Proyectos de Subversion Moodle

<?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/>.

namespace mod_quiz;

use coding_exception;

use context_module;

use core\output\inplace_editable;

use mod_quiz\event\quiz_grade_item_created;

use mod_quiz\event\quiz_grade_item_deleted;

use mod_quiz\event\quiz_grade_item_updated;

use mod_quiz\event\slot_grade_item_updated;

use mod_quiz\event\slot_mark_updated;

use mod_quiz\question\bank\qbank_helper;

use mod_quiz\question\qubaids_for_quiz;

use stdClass;

/**

 * Quiz structure class.

 *

 * The structure of the quiz. That is, which questions it is built up

 * from. This is used on the Edit quiz page (edit.php) and also when

 * starting an attempt at the quiz (startattempt.php). Once an attempt

 * has been started, then the attempt holds the specific set of questions

 * that that student should answer, and we no longer use this class.

 *

 * @package   mod_quiz

 * @copyright 2014 The Open University

 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class structure {

    /** @var quiz_settings the quiz this is the structure of. */

    protected $quizobj = null;

    /**

     * @var stdClass[] the questions in this quiz. Contains the row from the questions

     * table, with the data from the quiz_slots table added, and also question_categories.contextid.

     */

    protected $questions = [];

    /** @var stdClass[] quiz_slots.slot => the quiz_slots rows for this quiz, augmented by sectionid. */

    protected $slotsinorder = [];

    /**

     * @var stdClass[] this quiz's data from the quiz_sections table. Each item has a ->lastslot field too.

     */

    protected $sections = [];

    /** @var stdClass[] quiz_grade_items for this quiz indexed by id. */

    protected array $gradeitems = [];

    /** @var bool caches the results of can_be_edited. */

    protected $canbeedited = null;

    /** @var bool caches the results of can_add_random_question. */

    protected $canaddrandom = null;

    /**

     * Create an instance of this class representing an empty quiz.

     *

     * @return structure

     */

    public static function create() {

        return new self();

    }

    /**

     * Create an instance of this class representing the structure of a given quiz.

     *

     * @param quiz_settings $quizobj the quiz.

     * @return structure

     */

    public static function create_for_quiz($quizobj) {

        $structure = self::create();

        $structure->quizobj = $quizobj;

        $structure->populate_structure();

        return $structure;

    }

    /**

     * Whether there are any questions in the quiz.

     *

     * @return bool true if there is at least one question in the quiz.

     */

    public function has_questions() {

        return !empty($this->questions);

    }

    /**

     * Get the number of questions in the quiz.

     *

     * @return int the number of questions in the quiz.

     */

    public function get_question_count() {

        return count($this->questions);

    }

    /**

     * Get the information about the question with this id.

     *

     * @param int $questionid The question id.

     * @return stdClass the data from the questions table, augmented with

     * question_category.contextid, and the quiz_slots data for the question in this quiz.

     */

    public function get_question_by_id($questionid) {

        return $this->questions[$questionid];

    }

    /**

     * Get the information about the question in a given slot.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return stdClass the data from the questions table, augmented with

     * question_category.contextid, and the quiz_slots data for the question in this quiz.

     */

    public function get_question_in_slot($slotnumber) {

        return $this->questions[$this->slotsinorder[$slotnumber]->questionid];

    }

    /**

     * Get the name of the question in a given slot.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return stdClass the data from the questions table, augmented with

     */

    public function get_question_name_in_slot($slotnumber) {

        return $this->questions[$this->slotsinorder[$slotnumber]->name];

    }

    /**

     * Get the displayed question number (or 'i') for a given slot.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return string the question number ot display for this slot.

     */

    public function get_displayed_number_for_slot($slotnumber) {

        $slot = $this->slotsinorder[$slotnumber];

        return $slot->displaynumber ?? $slot->defaultnumber;

    }

    /**

     * Check the question has a number that could be customised.

     *

     * @param int $slotnumber

     * @return bool

     */

    public function can_display_number_be_customised(int $slotnumber): bool {

        return $this->is_real_question($slotnumber) && !quiz_has_attempts($this->quizobj->get_quizid());

    }

    /**

     * Check whether the question number is customised.

     *

     * @param int $slotid

     * @return bool

     * @todo MDL-76612 Final deprecation in Moodle 4.6

     * @deprecated since 4.2. $slot->displayednumber is no longer used. If you need this,

     *      use isset(...->displaynumber), but this method was not used.

