Initial commit

classes/completion/custom_completion.php

+<?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/>.
+
+/**
+ * Activity custom completion subclass for the adaptive quiz activity.
+ *
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\completion;
+
+use core_completion\activity_custom_completion;
+use mod_adaptivequiz\local\attempt;
+
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * @inheritDoc
+     */
+    public function get_state(string $rule): int {
+        $this->validate_rule($rule);
+
+        return attempt::user_has_completed_on_quiz($this->cm->instance, $this->userid)
+            ? COMPLETION_COMPLETE
+            : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionattemptcompleted'];
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function get_custom_rule_descriptions(): array {
+        return ['completionattemptcompleted' => get_string('completionattemptcompletedcminfo', 'adaptivequiz')];
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function get_sort_order(): array {
+        return ['completionview', 'completionusegrade', 'completionattemptcompleted'];
+    }
+}

classes/event/attempt_completed.php

+<?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/>.
+
+/**
+ * Event which is triggered when a user completes an attempt on adaptive quiz.
+ *
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\event;
+
+use core\event\base;
+use moodle_exception;
+use moodle_url;
+
+class attempt_completed extends base {
+
+    /**
+     * @inheritDoc
+     */
+    public static function get_name() {
+        return get_string('eventattemptcompleted', 'adaptivequiz');
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function get_description() {
+        return "The user with id '$this->userid' has completed the attempt with id '$this->objectid' for the " .
+            "adaptive quiz with course module id '$this->contextinstanceid'.";
+    }
+
+    /**
+     * Returns related URL where result of the event can be observed.
+     *
+     * @throws moodle_exception
+     * @return moodle_url
+     */
+    public function get_url() {
+        return new moodle_url('/mod/adaptivequiz/reviewattempt.php', ['attempt' => $this->objectid]);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public static function get_objectid_mapping() {
+        return ['db' => 'adaptivequiz_attempt', 'restore' => 'adaptiveattempts'];
+    }
+
+    /**
+     * @inheritDoc
+     */
+    protected function init() {
+        $this->data['objecttable'] = 'adaptivequiz_attempt';
+        $this->data['crud'] = 'u';
+        $this->data['edulevel'] = self::LEVEL_PARTICIPATING;
+    }
+}

classes/event/course_module_instance_list_viewed.php

+<?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/>.
+
+/**
+ * The mod_peerassess instance list viewed event.
+ *
+ * @copyright  2013 onwards Remote-Learner {@link http://www.remote-learner.ca/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\event;
+
+class course_module_instance_list_viewed extends \core\event\course_module_instance_list_viewed {
+    /**
+     * Create the event from course record.
+     *
+     * @param \stdClass $course
+     * @return course_module_instance_list_viewed
+     */
+    public static function create_from_course(\stdClass $course) {
+        $params = array(
+            'context' => \context_course::instance($course->id)
+        );
+        $event = self::create($params);
+        $event->add_record_snapshot('course', $course);
+        return $event;
+    }
+}

classes/event/course_module_viewed.php

+<?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/>.
+
+/**
+ * Defines the course module viewed event.
+ *
+ * @copyright  2013 onwards Remote-Learner {@link http://www.remote-learner.ca/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\event;
+
+class course_module_viewed extends \core\event\course_module_viewed {
+
+    protected function init() {
+        $this->data['objecttable'] = 'adaptivequiz';
+        parent::init();
+    }
+}

