook
            $this->update_gradebook(false, $formdata->coursemodule);

        }

        $update = new stdClass();
        $update->id = $this->get_instance()->id;
        $update->nosubmissions = (!$this->is_any_submission_plugin_enabled()) ? 1: 0;
        $DB->update_record('assign', $update);

        return $returnid;
    }

    /**
     * Delete all grades from the gradebook for this assignment
     *
     * @return bool
     */
    private function delete_grades() {
        global $CFG;

        return grade_update('mod/assign', $this->get_course()->id, 'mod', 'assign', $this->get_instance()->id, 0, NULL, array('deleted'=>1)) == GRADE_UPDATE_OK;
    }

    /**
     * Delete this instance from the database
     *
     * @return bool false if an error occurs
     */
    public function delete_instance() {
        global $DB;
        $result = true;

        foreach ($this->submissionplugins as $plugin) {
            if (!$plugin->delete_instance()) {
                print_error($plugin->get_error());
                $result = false;
            }
        }
        foreach ($this->feedbackplugins as $plugin) {
            if (!$plugin->delete_instance()) {
                print_error($plugin->get_error());
                $result = false;
            }
        }

        // delete files associated with this assignment
        $fs = get_file_storage();
        if (! $fs->delete_area_files($this->context->id) ) {
            $result = false;
        }

        // delete_records will throw an exception if it fails - so no need for error checking here

        $DB->delete_records('assign_submission', array('assignment'=>$this->get_instance()->id));
        $DB->delete_records('assign_grades', array('assignment'=>$this->get_instance()->id));
        $DB->delete_records('assign_plugin_config', array('assignment'=>$this->get_instance()->id));

        // delete items from the gradebook
        if (! $this->delete_grades()) {
            $result = false;
        }

        // delete the instance
        $DB->delete_records('assign', array('id'=>$this->get_instance()->id));

        return $result;
    }

    /**
     * Update the settings for a single plugin
     *
     * @param assign_plugin $plugin The plugin to update
     * @param stdClass $formdata The form data
     * @return bool false if an error occurs
     */
    private function update_plugin_instance(assign_plugin $plugin, stdClass $formdata) {
        if ($plugin->is_visible()) {
            $enabledname = $plugin->get_subtype() . '_' . $plugin->get_type() . '_enabled';
            if ($formdata->$enabledname) {
                $plugin->enable();
                if (!$plugin->save_settings($formdata)) {
                    print_error($plugin->get_error());
                    return false;
                }
            } else {
                $plugin->disable();
            }
        }
        return true;
    }

    /**
     * Update the gradebook information for this assignment
     *
     * @param bool $reset If true, will reset all grades in the gradbook for this assignment
     * @param int $coursemoduleid This is required because it might not exist in the database yet
     * @return bool
     */
    public function update_gradebook($reset, $coursemoduleid) {
         global $CFG;
        /** Include lib.php */
        require_once($CFG->dirroot.'/mod/assign/lib.php');
        $assign = clone $this->get_instance();
        $assign->cmidnumber = $coursemoduleid;
        $param = null;
        if ($reset) {
            $param = 'reset';
        }

        return assign_grade_item_update($assign, $param);
    }

    /** Load and cache the admin config for this module
     *
     * @return stdClass the plugin config
     */
    public function get_admin_config() {
        if ($this->adminconfig) {
            return $this->adminconfig;
        }
        $this->adminconfig = get_config('assign');
        return $this->adminconfig;
    }


    /**
     * Update the calendar entries for this assignment
     *
     * @param int $coursemoduleid - Required to pass this in because it might not exist in the database yet
     * @return bool
     */
    public function update_calendar($coursemoduleid) {
        global $DB, $CFG;
        require_once($CFG->dirroot.'/calendar/lib.php');

        // special case for add_instance as the coursemodule has not been set yet.

        if ($this->get_instance()->duedate) {
            $event = new stdClass();

            if ($event->id = $DB->get_field('event', 'id', array('modulename'=>'assign', 'instance'=>$this->get_instance()->id))) {