     */

    public function is_display_number_customised(int $slotid): bool {

        $slotobj = $this->get_slot_by_id($slotid);

        return isset($slotobj->displaynumber);

    }

    /**

     * Make slot display number in place editable api call.

     * @param int $slotid

     * @param \context $context

     * @return \core\output\inplace_editable

     */

    public function make_slot_display_number_in_place_editable(int $slotid, \context $context): \core\output\inplace_editable {

        $slot = $this->get_slot_by_id($slotid);

        $editable = has_capability('mod/quiz:manage', $context);

        // Get the current value.

        $value = $slot->displaynumber ?? $slot->defaultnumber;

        $displayvalue = s($value);

        return new inplace_editable('mod_quiz', 'slotdisplaynumber', $slotid,

                $editable, $displayvalue, $value,

                get_string('edit_slotdisplaynumber_hint', 'mod_quiz'),

                get_string('edit_slotdisplaynumber_label', 'mod_quiz', $displayvalue));

    }

    /**

     * Get the page a given slot is on.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return int the page number of the page that slot is on.

     */

    public function get_page_number_for_slot($slotnumber) {

        return $this->slotsinorder[$slotnumber]->page;

    }

    /**

     * Get the slot id of a given slot slot.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return int the page number of the page that slot is on.

     */

    public function get_slot_id_for_slot($slotnumber) {

        return $this->slotsinorder[$slotnumber]->id;

    }

    /**

     * Get the question type in a given slot.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return string the question type (e.g. multichoice).

     */

    public function get_question_type_for_slot($slotnumber) {

        return $this->questions[$this->slotsinorder[$slotnumber]->questionid]->qtype;

    }

    /**

     * Whether it would be possible, given the question types, etc. for the

     * question in the given slot to require that the previous question had been

     * answered before this one is displayed.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool can this question require the previous one.

     */

    public function can_question_depend_on_previous_slot($slotnumber) {

        return $slotnumber > 1 && $this->can_finish_during_the_attempt($slotnumber - 1);

    }

    /**

     * Whether it is possible for another question to depend on this one finishing.

     * Note that the answer is not exact, because of random questions, and sometimes

     * questions cannot be depended upon because of quiz options.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool can this question finish naturally during the attempt?

     */

    public function can_finish_during_the_attempt($slotnumber) {

        if ($this->quizobj->get_navigation_method() == QUIZ_NAVMETHOD_SEQ) {

            return false;

        }

        if ($this->slotsinorder[$slotnumber]->section->shufflequestions) {

            return false;

        }

        if (in_array($this->get_question_type_for_slot($slotnumber), ['random', 'missingtype'])) {

            return \question_engine::can_questions_finish_during_the_attempt(

                    $this->quizobj->get_quiz()->preferredbehaviour);

        }

        if (isset($this->slotsinorder[$slotnumber]->canfinish)) {

            return $this->slotsinorder[$slotnumber]->canfinish;

        }

        try {

            $quba = \question_engine::make_questions_usage_by_activity('mod_quiz', $this->quizobj->get_context());

            $tempslot = $quba->add_question(\question_bank::load_question(

                    $this->slotsinorder[$slotnumber]->questionid));

            $quba->set_preferred_behaviour($this->quizobj->get_quiz()->preferredbehaviour);

            $quba->start_all_questions();

            $this->slotsinorder[$slotnumber]->canfinish = $quba->can_question_finish_during_attempt($tempslot);

            return $this->slotsinorder[$slotnumber]->canfinish;

        } catch (\Exception $e) {

            // If the question fails to start, this should not block editing.

            return false;

        }

    }

    /**

     * Whether it would be possible, given the question types, etc. for the

     * question in the given slot to require that the previous question had been

     * answered before this one is displayed.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool can this question require the previous one.

     */

    public function is_question_dependent_on_previous_slot($slotnumber) {

        return $this->slotsinorder[$slotnumber]->requireprevious;

    }

    /**

     * Is a particular question in this attempt a real question, or something like a description.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether that question is a real question.

     */

    public function is_real_question($slotnumber) {

        return $this->get_question_in_slot($slotnumber)->length != 0;

    }

    /**

     * Does the current user have '...use' capability over the question(s) in a given slot?