classes/form/requiredpassword.php

+<?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/>.
+
+/**
+ * Adaptivequiz required password form
+ *
+ * @copyright  2013 onwards Remote-Learner {@link http://www.remote-learner.ca/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\form;
+
+defined('MOODLE_INTERNAL') || die();
+
+require_once($CFG->libdir.'/formslib.php');
+
+use moodleform;
+use html_writer;
+
+class requiredpassword extends moodleform {
+    /** @var string $passwordmessage a string containing text for a failed password attempt */
+    public $passwordmessage = '';
+    /**
+     * This method is refactored code from the quiz's password rule add_preflight_check_form_fields() method.
+     * It prints a form for the user to enter a password
+     */
+    protected function definition() {
+        $mform = $this->_form;
+
+        foreach ($this->_customdata['hidden'] as $name => $value) {
+            if ($name === 'sesskey') {
+                continue;
+            }
+            if ($name === 'cmid' || $name === 'uniqueid') {
+                $mform->setType($name, PARAM_INT);
+            }
+            $mform->addElement('hidden', $name, $value);
+        }
+
+        $mform->addElement('header', 'passwordheader', get_string('password'));
+        $mform->addElement('static', 'passwordmessage', '', get_string('requirepasswordmessage', 'adaptivequiz'));
+
+        $attr = array('style' => 'color:red;', 'class' => 'wrongpassword');
+        $html = html_writer::start_tag('div', $attr);
+        $mform->addElement('html', $html);
+        $mform->addElement('static', 'message');
+        $html = html_writer::end_tag('div');
+        $mform->addElement('html', $html);
+
+        // Don't use the 'proper' field name of 'password' since that get's
+        // Firefox's password auto-complete over-excited.
+        $mform->addElement('password', 'quizpassword', get_string('enterrequiredpassword', 'adaptivequiz'));
+
+        $this->add_action_buttons(true, get_string('continue'));
+    }
+}

classes/local/attempt/attempt_state.php

+<?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/>.
+
+/**
+ * A class to emulate enum type for attempt state.
+ *
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_adaptivequiz\local\attempt;
+
+final class attempt_state {
+
+    public const IN_PROGRESS = 'inprogress';
+
+    public const COMPLETED = 'complete';
+
+    /**
+     * @var string $stateasstring
+     */
+    private $stateasstring;
+
+    private function __construct(string $state) {
+        $this->stateasstring = $state;
+    }
+
+    public function is_in_progress(): bool {
+        return self::IN_PROGRESS === $this->stateasstring;
+    }
+
+    public function is_completed(): bool {
+        return self::COMPLETED === $this->stateasstring;
+    }
+
+    public static function in_progress(): self {
+        return new self(self::IN_PROGRESS);
+    }
+
+    public static function completed(): self {
+        return new self(self::COMPLETED);
+    }
+}