                $event->name        = $this->get_instance()->name;

                $event->description = format_module_intro('assign', $this->get_instance(), $coursemoduleid);
                $event->timestart   = $this->get_instance()->duedate;

                $calendarevent = calendar_event::load($event->id);
                $calendarevent->update($event);
            } else {
                $event = new stdClass();
                $event->name        = $this->get_instance()->name;
                $event->description = format_module_intro('assign', $this->get_instance(), $coursemoduleid);
                $event->courseid    = $this->get_instance()->course;
                $event->groupid     = 0;
                $event->userid      = 0;
                $event->modulename  = 'assign';
                $event->instance    = $this->get_instance()->id;
                $event->eventtype   = 'due';
                $event->timestart   = $this->get_instance()->duedate;
                $event->timeduration = 0;

                calendar_event::create($event);
            }
        } else {
            $DB->delete_records('event', array('modulename'=>'assign', 'instance'=>$this->get_instance()->id));
        }
    }


    /**
     * Update this instance in the database
     *
     * @param stdClass $formdata - the data submitted from the form
     * @return bool false if an error occurs
     */
    public function update_instance($formdata) {
        global $DB;

        $update = new stdClass();
        $update->id = $formdata->instance;
        $update->name = $formdata->name;
        $update->timemodified = time();
        $update->course = $formdata->course;
        $update->intro = $formdata->intro;
        $update->introformat = $formdata->introformat;
        $update->alwaysshowdescription = $formdata->alwaysshowdescription;
        $update->preventlatesubmissions = $formdata->preventlatesubmissions;
        $update->submissiondrafts = $formdata->submissiondrafts;
        $update->sendnotifications = $formdata->sendnotifications;
        $update->sendlatenotifications = $formdata->sendlatenotifications;
        $update->duedate = $formdata->duedate;
        $update->allowsubmissionsfromdate = $formdata->allowsubmissionsfromdate;
        $update->grade = $formdata->grade;

        $result = $DB->update_record('assign', $update);
        $this->instance = $DB->get_record('assign', array('id'=>$update->id), '*', MUST_EXIST);

        // load the assignment so the plugins have access to it

        // call save_settings hook for submission plugins
        foreach ($this->submissionplugins as $plugin) {
            if (!$this->update_plugin_instance($plugin, $formdata)) {
                print_error($plugin->get_error());
                return false;
            }
        }
        foreach ($this->feedbackplugins as $plugin) {
            if (!$this->update_plugin_instance($plugin, $formdata)) {
                print_error($plugin->get_error());
                return false;
            }
        }


        // update the database record


        // update all the calendar events
        $this->update_calendar($this->get_course_module()->id);

        $this->update_gradebook(false, $this->get_course_module()->id);

        $update = new stdClass();
        $update->id = $this->get_instance()->id;
        $update->nosubmissions = (!$this->is_any_submission_plugin_enabled()) ? 1: 0;
        $DB->update_record('assign', $update);





        return $result;
    }

    /**
     * add elements in grading plugin form
     *
     * @param mixed $grade stdClass|null
     * @param MoodleQuickForm $mform
     * @param stdClass $data
     * @return void
     */
    private function add_plugin_grade_elements($grade, MoodleQuickForm $mform, stdClass $data) {
        foreach ($this->feedbackplugins as $plugin) {
            if ($plugin->is_enabled() && $plugin->is_visible()) {
                $mform->addElement('header', 'header_' . $plugin->get_type(), $plugin->get_name());
                if (!$plugin->get_form_elements($grade, $mform, $data)) {
                    $mform->removeElement('header_' . $plugin->get_type());
                }
            }
        }
    }



    /**
     * Add one plugins settings to edit plugin form
     *
     * @param assign_plugin $plugin The plugin to add the settings from
     * @param MoodleQuickForm $mform The form to add the configuration settings to. This form is modified directly (not returned)
     * @return void
     */
    private function add_plugin_settings(assign_plugin $plugin, MoodleQuickForm $mform) {
        global $CFG;
        if ($plugin->is_visible()) {
            // enabled
            //tied disableIf rule to this select element
            $mform->addElement('selectyesno', $plugin->get_subtype() . '_' . $plugin->get_type() . '_enabled', $plugin->get_name());
            $mform->addHelpButton($plugin->get_subtype() . '_' . $plugin->get_type() . '_enabled', 'enabled', $plugin->get_subtype() . '_' . $plugin->get_type());