     *

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool true if they have the required capability.

     */

    public function has_use_capability(int $slotnumber): bool {

        $slot = $this->slotsinorder[$slotnumber];

        if (is_numeric($slot->questionid)) {

            // Non-random question.

            return question_has_capability_on($this->get_question_by_id($slot->questionid), 'use');

        } else {

            // Random question.

            $context = \context::instance_by_id($slot->contextid);

            return has_capability('moodle/question:useall', $context);

        }

    }

    /**

     * Get the course id that the quiz belongs to.

     *

     * @return int the course.id for the quiz.

     */

    public function get_courseid() {

        return $this->quizobj->get_courseid();

    }

    /**

     * Get the course module id of the quiz.

     *

     * @return int the course_modules.id for the quiz.

     */

    public function get_cmid() {

        return $this->quizobj->get_cmid();

    }

    /**

     * Get the quiz context.

     *

     * @return context_module the context of the quiz that this is the structure of.

     */

    public function get_context(): context_module {

        return $this->quizobj->get_context();

    }

    /**

     * Get id of the quiz.

     *

     * @return int the quiz.id for the quiz.

     */

    public function get_quizid() {

        return $this->quizobj->get_quizid();

    }

    /**

     * Get the quiz object.

     *

     * @return stdClass the quiz settings row from the database.

     */

    public function get_quiz() {

        return $this->quizobj->get_quiz();

    }

    /**

     * Quizzes can only be repaginated if they have not been attempted, the

     * questions are not shuffled, and there are two or more questions.

     *

     * @return bool whether this quiz can be repaginated.

     */

    public function can_be_repaginated() {

        return $this->can_be_edited() && $this->get_question_count() >= 2;

    }

    /**

     * Quizzes can only be edited if they have not been attempted.

     *

     * @return bool whether the quiz can be edited.

     */

    public function can_be_edited() {

        if ($this->canbeedited === null) {

            $this->canbeedited = !quiz_has_attempts($this->quizobj->get_quizid());

        }

        return $this->canbeedited;

    }

    /**

     * This quiz can only be edited if they have not been attempted.

     * Throw an exception if this is not the case.

     */

    public function check_can_be_edited() {

        if (!$this->can_be_edited()) {

            $reportlink = quiz_attempt_summary_link_to_reports($this->get_quiz(),

                    $this->quizobj->get_cm(), $this->quizobj->get_context());

            throw new \moodle_exception('cannoteditafterattempts', 'quiz',

                    new \moodle_url('/mod/quiz/edit.php', ['cmid' => $this->get_cmid()]), $reportlink);

        }

    }

    /**

     * How many questions are allowed per page in the quiz.

     * This setting controls how frequently extra page-breaks should be inserted

     * automatically when questions are added to the quiz.

     *

     * @return int the number of questions that should be on each page of the

     * quiz by default.

     */

    public function get_questions_per_page() {

        return $this->quizobj->get_quiz()->questionsperpage;

    }

    /**

     * Get quiz slots.

     *

     * @return stdClass[] the slots in this quiz.

     */

    public function get_slots() {

        return array_column($this->slotsinorder, null, 'id');

    }

    /**

     * Is this slot the first one on its page?

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether this slot the first one on its page.

     */

    public function is_first_slot_on_page($slotnumber) {

        if ($slotnumber == 1) {

            return true;

        }

        return $this->slotsinorder[$slotnumber]->page != $this->slotsinorder[$slotnumber - 1]->page;

    }

    /**

     * Is this slot the last one on its page?

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether this slot the last one on its page.

     */

    public function is_last_slot_on_page($slotnumber) {

        if (!isset($this->slotsinorder[$slotnumber + 1])) {

            return true;

        }

        return $this->slotsinorder[$slotnumber]->page != $this->slotsinorder[$slotnumber + 1]->page;

    }

    /**

     * Is this slot the last one in its section?

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether this slot the last one on its section.

     */

    public function is_last_slot_in_section($slotnumber) {

        return $slotnumber == $this->slotsinorder[$slotnumber]->section->lastslot;

    }

    /**

     * Is this slot the only one in its section?

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether this slot the only one on its section.

     */

    public function is_only_slot_in_section($slotnumber) {

        return $this->slotsinorder[$slotnumber]->section->firstslot ==

                $this->slotsinorder[$slotnumber]->section->lastslot;

    }

    /**

     * Is this slot the last one in the quiz?