classes/local/fetchquestion.php

+<?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 class does the work of fetching a questions associated with a level of difficulty and within
+ * a question category.
+ *
+ * @copyright  2013 onwards Remote-Learner {@link http://www.remote-learner.ca/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local;
+
+use coding_exception;
+use dml_exception;
+use dml_read_exception;
+use invalid_parameter_exception;
+use mod_adaptivequiz\local\repository\questions_number_per_difficulty;
+use mod_adaptivequiz\local\repository\questions_repository;
+use mod_adaptivequiz\local\repository\tags_repository;
+use moodle_exception;
+use stdClass;
+
+class fetchquestion {
+    /**
+     * The maximum number of attempts at finding a tag containing questions
+     */
+    const MAXTAGRETRY = 5;
+
+    /**
+     * The maximum number of tries at finding avaiable questions
+     */
+    const MAXNUMTRY = 100000;
+
+    /** @var stdClass $adaptivequiz object, properties come from the adaptivequiz table */
+    protected $adaptivequiz;
+
+    /**
+     * @var bool $debugenabled flag to denote developer debugging is enabled and this class should write message to the debug array
+     */
+    protected $debugenabled = false;
+
+    /** @var array $debug array containing debugging information */
+    protected $debug = array();
+
+    /** @var array $tags an array of tags that used to identify eligible questions for the attempt */
+    protected $tags = array();
+
+    /** @var int $level the level of difficutly that will be used to fetch questions */
+    protected $level = 1;
+
+    /** @var string $questcatids a string of comma separated question category ids */
+    protected $questcatids = '';
+
+    /** @var int $minimumlevel the minimum level achievable in the attempt */
+    protected $minimumlevel;
+
+    /** @var int $maximumlevel the maximum level achievable in the attempt */
+    protected $maximumlevel;
+
+    /**
+     * @var array $tagquestsum an array whose keys are difficulty numbers and values are the sum of questions associated with the
+     *      difficulty level
+     */
+    protected $tagquestsum = array();
+
+    /** @var bool $rebuild a flag used to force the rebuilding of the $tagquestsum property */
+    public $rebuild = false;
+
+    /**
+     * The constructor.
+     *
+     * @param stdClass $adaptivequiz A record object from {adaptivequiz}.
+     * @param int $level Level of difficulty to look for when fetching a question.
+     * @param int $minimumlevel The minimum level the student can achieve.
+     * @param int $maximumlevel The maximum level the student can achieve.
+     * @param array $tags An array of accepted tags.
+     * @throws coding_exception
+     */
+    public function __construct($adaptivequiz, $level, $minimumlevel, $maximumlevel, $tags = []) {
+        global $SESSION;
+
+        $this->adaptivequiz = $adaptivequiz;
+        $this->tags = $tags;
+        $this->tags[] = ADAPTIVEQUIZ_QUESTION_TAG;
+        $this->minimumlevel = $minimumlevel;
+        $this->maximumlevel = $maximumlevel;
+
+        if (!is_int($level) || 0 >= $level) {
+            throw new coding_exception('Argument 2 is not an positive integer', 'Second parameter must be a positive integer');
+        }
+
+        if ($minimumlevel >= $maximumlevel) {
+            throw new coding_exception('Minimum level is greater than maximum level',
+                'Invalid minimum and maximum parameters passed');
+        }
+
+        $this->level = $level;
+
+        // Initialize $tagquestsum property.
+        if (!isset($SESSION->adpqtagquestsum)) {
+            $SESSION->adpqtagquestsum = array();
+            $this->tagquestsum = $SESSION->adpqtagquestsum;
+        } else {
+            $this->tagquestsum = $SESSION->adpqtagquestsum;
+        }
+
+        if (debugging('', DEBUG_DEVELOPER)) {
+            $this->debugenabled = true;
+        }
+    }
+
+    /**
+     * This function sets the level of difficulty property
+     * @param int $level level of difficulty
+     * @return void
+     */
+    public function set_level($level = 1) {
+        if (!is_int($level) || 0 >= $level) {
+            throw new coding_exception('Argument 1 is not an positive integer', 'First parameter must be a positive integer');
+        }
+
+        $this->level = $level;
+    }
+
+    /**
+     * This function returns the level of difficulty property
+     * @return int - level of difficulty
+     */
+    public function get_level() {
+        return $this->level;
+    }
+
+    /**
+     * Reset the maximum question level to search for to a new value
+     *
+     * @param int $maximumlevel
+     * @return void
+     * @throws coding_exception if the maximum level is less than minimum level
+     */
+    public function set_maximum_level($maximumlevel) {
+        if ($maximumlevel < $this->minimumlevel) {
+            throw new coding_exception('Maximum level is less than minimum level', 'Invalid maximum level set.');
+        }
+        $this->maximumlevel = $maximumlevel;
+    }
+
+    /**
+     * Reset the maximum question level to search for to a new value
+     *
+     * @param int $maximumlevel
+     * @return void
+     * @throws coding_exception if the minimum level is less than maximum level
+     */
+    public function set_minimum_level($minimumlevel) {
+        if ($minimumlevel > $this->maximumlevel) {
+            throw new coding_exception('Minimum level is less than maximum level', 'Invalid minimum level set.');
+        }
+        $this->minimumlevel = $minimumlevel;
+    }
+
+    /**
+     * This functions adds a message to the debugging array
+     * @param string $message: details of the debugging message
+     * @return void
+     */
+    protected function print_debug($message = '') {
+        if ($this->debugenabled) {
+            $this->debug[] = $message;
+        }
+    }
+
+    /**
+     * Answer a string view of a variable for debugging purposes
+     * @param mixed $variable
+     */
+    protected function vardump($variable) {
+        ob_start();
+        var_dump($variable);
+        return ob_get_clean();
+    }
+
+    /**
+     * This function returns the debug array
+     * @return array - array of debugging messages
+     */
+    public function get_debug() {
+        return $this->debug;
+    }
+
+    /**
+     * This functions returns the $tagquestsum class property