            $default = get_config($plugin->get_subtype() . '_' . $plugin->get_type(), 'default');
            if ($plugin->get_config('enabled') !== false) {
                $default = $plugin->is_enabled();
            }
            $mform->setDefault($plugin->get_subtype() . '_' . $plugin->get_type() . '_enabled', $default);

            $plugin->get_settings($mform);

        }

    }


    /**
     * Add settings to edit plugin form
     *
     * @param MoodleQuickForm $mform The form to add the configuration settings to. This form is modified directly (not returned)
     * @return void
     */
    public function add_all_plugin_settings(MoodleQuickForm $mform) {
        $mform->addElement('header', 'general', get_string('submissionsettings', 'assign'));

        foreach ($this->submissionplugins as $plugin) {
            $this->add_plugin_settings($plugin, $mform);

        }
        $mform->addElement('header', 'general', get_string('feedbacksettings', 'assign'));
        foreach ($this->feedbackplugins as $plugin) {
            $this->add_plugin_settings($plugin, $mform);
        }
    }

    /**
     * Allow each plugin an opportunity to update the defaultvalues
     * passed in to the settings form (needed to set up draft areas for
     * editor and filemanager elements)
     * @param array $defaultvalues
     */
    public function plugin_data_preprocessing(&$defaultvalues) {
        foreach ($this->submissionplugins as $plugin) {
            if ($plugin->is_visible()) {
                $plugin->data_preprocessing($defaultvalues);
            }
        }
        foreach ($this->feedbackplugins as $plugin) {
            if ($plugin->is_visible()) {
                $plugin->data_preprocessing($defaultvalues);
            }
        }
    }

    /**
     * Get the name of the current module.
     *
     * @return string the module name (Assignment)
     */
    protected function get_module_name() {
        if (isset(self::$modulename)) {
            return self::$modulename;
        }
        self::$modulename = get_string('modulename', 'assign');
        return self::$modulename;
    }

    /**
     * Get the plural name of the current module.
     *
     * @return string the module name plural (Assignments)
     */
    protected function get_module_name_plural() {
        if (isset(self::$modulenameplural)) {
            return self::$modulenameplural;
        }
        self::$modulenameplural = get_string('modulenameplural', 'assign');
        return self::$modulenameplural;
    }

    /**
     * Has this assignment been constructed from an instance?
     *
     * @return bool
     */
    public function has_instance() {
        return $this->instance || $this->get_course_module();
    }

    /**
     * Get the settings for the current instance of this assignment
     *
     * @return stdClass The settings
     */
    public function get_instance() {
        global $DB;
        if ($this->instance) {
            return $this->instance;
        }
        if ($this->get_course_module()) {
            $this->instance = $DB->get_record('assign', array('id' => $this->get_course_module()->instance), '*', MUST_EXIST);
        }
        if (!$this->instance) {
            throw new coding_exception('Improper use of the assignment class. Cannot load the assignment record.');
        }
        return $this->instance;
    }

    /**
     * Get the context of the current course
     * @return mixed context|null The course context
     */
    public function get_course_context() {
        if (!$this->context && !$this->course) {
            throw new coding_exception('Improper use of the assignment class. Cannot load the course context.');
        }
        if ($this->context) {
            return $this->context->get_course_context();
        } else {
            return context_course::instance($this->course->id);
        }
    }


    /**
     * Get the current course module
     *
     * @return mixed stdClass|null The course module
     */
    public function get_course_module() {
        if ($this->coursemodule) {
            return $this->coursemodule;
        }
        if (!$this->context) {
            return null;
        }

        if ($this->context->contextlevel == CONTEXT_MODULE) {
            $this->coursemodule = get_coursemodule_from_id('assign', $this->context->instanceid, 0, false, MUST_EXIST);
            return $this->coursemodule;
        }
        return null;
    }