     *

     * @param int $slotnumber the index of the slot in question.

     * @return bool whether this slot the last one in the quiz.

     */

    public function is_last_slot_in_quiz($slotnumber) {

        end($this->slotsinorder);

        return $slotnumber == key($this->slotsinorder);

    }

    /**

     * Is this the first section in the quiz?

     *

     * @param stdClass $section the quiz_sections row.

     * @return bool whether this is first section in the quiz.

     */

    public function is_first_section($section) {

        return $section->firstslot == 1;

    }

    /**

     * Is this the last section in the quiz?

     *

     * @param stdClass $section the quiz_sections row.

     * @return bool whether this is first section in the quiz.

     */

    public function is_last_section($section) {

        return $section->id == end($this->sections)->id;

    }

    /**

     * Does this section only contain one slot?

     *

     * @param stdClass $section the quiz_sections row.

     * @return bool whether this section contains only one slot.

     */

    public function is_only_one_slot_in_section($section) {

        return $section->firstslot == $section->lastslot;

    }

    /**

     * Get the final slot in the quiz.

     *

     * @return stdClass the quiz_slots for the final slot in the quiz.

     */

    public function get_last_slot() {

        return end($this->slotsinorder);

    }

    /**

     * Get a slot by its id. Throws an exception if it is missing.

     *

     * @param int $slotid the slot id.

     * @return stdClass the requested quiz_slots row.

     */

    public function get_slot_by_id($slotid) {

        foreach ($this->slotsinorder as $slot) {

            if ($slot->id == $slotid) {

                return $slot;

            }

        }

        throw new coding_exception('The slot with id ' . $slotid .

                ' could not be found in the quiz with id ' . $this->get_quizid() . '.');

    }

    /**

     * Get a slot by its slot number. Throws an exception if it is missing.

     *

     * @param int $slotnumber The slot number

     * @return stdClass

     * @throws coding_exception

     */

    public function get_slot_by_number($slotnumber) {

        if (!array_key_exists($slotnumber, $this->slotsinorder)) {

            throw new coding_exception('The \'slotnumber\' could not be found.');

        }

        return $this->slotsinorder[$slotnumber];

    }

    /**

     * Check whether adding a section heading is possible

     *

     * @param int $pagenumber the number of the page.

     * @return boolean

     */

    public function can_add_section_heading($pagenumber) {

        // There is a default section heading on this page,

        // do not show adding new section heading in the Add menu.

        if ($pagenumber == 1) {

            return false;

        }

        // Get an array of firstslots.

        $firstslots = [];

        foreach ($this->sections as $section) {

            $firstslots[] = $section->firstslot;

        }

        foreach ($this->slotsinorder as $slot) {

            if ($slot->page == $pagenumber) {

                if (in_array($slot->slot, $firstslots)) {

                    return false;

                }

            }

        }

        // Do not show the adding section heading on the last add menu.

        if ($pagenumber == 0) {

            return false;

        }

        return true;

    }

    /**

     * Get all the slots in a section of the quiz.

     *

     * @param int $sectionid the section id.

     * @return int[] slot numbers.

     */

    public function get_slots_in_section($sectionid) {

        $slots = [];

        foreach ($this->slotsinorder as $slot) {

            if ($slot->section->id == $sectionid) {

                $slots[] = $slot->slot;

            }

        }

        return $slots;

    }

    /**

     * Get all the sections of the quiz.

     *

     * @return stdClass[] the sections in this quiz.

     */

    public function get_sections() {

        return $this->sections;

    }

    /**

     * Get a particular section by id.

     *

     * @return stdClass the section.

     */

    public function get_section_by_id($sectionid) {

        return $this->sections[$sectionid];

    }

    /**

     * Get the number of questions in the quiz.

     *

     * @return int the number of questions in the quiz.

     */

    public function get_section_count() {

        return count($this->sections);

    }

    /**

     * Get the overall quiz grade formatted for display.

     *

     * @return string the maximum grade for this quiz.

     */

    public function formatted_quiz_grade() {

        return quiz_format_grade($this->get_quiz(), $this->get_quiz()->grade);

    }

    /**

     * Get the maximum mark for a question, formatted for display.

     *

     * @param int $slotnumber the index of the slot in question.