+     * @return array an array whose keys are difficulty levels and values are the sum of questions associated with the difficulty
+     */
+    public function get_tagquestsum() {
+        return $this->tagquestsum;
+    }
+
+    /**
+     * This functions sets the $tagquestsum class property
+     * @param array an array whose keys are difficulty levels and values are the sum of questions associated with the difficulty
+     */
+    public function set_tagquestsum($tagquestsum) {
+        $this->tagquestsum = $tagquestsum;
+    }
+
+    /**
+     * This function decrements 1 from the sum of questions in a difficulty level
+     * @param array $tagquestsum an array equal to the $tagquestsum property, where the key is the difficulty level and the value
+     *      is the total number of
+     * questions associated with it.  This parameter will be modified.
+     * @param int $level the difficulty level
+     * @return array an array whose keys are difficulty levels and values are the sum of questions associated with the difficulty
+     */
+    public function decrement_question_sum_from_difficulty($tagquestsum, $level) {
+        if (array_key_exists($level, $tagquestsum)) {
+            $tagquestsum[$level] -= 1;
+        }
+
+        return $tagquestsum;
+    }
+
+    /**
+     * This function first checks if the session variable already contains a mapping of difficulty levels and the number of
+     * questions associated with each level. Otherwise it constructos a mapping of difficulty levels and the number of questions
+     * in each difficulty level.
+     * @param array $tagquestsum an array equal to the $tagquestsum property, where the key is the difficulty level and the value
+     *      is the total number of
+     * questions associated with it. This parameter will be modified.
+     * @param array $tags an array of tags used by the activity
+     * @param int $min the minimum difficulty allowed for the attempt
+     * @param int $max the maximum difficulty allowed for the attempt
+     * @param bool $rebuild true to force the rebuilding the difficulty question count array, otherwise false.  Set to "true" only
+     *      for brand new attempts
+     * @return array an array whose keys are difficulty levels and values are the sum of questions associated with the difficulty
+     */
+    public function initalize_tags_with_quest_count($tagquestsum, $tags, $min, $max, $rebuild = false) {
+        global $SESSION;
+
+        // Check to see if the tagquestsum argument is initialized.
+        $count = count($tagquestsum);
+        if (empty($count) || !empty($rebuild)) {
+            $tagquestsum = array();
+            // Retrieve the question categories set for this activity.
+            $questcat = $this->retrieve_question_categories();
+            // Traverse through the array of configured tags used by the activity.
+            foreach ($tags as $tag) {
+                // Retrieve all of id for the configured tag.
+                $tagids = $this->retrieve_all_tag_ids($min, $max, $tag);
+                // Retrieve a count of all of the questions associated with each tag.
+                $difficultiesquestionsnumber = $this->retrieve_tags_with_question_count($tagids, $questcat);
+
+                // Traverse the $difficultiesquestionsnumber array and add the values with the values current in the
+                // $tagquestsum argument.
+                foreach ($difficultiesquestionsnumber as $questionsnumberperdifficulty) {
+                    $difflevel = $questionsnumberperdifficulty->difficulty();
+                    $totalquestindiff = $questionsnumberperdifficulty->questions_number();
+
+                    // If the array key exists, then add the sum to what is already in the array.
+                    if (array_key_exists($difflevel, $tagquestsum)) {
+                        $tagquestsum[$difflevel] += $totalquestindiff;
+                    } else {
+                        $tagquestsum[$difflevel] = $totalquestindiff;
+                    }
+                }
+            }
+        } else {
+            $tagquestsum = $SESSION->adpqtagquestsum;
+        }
+
+        return $tagquestsum;
+    }
+
+    /**
+     * This function retrieves a question associated with a Moodle tag level of difficulty.  If the search for the tag turns up
+     * empty the function tries to find another tag whose difficulty level is either higher or lower
+     * @param array $excquestids an array of question ids to exclude from the search
+     * @return array an array of question ids
+     */
+    public function fetch_questions($excquestids = array()) {
+        $questids = array();
+
+        // Initialize the difficulty tag question sum property for searching.
+        $this->tagquestsum = $this->initalize_tags_with_quest_count($this->tagquestsum, $this->tags, $this->minimumlevel,
+            $this->maximumlevel, $this->rebuild);
+
+        // If tagquestsum property ie empty then return with nothing.
+        if (empty($this->tagquestsum)) {
+            $this->print_debug('fetch_questions() - tagquestsum is empty');
+            return array();
+        }
+        // Check if the requested level has available questions.
+        if (array_key_exists($this->level, $this->tagquestsum) && 0 < $this->tagquestsum[$this->level]) {
+            $tagids = $this->retrieve_tag($this->level);
+            $questids = $this->find_questions_with_tags($tagids, $excquestids);
+            $this->print_debug('fetch_questions() - Requested level '.$this->level.' has available questions. '.
+                $this->tagquestsum[$this->level].' question remaining.');
+            return $questids;
+        }
+
+        // Look for a level that has avaialbe qustions.
+        $level = $this->level;
+        for ($i = 1; $i <= self::MAXNUMTRY; $i++) {
+            // Check if the offset level is now out of bounds and stop the loop.
+            if ($this->minimumlevel > $level - $i && $this->maximumlevel < $level + $i) {
+                $i += self::MAXNUMTRY + 1;
+                $this->print_debug('fetch_questions() - searching levels has gone out of bounds of the min and max levels. '.
+                    'No questions returned');
+                continue;
+            }
+
+            // First check a level higher than the originally requested level.