    /**
     * Get context module
     *
     * @return context
     */
    public function get_context() {
        return $this->context;
    }

    /**
     * Get the current course
     * @return mixed stdClass|null The course
     */
    public function get_course() {
        global $DB;
        if ($this->course) {
            return $this->course;
        }

        if (!$this->context) {
            return null;
        }
        $this->course = $DB->get_record('course', array('id' => $this->get_course_context()->instanceid), '*', MUST_EXIST);
        return $this->course;
    }

    /**
     * Return a grade in user-friendly form, whether it's a scale or not
     *
     * @param mixed $grade int|null
     * @param boolean $editing Are we allowing changes to this grade?
     * @param int $userid The user id the grade belongs to
     * @param int $modified Timestamp from when the grade was last modified
     * @return string User-friendly representation of grade
     */
    public function display_grade($grade, $editing, $userid=0, $modified=0) {
        global $DB;

        static $scalegrades = array();

        if ($this->get_instance()->grade >= 0) {
            // Normal number
            if ($editing && $this->get_instance()->grade > 0) {
                if ($grade < 0) {
                    $displaygrade = '';
                } else {
                    $displaygrade = format_float($grade);
                }
                $o = '<input type="text" name="quickgrade_' . $userid . '" value="' . $displaygrade . '" size="6" maxlength="10" class="quickgrade"/>';
                $o .= '&nbsp;/&nbsp;' . format_float($this->get_instance()->grade,2);
                $o .= '<input type="hidden" name="grademodified_' . $userid . '" value="' . $modified . '"/>';
                return $o;
            } else {
                if ($grade == -1 || $grade === null) {
                    return '-';
                } else {
                    return format_float(($grade),2) .'&nbsp;/&nbsp;'. format_float($this->get_instance()->grade,2);
                }
            }

        } else {
            // Scale
            if (empty($this->cache['scale'])) {
                if ($scale = $DB->get_record('scale', array('id'=>-($this->get_instance()->grade)))) {
                    $this->cache['scale'] = make_menu_from_list($scale->scale);
                } else {
                    return '-';
                }
            }
            if ($editing) {
                $o = '<select name="quickgrade_' . $userid . '" class="quickgrade">';
                $o .= '<option value="-1">' . get_string('nograde') . '</option>';
                foreach ($this->cache['scale'] as $optionid => $option) {
                    $selected = '';
                    if ($grade == $optionid) {
                        $selected = 'selected="selected"';
                    }
                    $o .= '<option value="' . $optionid . '" ' . $selected . '>' . $option . '</option>';
                }
                $o .= '</select>';
                $o .= '<input type="hidden" name="grademodified_' . $userid . '" value="' . $modified . '"/>';
                return $o;
            } else {
                $scaleid = (int)$grade;
                if (isset($this->cache['scale'][$scaleid])) {
                    return $this->cache['scale'][$scaleid];
                }
                return '-';
            }
        }
    }

    /**
     * Load a list of users enrolled in the current course with the specified permission and group (0 for no group)
     *
     * @param int $currentgroup
     * @param bool $idsonly
     * @return array List of user records
     */
    public function list_participants($currentgroup, $idsonly) {
        if ($idsonly) {
            return get_enrolled_users($this->context, "mod/assign:submit", $currentgroup, 'u.id');
        } else {
            return get_enrolled_users($this->context, "mod/assign:submit", $currentgroup);
        }
    }

    /**
     * Load a count of users enrolled in the current course with the specified permission and group (0 for no group)
     *
     * @param int $currentgroup
     * @return int number of matching users
     */
    public function count_participants($currentgroup) {
        return count_enrolled_users($this->context, "mod/assign:submit", $currentgroup);
    }

    /**
     * Load a count of users enrolled in the current course with the specified permission and group (optional)
     *
     * @param string $status The submission status - should match one of the constants
     * @return int number of matching submissions
     */
    public function count_submissions_with_status($status) {
        global $DB;
        return $DB->count_records_sql("SELECT COUNT('x')
                                     FROM {assign_submission}
                                    WHERE assignment = ? AND
                                          status = ?", array($this->get_course_module()->instance, $status));
    }