     * @return string the maximum mark for the question in this slot.

     */

    public function formatted_question_grade($slotnumber) {

        return quiz_format_question_grade($this->get_quiz(), $this->slotsinorder[$slotnumber]->maxmark);

    }

    /**

     * Get the number of decimal places for displaying overall quiz grades or marks.

     *

     * @return int the number of decimal places.

     */

    public function get_decimal_places_for_grades() {

        return $this->get_quiz()->decimalpoints;

    }

    /**

     * Get the number of decimal places for displaying question marks.

     *

     * @return int the number of decimal places.

     */

    public function get_decimal_places_for_question_marks() {

        return quiz_get_grade_format($this->get_quiz());

    }

    /**

     * Get any warnings to show at the top of the edit page.

     * @return string[] array of strings.

     */

    public function get_edit_page_warnings() {

        $warnings = [];

        if (quiz_has_attempts($this->quizobj->get_quizid())) {

            $reviewlink = quiz_attempt_summary_link_to_reports($this->quizobj->get_quiz(),

                    $this->quizobj->get_cm(), $this->quizobj->get_context());

            $warnings[] = get_string('cannoteditafterattempts', 'quiz', $reviewlink);

        }

        return $warnings;

    }

    /**

     * Get the date information about the current state of the quiz.

     * @return string[] array of two strings. First a short summary, then a longer

     * explanation of the current state, e.g. for a tool-tip.

     */

    public function get_dates_summary() {

        $timenow = time();

        $quiz = $this->quizobj->get_quiz();

        // Exact open and close dates for the tool-tip.

        $dates = [];

        if ($quiz->timeopen > 0) {

            if ($timenow > $quiz->timeopen) {

                $dates[] = get_string('quizopenedon', 'quiz', userdate($quiz->timeopen));

            } else {

                $dates[] = get_string('quizwillopen', 'quiz', userdate($quiz->timeopen));

            }

        }

        if ($quiz->timeclose > 0) {

            if ($timenow > $quiz->timeclose) {

                $dates[] = get_string('quizclosed', 'quiz', userdate($quiz->timeclose));

            } else {

                $dates[] = get_string('quizcloseson', 'quiz', userdate($quiz->timeclose));

            }

        }

        if (empty($dates)) {

            $dates[] = get_string('alwaysavailable', 'quiz');

        }

        $explanation = implode(', ', $dates);

        // Brief summary on the page.

        if ($timenow < $quiz->timeopen) {

            $currentstatus = get_string('quizisclosedwillopen', 'quiz',

                    userdate($quiz->timeopen, get_string('strftimedatetimeshort', 'langconfig')));

        } else if ($quiz->timeclose && $timenow <= $quiz->timeclose) {

            $currentstatus = get_string('quizisopenwillclose', 'quiz',

                    userdate($quiz->timeclose, get_string('strftimedatetimeshort', 'langconfig')));

        } else if ($quiz->timeclose && $timenow > $quiz->timeclose) {

            $currentstatus = get_string('quizisclosed', 'quiz');

        } else {

            $currentstatus = get_string('quizisopen', 'quiz');

        }

        return [$currentstatus, $explanation];

    }

    /**

     * Set up this class with the structure for a given quiz.

     */

    protected function populate_structure() {

        global $DB;

        $this->populate_grade_items();

        $slots = qbank_helper::get_question_structure($this->quizobj->get_quizid(), $this->quizobj->get_context());

        $this->questions = [];

        $this->slotsinorder = [];

        foreach ($slots as $slotdata) {

            $this->questions[$slotdata->questionid] = $slotdata;

            $slot = clone($slotdata);

            $slot->quizid = $this->quizobj->get_quizid();

            $this->slotsinorder[$slot->slot] = $slot;

        }

        // Get quiz sections in ascending order of the firstslot.

        $this->sections = $DB->get_records('quiz_sections', ['quizid' => $this->quizobj->get_quizid()], 'firstslot');

        $this->populate_slots_with_sections();

        $this->populate_question_numbers();

    }

    /**

     * Load the information about the grade items for this quiz.

     */

    protected function populate_grade_items(): void {

        global $DB;

        $this->gradeitems = $DB->get_records('quiz_grade_items',

                ['quizid' => $this->get_quizid()], 'sortorder');

    }

    /**

     * Fill in the section ids for each slot.