+            $newlevel = $level + $i;
+
+            /*
+             * If the level is within the boundries set for the attempt and the level exists and the count of question is greater
+             * than zero, retrieve the tag id and the questions available
+             */
+            $condition = $newlevel <= $this->maximumlevel && array_key_exists($newlevel, $this->tagquestsum)
+                && 0 < $this->tagquestsum[$newlevel];
+            if ($condition) {
+                $tagids = $this->retrieve_tag($newlevel);
+                $questids = $this->find_questions_with_tags($tagids, $excquestids);
+                $this->level = $newlevel;
+                $i += self::MAXNUMTRY + 1;
+                $this->print_debug('fetch_questions() - original level could not be found.  Returned a question from level '.
+                    $newlevel.' instead');
+                continue;
+            }
+
+            // Check a level lower than the originally requested level.
+            $newlevel = $level - $i;
+
+            /*
+             * If the level is within the boundries set for the attempt and the level exists and the count of question is greater
+             *  than zero, retrieve the tag id and thequestions available
+             */
+            $condition = $newlevel >= $this->minimumlevel && array_key_exists($newlevel, $this->tagquestsum)
+                && 0 < $this->tagquestsum[$newlevel];
+            if ($condition) {
+                $tagids = $this->retrieve_tag($newlevel);
+                $questids = $this->find_questions_with_tags($tagids, $excquestids);
+                $this->level = $newlevel;
+                $i += self::MAXNUMTRY + 1;
+                $this->print_debug('fetch_questions() - original level could not be found.  Returned a question from level '
+                    .$newlevel.' instead');
+                continue;
+            }
+        }
+
+        return $questids;
+    }
+
+    /**
+     * This function retrieves all the tag ids that can be used in this attempt.
+     *
+     * @param int $minimumlevel The minimum level the student can achieve.
+     * @param int $maximumlevel The maximum level the student can achieve.
+     * @param string $tagprefix The tag prefix used.
+     * @return array An array whose keys represent the difficulty level and values are tag ids.
+     * @throws coding_exception
+     * @throws dml_exception
+     * @throws moodle_exception
+     */
+    public function retrieve_all_tag_ids(int $minimumlevel, int $maximumlevel, string $tagprefix): array {
+        if (empty(trim($tagprefix))) {
+            throw new invalid_parameter_exception('Tag prefix cannot be empty.');
+        }
+
+        $tags = array_map(function(int $level): string {
+            return ADAPTIVEQUIZ_QUESTION_TAG . $level;
+        }, range($minimumlevel, $maximumlevel));
+
+        if (!$leveltagidmap = tags_repository::get_question_level_to_tag_id_mapping_by_tag_names($tags)) {
+            return [];
+        }
+
+        return $leveltagidmap;
+    }
+
+    /**
+     * This function determines how many questions are associated with a tag, for questions contained in the category
+     * used by the activity.
+     *
+     * @param array $tagids an array whose key is the difficulty level and value is the tag id representing the difficulty level
+     * @param array $categories an array whose key and value is the question category id
+     * @return questions_number_per_difficulty[]
+     * @throws coding_exception
+     * @throws dml_read_exception
+     * @throws dml_exception
+     */
+    public function retrieve_tags_with_question_count($tagids, $categories): array {
+        return questions_repository::count_questions_number_per_difficulty($tagids, $categories);
+    }
+
+    /**
+     * This function retrieves all tag ids, used by this activity and associated with a particular level of difficulty.
+     *
+     * @param int $level The level of difficulty (optional). If 0 is passed then the function will use the level class
+     * property, otherwise the argument value will be used.
+     * @return array An array whose keys represent the difficulty level and values are tag ids.
+     * @throws dml_exception
+     * @throws coding_exception
+     */
+    public function retrieve_tag(int $level = 0): array {
+        $tags = array_map(function(string $tag) use($level): string {
+            return $tag . $level;
+        }, $this->tags);
+
+        if (!$tagidlist = tags_repository::get_tag_id_list_by_tag_names($tags)) {
+            return [];
+        }
+
+        return $tagidlist;
+    }
+
+    /**
+     * This function retrieves questions within the assigned question categories and
+     * questions associated with tagids
+     * @param array $tagids an array of tag is
+     * @param array $exclude an array of question ids to exclude from the search
+     * @return array an array whose keys are qustion ids and values are the question names
+     */
+    public function find_questions_with_tags($tagids = [], $exclude = []) {
+        $questcat = $this->retrieve_question_categories();
+
+        return questions_repository::find_questions_with_tags($tagids, $questcat, $exclude);
+    }
+
+    /**
+     * This function retrieves all of the question categories used the activity.
+     * @return array an array of quesiton category ids
+     */
+    protected function retrieve_question_categories() {
+        global $DB;
+
+        // Check cached result.
+        if (!empty($this->questcatids)) {
+            $this->print_debug('retrieve_question_categories() - question category ids (from cache): '.
+                $this->vardump($this->questcatids));
+            return $this->questcatids;
+        }
+
+        $param = array('instance' => $this->adaptivequiz->id);
+        $records = $DB->get_records_menu('adaptivequiz_question', $param, 'questioncategory ASC', 'id,questioncategory');
+
+        // Cache the results.
+        $this->questcatids = $records;
+
+        $this->print_debug('retrieve_question_categories() - question category ids: '.$this->vardump($records));
+
+        return $records;
+    }
+
+    /**
+     * The destruct method saves the difficult level and qustion number mapping to the session variable
+     */
+    public function __destruct() {
+        global $SESSION;
+        $SESSION->adpqtagquestsum = $this->tagquestsum;
+    }
+}