    /**
     * Utility function to get the userid for every row in the grading table
     * so the order can be frozen while we iterate it
     *
     * @return array An array of userids
     */
    private function get_grading_userid_list(){
        $filter = get_user_preferences('assign_filter', '');
        $table = new assign_grading_table($this, 0, $filter, 0, false);

        $useridlist = $table->get_column_data('userid');

        return $useridlist;
    }


    /**
     * Utility function get the userid based on the row number of the grading table.
     * This takes into account any active filters on the table.
     *
     * @param int $num The row number of the user
     * @param bool $last This is set to true if this is the last user in the table
     * @return mixed The user id of the matching user or false if there was an error
     */
    private function get_userid_for_row($num, $last){
        if (!array_key_exists('userid_for_row', $this->cache)) {
            $this->cache['userid_for_row'] = array();
        }
        if (array_key_exists($num, $this->cache['userid_for_row'])) {
            list($userid, $last) = $this->cache['userid_for_row'][$num];
            return $userid;
        }

        $filter = get_user_preferences('assign_filter', '');
        $table = new assign_grading_table($this, 0, $filter, 0, false);

        $userid = $table->get_cell_data($num, 'userid', $last);

        $this->cache['userid_for_row'][$num] = array($userid, $last);
        return $userid;
    }

    /**
     * Return all assignment submissions by ENROLLED students (even empty)
     *
     * @param string $sort optional field names for the ORDER BY in the sql query
     * @param string $dir optional specifying the sort direction, defaults to DESC
     * @return array The submission objects indexed by id
     */
    private function get_all_submissions( $sort="", $dir="DESC") {
        global $CFG, $DB;

        if ($sort == "lastname" or $sort == "firstname") {
            $sort = "u.$sort $dir";
        } else if (empty($sort)) {
            $sort = "a.timemodified DESC";
        } else {
            $sort = "a.$sort $dir";
        }

        return $DB->get_records_sql("SELECT a.*
                                       FROM {assign_submission} a, {user} u
                                      WHERE u.id = a.userid
                                            AND a.assignment = ?
                                   ORDER BY $sort", array($this->get_instance()->id));

    }

    /**
     * Generate zip file from array of given files
     *
     * @param array $filesforzipping - array of files to pass into archive_to_pathname - this array is indexed by the final file name and each element in the array is an instance of a stored_file object
     * @return path of temp file - note this returned file does not have a .zip extension - it is a temp file.
     */
     private function pack_files($filesforzipping) {
         global $CFG;
         //create path for new zip file.
         $tempzip = tempnam($CFG->tempdir.'/', 'assignment_');
         //zip files
         $zipper = new zip_packer();
         if ($zipper->archive_to_pathname($filesforzipping, $tempzip)) {
             return $tempzip;
         }
         return false;
    }

    /**
     * Finds all assignment notifications that have yet to be mailed out, and mails them.
     *
     * Cron function to be run periodically according to the moodle cron
     *
     * @return bool
     */
    static function cron() {
        global $DB;

        // only ever send a max of one days worth of updates
        $yesterday = time() - (24 * 3600);
        $timenow   = time();

        // Collect all submissions from the past 24 hours that require mailing.
        $sql = "SELECT s.*, a.course, a.name, g.*, g.id as gradeid, g.timemodified as lastmodified
                 FROM {assign} a
                 JOIN {assign_grades} g ON g.assignment = a.id
            LEFT JOIN {assign_submission} s ON s.assignment = a.id AND s.userid = g.userid
                WHERE g.timemodified >= :yesterday AND
                      g.timemodified <= :today AND
                      g.mailed = 0";
        $params = array('yesterday' => $yesterday, 'today' => $timenow);
        $submissions = $DB->get_records_sql($sql, $params);

        if (empty($submissions)) {
            mtrace('done.');
            return true;
        }

        mtrace('Processing ' . count($submissions) . ' assignment submissions ...');