     */

    public function populate_slots_with_sections() {

        $sections = array_values($this->sections);

        foreach ($sections as $i => $section) {

            if (isset($sections[$i + 1])) {

                $section->lastslot = $sections[$i + 1]->firstslot - 1;

            } else {

                $section->lastslot = count($this->slotsinorder);

            }

            for ($slot = $section->firstslot; $slot <= $section->lastslot; $slot += 1) {

                $this->slotsinorder[$slot]->section = $section;

            }

        }

    }

    /**

     * Number the questions.

     */

    protected function populate_question_numbers() {

        $number = 1;

        foreach ($this->slotsinorder as $slot) {

            $question = $this->questions[$slot->questionid];

            if ($question->length == 0) {

                $slot->displaynumber = null;

                $slot->defaultnumber = get_string('infoshort', 'quiz');

            } else {

                $slot->defaultnumber = $number;

            }

            if ($slot->displaynumber === '') {

                $slot->displaynumber = null;

            }

            $number += $question->length;

        }

    }

    /**

     * Get the version options to show on the 'Questions' page for a particular question.

     *

     * @param int $slotnumber which slot to get the choices for.

     * @return stdClass[] other versions of this question. Each object has fields versionid,

     *       version and selected. Array is returned most recent version first.

     */

    public function get_version_choices_for_slot(int $slotnumber): array {

        $slot = $this->get_slot_by_number($slotnumber);

        // Get all the versions which exist.

        $versions = qbank_helper::get_version_options($slot->questionid);

        $latestversion = reset($versions);

        // Format the choices for display.

        $versionoptions = [];

        foreach ($versions as $version) {

            $version->selected = $version->version === $slot->requestedversion;

            if ($version->version === $latestversion->version) {

                $version->versionvalue = get_string('questionversionlatest', 'quiz', $version->version);

            } else {

                $version->versionvalue = get_string('questionversion', 'quiz', $version->version);

            }

            $versionoptions[] = $version;

        }

        // Make a choice for 'Always latest'.

        $alwaysuselatest = new stdClass();

        $alwaysuselatest->versionid = 0;

        $alwaysuselatest->version = 0;

        $alwaysuselatest->versionvalue = get_string('alwayslatest', 'quiz');

        $alwaysuselatest->selected = $slot->requestedversion === null;

        array_unshift($versionoptions, $alwaysuselatest);

        return $versionoptions;

    }

    /**

     * Move a slot from its current location to a new location.

     *

     * After calling this method, this class will be in an invalid state, and

     * should be discarded if you want to manipulate the structure further.

     *

     * @param int $idmove id of slot to be moved

     * @param int $idmoveafter id of slot to come before slot being moved

     * @param int $page new page number of slot being moved

     */

    public function move_slot($idmove, $idmoveafter, $page) {

        global $DB;

        $this->check_can_be_edited();

        $movingslot = $this->get_slot_by_id($idmove);

        if (empty($movingslot)) {

            throw new \moodle_exception('Bad slot ID ' . $idmove);

        }

        $movingslotnumber = (int) $movingslot->slot;

        // Empty target slot means move slot to first.

        if (empty($idmoveafter)) {

            $moveafterslotnumber = 0;

        } else {

            $moveafterslotnumber = (int) $this->get_slot_by_id($idmoveafter)->slot;

        }

        // If the action came in as moving a slot to itself, normalise this to

        // moving the slot to after the previous slot.

        if ($moveafterslotnumber == $movingslotnumber) {

            $moveafterslotnumber = $moveafterslotnumber - 1;

        }

        $followingslotnumber = $moveafterslotnumber + 1;

        // Prevent checking against non-existence slot when already at the last slot.

        if ($followingslotnumber == $movingslotnumber && !$this->is_last_slot_in_quiz($followingslotnumber)) {

            $followingslotnumber += 1;

        }

        // Check the target page number is OK.

        if ($page == 0 || $page === '') {

            $page = 1;

        }

        if (($moveafterslotnumber > 0 && $page < $this->get_page_number_for_slot($moveafterslotnumber)) ||

                $page < 1) {

            throw new coding_exception('The target page number is too small.');

        } else if (!$this->is_last_slot_in_quiz($moveafterslotnumber) &&

                $page > $this->get_page_number_for_slot($followingslotnumber)) {

            throw new coding_exception('The target page number is too large.');

        }

        // Work out how things are being moved.