classes/local/questionanalysis/attempt_score.php

+<?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 class provides access to various numeric representations of a score.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis;
+
+use mod_adaptivequiz\local\catalgo;
+
+class attempt_score {
+
+    /** @var float $measuredabilitylogits The measured ability of the attempt in logits. */
+    protected $measuredabilitylogits = null;
+
+    /** @var float $standarderrorlogits The standard error in the score in logits. */
+    protected $standarderrorlogits = null;
+
+    /** @var float $lowestlevel The lowest level of question in the adaptive quiz. */
+    protected $lowestlevel = null;
+
+    /** @var float $highestlevel The highest level of question in the adaptive quiz. */
+    protected $highestlevel = null;
+
+    /**
+     * Constructor
+     *
+     * @return void
+     */
+    public function __construct ($measuredabilitylogits, $standarderrorlogits, $lowestlevel, $highestlevel) {
+        $this->measuredabilitylogits = $measuredabilitylogits;
+        $this->standarderrorlogits = $standarderrorlogits;
+        $this->lowestlevel = $lowestlevel;
+        $this->highestlevel = $highestlevel;
+    }
+
+    /**
+     * Answer the measured ability in logits.
+     *
+     * @return float
+     */
+    public function measured_ability_in_logits () {
+        return $this->measuredabilitylogits;
+    }
+
+    /**
+     * Answer the standard error in logits.
+     *
+     * @return float
+     */
+    public function standard_error_in_logits () {
+        return $this->standarderrorlogits;
+    }
+
+    /**
+     * Answer the measured ability as a fraction 0-1.
+     *
+     * @return float
+     */
+    public function measured_ability_in_fraction () {
+        return catalgo::convert_logit_to_fraction($this->measuredabilitylogits);
+    }
+
+    /**
+     * Answer the standard error a fraction 0-0.5.
+     *
+     * @return float
+     */
+    public function standard_error_in_fraction () {
+        return catalgo::convert_logit_to_percent($this->standarderrorlogits);
+    }
+
+    /**
+     * Answer the measured ability on the adaptive quiz's scale
+     *
+     * @return float
+     */
+    public function measured_ability_in_scale () {
+        return catalgo::map_logit_to_scale($this->measuredabilitylogits, $this->highestlevel, $this->lowestlevel);
+    }
+
+    /**
+     * Answer the standard error on the adaptive quiz's scale
+     *
+     * @return float
+     */
+    public function standard_error_in_scale () {
+        return catalgo::convert_logit_to_percent($this->standarderrorlogits) * ($this->highestlevel - $this->lowestlevel);
+    }
+}