        // Preload courses we are going to need those.
        $courseids = array();
        foreach ($submissions as $submission) {
            $courseids[] = $submission->course;
        }
        // Filter out duplicates
        $courseids = array_unique($courseids);
        $ctxselect = context_helper::get_preload_record_columns_sql('ctx');
        list($courseidsql, $params) = $DB->get_in_or_equal($courseids, SQL_PARAMS_NAMED);
        $sql = "SELECT c.*, {$ctxselect}
                  FROM {course} c
             LEFT JOIN {context} ctx ON ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel
                 WHERE c.id {$courseidsql}";
        $params['contextlevel'] = CONTEXT_COURSE;
        $courses = $DB->get_records_sql($sql, $params);
        // Clean up... this could go on for a while.
        unset($courseids);
        unset($ctxselect);
        unset($courseidsql);
        unset($params);

        // Simple array we'll use for caching modules.
        $modcache = array();

        // Message students about new feedback
        foreach ($submissions as $submission) {

            mtrace("Processing assignment submission $submission->id ...");

            // do not cache user lookups - could be too many
            if (!$user = $DB->get_record("user", array("id"=>$submission->userid))) {
                mtrace("Could not find user $submission->userid");
                continue;
            }

            // use a cache to prevent the same DB queries happening over and over
            if (!array_key_exists($submission->course, $courses)) {
                mtrace("Could not find course $submission->course");
                continue;
            }
            $course = $courses[$submission->course];
            if (isset($course->ctxid)) {
                // Context has not yet been preloaded. Do so now.
                context_helper::preload_from_record($course);
            }

            // Override the language and timezone of the "current" user, so that
            // mail is customised for the receiver.
            cron_setup_user($user, $course);

            // context lookups are already cached
            $coursecontext = context_course::instance($course->id);
            if (!is_enrolled($coursecontext, $user->id)) {
                $courseshortname = format_string($course->shortname, true, array('context' => $coursecontext));
                mtrace(fullname($user)." not an active participant in " . $courseshortname);
                continue;
            }

            if (!$grader = $DB->get_record("user", array("id"=>$submission->grader))) {
                mtrace("Could not find grader $submission->grader");
                continue;
            }

            if (!array_key_exists($submission->assignment, $modcache)) {
                if (! $mod = get_coursemodule_from_instance("assign", $submission->assignment, $course->id)) {
                    mtrace("Could not find course module for assignment id $submission->assignment");
                    continue;
                }
                $modcache[$submission->assignment] = $mod;
            } else {
                $mod = $modcache[$submission->assignment];
            }
            // context lookups are already cached
            $contextmodule = context_module::instance($mod->id);

            if (!$mod->visible) {
                // Hold mail notification for hidden assignments until later
                continue;
            }

            // need to send this to the student
            $messagetype = 'feedbackavailable';
            $eventtype = 'assign_notification';
            $updatetime = $submission->lastmodified;
            $modulename = get_string('modulename', 'assign');
            self::send_assignment_notification($grader, $user, $messagetype, $eventtype, $updatetime, $mod, $contextmodule, $course, $modulename, $submission->name);

            $grade = new stdClass();
            $grade->id = $submission->gradeid;
            $grade->mailed = 1;
            $DB->update_record('assign_grades', $grade);

            mtrace('Done');
        }
        mtrace('Done processing ' . count($submissions) . ' assignment submissions');

        cron_setup_user();

        // Free up memory just to be sure
        unset($courses);
        unset($modcache);

        return true;
    }

    /**
     * Update a grade in the grade table for the assignment and in the gradebook
     *
     * @param stdClass $grade a grade record keyed on id
     * @return bool true for success
     */
    private function update_grade($grade) {
        global $DB;