        $slotreorder = [];

        if ($moveafterslotnumber > $movingslotnumber) {

            // Moving down.

            $slotreorder[$movingslotnumber] = $moveafterslotnumber;

            for ($i = $movingslotnumber; $i < $moveafterslotnumber; $i++) {

                $slotreorder[$i + 1] = $i;

            }

            $headingmoveafter = $movingslotnumber;

            if ($this->is_last_slot_in_quiz($moveafterslotnumber) ||

                    $page == $this->get_page_number_for_slot($moveafterslotnumber + 1)) {

                // We are moving to the start of a section, so that heading needs

                // to be included in the ones that move up.

                $headingmovebefore = $moveafterslotnumber + 1;

            } else {

                $headingmovebefore = $moveafterslotnumber;

            }

            $headingmovedirection = -1;

        } else if ($moveafterslotnumber < $movingslotnumber - 1) {

            // Moving up.

            $slotreorder[$movingslotnumber] = $moveafterslotnumber + 1;

            for ($i = $moveafterslotnumber + 1; $i < $movingslotnumber; $i++) {

                $slotreorder[$i] = $i + 1;

            }

            if ($page == $this->get_page_number_for_slot($moveafterslotnumber + 1)) {

                // Moving to the start of a section, don't move that section.

                $headingmoveafter = $moveafterslotnumber + 1;

            } else {

                // Moving tot the end of the previous section, so move the heading down too.

                $headingmoveafter = $moveafterslotnumber;

            }

            $headingmovebefore = $movingslotnumber + 1;

            $headingmovedirection = 1;

        } else {

            // Staying in the same place, but possibly changing page/section.

            if ($page > $movingslot->page) {

                $headingmoveafter = $movingslotnumber;

                $headingmovebefore = $movingslotnumber + 2;

                $headingmovedirection = -1;

            } else if ($page < $movingslot->page) {

                $headingmoveafter = $movingslotnumber - 1;

                $headingmovebefore = $movingslotnumber + 1;

                $headingmovedirection = 1;

            } else {

                return; // Nothing to do.

            }

        }

        if ($this->is_only_slot_in_section($movingslotnumber)) {

            throw new coding_exception('You cannot remove the last slot in a section.');

        }

        $trans = $DB->start_delegated_transaction();

        // Slot has moved record new order.

        if ($slotreorder) {

            update_field_with_unique_index('quiz_slots', 'slot', $slotreorder,

                    ['quizid' => $this->get_quizid()]);

        }

        // Page has changed. Record it.

        if ($movingslot->page != $page) {

            $DB->set_field('quiz_slots', 'page', $page,

                    ['id' => $movingslot->id]);

        }

        // Update section fist slots.

        quiz_update_section_firstslots($this->get_quizid(), $headingmovedirection,

                $headingmoveafter, $headingmovebefore);

        // If any pages are now empty, remove them.

        $emptypages = $DB->get_fieldset_sql("

                SELECT DISTINCT page - 1

                  FROM {quiz_slots} slot

                 WHERE quizid = ?

                   AND page > 1

                   AND NOT EXISTS (SELECT 1 FROM {quiz_slots} WHERE quizid = ? AND page = slot.page - 1)

              ORDER BY page - 1 DESC

                ", [$this->get_quizid(), $this->get_quizid()]);

        foreach ($emptypages as $emptypage) {

            $DB->execute("

                    UPDATE {quiz_slots}

                       SET page = page - 1

                     WHERE quizid = ?

                       AND page > ?

                    ", [$this->get_quizid(), $emptypage]);

        }

        $trans->allow_commit();

        // Log slot moved event.

        $event = \mod_quiz\event\slot_moved::create([

            'context' => $this->quizobj->get_context(),

            'objectid' => $idmove,

            'other' => [

                'quizid' => $this->quizobj->get_quizid(),

                'previousslotnumber' => $movingslotnumber,

                'afterslotnumber' => $moveafterslotnumber,

                'page' => $page

             ]

        ]);

        $event->trigger();

    }

    /**

     * Refresh page numbering of quiz slots.

     * @param stdClass[] $slots (optional) array of slot objects.

     * @return stdClass[] array of slot objects.

     */

    public function refresh_page_numbers($slots = []) {

        global $DB;