        $grade->timemodified = time();

        if ($grade->grade && $grade->grade != -1) {
            if ($this->get_instance()->grade > 0) {
                if (!is_numeric($grade->grade)) {
                    return false;
                } else if ($grade->grade > $this->get_instance()->grade) {
                    return false;
                } else if ($grade->grade < 0) {
                    return false;
                }
            } else {
                // this is a scale
                if ($scale = $DB->get_record('scale', array('id' => -($this->get_instance()->grade)))) {
                    $scaleoptions = make_menu_from_list($scale->scale);
                    if (!array_key_exists((int) $grade->grade, $scaleoptions)) {
                        return false;
                    }
                }
            }
        }

        $result = $DB->update_record('assign_grades', $grade);
        if ($result) {
            $this->gradebook_item_update(null, $grade);
        }
        return $result;
    }

    /**
     * display the submission that is used by a plugin
     * Uses url parameters 'sid', 'gid' and 'plugin'
     * @param string $pluginsubtype
     * @return string
     */
    private function view_plugin_content($pluginsubtype) {
        global $USER;

        $o = '';

        $submissionid = optional_param('sid', 0, PARAM_INT);
        $gradeid = optional_param('gid', 0, PARAM_INT);
        $plugintype = required_param('plugin', PARAM_TEXT);
        $item = null;
        if ($pluginsubtype == 'assignsubmission') {
            $plugin = $this->get_submission_plugin_by_type($plugintype);
            if ($submissionid <= 0) {
                throw new coding_exception('Submission id should not be 0');
            }
            $item = $this->get_submission($submissionid);

            // permissions
            if ($item->userid != $USER->id) {
                require_capability('mod/assign:grade', $this->context);
            }
            $o .= $this->output->render(new assign_header($this->get_instance(),
                                                              $this->get_context(),
                                                              $this->show_intro(),
                                                              $this->get_course_module()->id,
                                                              $plugin->get_name()));
            $o .= $this->output->render(new assign_submission_plugin_submission($plugin,
                                                              $item,
                                                              assign_submission_plugin_submission::FULL,
                                                              $this->get_course_module()->id,
                                                              $this->get_return_action(),
                                                              $this->get_return_params()));

            $this->add_to_log('view submission', get_string('viewsubmissionforuser', 'assign', $item->userid));
        } else {
            $plugin = $this->get_feedback_plugin_by_type($plugintype);
            if ($gradeid <= 0) {
                throw new coding_exception('Grade id should not be 0');
            }
            $item = $this->get_grade($gradeid);
            // permissions
            if ($item->userid != $USER->id) {
                require_capability('mod/assign:grade', $this->context);
            }
            $o .= $this->output->render(new assign_header($this->get_instance(),
                                                              $this->get_context(),
                                                              $this->show_intro(),
                                                              $this->get_course_module()->id,
                                                              $plugin->get_name()));
            $o .= $this->output->render(new assign_feedback_plugin_feedback($plugin,
                                                              $item,
                                                              assign_feedback_plugin_feedback::FULL,
                                                              $this->get_course_module()->id,
                                                              $this->get_return_action(),
                                                              $this->get_return_params()));
            $this->add_to_log('view feedback', get_string('viewfeedbackforuser', 'assign', $item->userid));
        }


        $o .= $this->view_return_links();

        $o .= $this->view_footer();
        return $o;
    }

    /**
     * render the content in editor that is often used by plugin
     *
     * @param string $filearea
     * @param int  $submissionid
     * @param string $plugintype
     * @param string $editor
     * @param string $component
     * @return string
     */
    public function render_editor_content($filearea, $submissionid, $plugintype, $editor, $component) {
        global $CFG;

        $result = '';

        $plugin = $this->get_submission_plugin_by_type($plugintype);

        $text = $plugin->get_editor_text($editor, $submissionid);
        $format = $plugin->get_editor_format($editor, $submissionid);

        $finaltext = file_rewrite_pluginfile_urls($text, 'pluginfile.php', $this->get_context()->id, $component, $filearea, $submissionid);
        $result .= format_text($finaltext, $format, array('overflowdiv' => true, 'context' => $this->get_context()));



        if ($CFG->enableportfolios) {
            require_once($CFG->libdir . '/portfoliolib.php');

            $button = new portfolio_add_button();
            $button->set_callback_options('assi…