classes/local/questionanalysis/question_analyser.php

+<?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 class provides a mechanism for analysing the usage, performance, and efficacy
+ * of a single question in an adaptive quiz.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis;
+
+use context;
+use InvalidArgumentException;
+use mod_adaptivequiz\local\catalgo;
+use mod_adaptivequiz\local\questionanalysis\statistics\question_statistic;
+use mod_adaptivequiz\local\questionanalysis\statistics\question_statistic_result;
+use question_definition;
+use stdClass;
+
+class question_analyser {
+
+    /** @var context the context this usage belongs to. */
+    protected $context;
+
+    /** @var question_definition $definition The question  */
+    protected $definition = null;
+
+    /** @var float $level The question level */
+    protected $level = null;
+
+    /** @var float $lowestlevel The lowest question-level in the adaptive quiz */
+    protected $lowestlevel = null;
+
+    /** @var float $highestlevel The highest question-level in the adaptive quiz */
+    protected $highestlevel = null;
+
+    /** @var array $results An array of the re objects */
+    protected $results = array();
+
+    /** @var array $statistics An array of the adaptivequiz_question_statistic added to this report */
+    protected $statistics = array();
+
+    /** @var array $statisticresults An array of the adaptivequiz_question_statistic_result added to this report */
+    protected $statisticresults = array();
+
+    /**
+     * Constructor - Create a new analyser.
+     *
+     * @param object $context
+     * @param question_definition $definition
+     * @param float $level The level (0-1) of the question.
+     * @return void
+     */
+    public function __construct ($context, question_definition $definition, $level, $lowestlevel, $highestlevel) {
+        $this->context = $context;
+        $this->definition = $definition;
+        $this->level = $level;
+        $this->lowestlevel = $lowestlevel;
+        $this->highestlevel = $highestlevel;
+    }
+
+    /**
+     * Add an usage result for this question.
+     *
+     * @param attempt_score $score The user's score on this attempt.
+     * @param boolean $correct True if the user answered correctly.
+     * @param string $answer
+     * @return void
+     */
+    public function add_result ($attemptid, $user, attempt_score $score, $correct, $answer) {
+        $result = new stdClass();
+        $result->attemptid = $attemptid;
+        $result->user = $user;
+        $result->score = $score;
+        $result->correct = $correct;
+        $result->answer = $answer;
+        $this->results[] = $result;
+    }
+
+    /**
+     * @return context the context this usage belongs to.
+     */
+    public function get_owning_context() {
+        return $this->context;
+    }
+
+    /**
+     * Answer the question definition for this question.
+     *
+     * @return question_definition
+     */
+    public function get_question_definition () {
+        return $this->definition;
+    }
+
+    /**
+     * Answer the question level for this question.
+     *
+     * @return int
+     */
+    public function get_question_level () {
+        return $this->level;
+    }
+
+    /**
+     * Answer the question level for this question in logits.
+     *
+     * @return int
+     */
+    public function get_question_level_in_logits () {
+        return catalgo::convert_linear_to_logit($this->level, $this->lowestlevel, $this->highestlevel);
+    }
+
+    /**
+     * Answer the results for this question
+     *
+     * @return array An array of stdClass objects.
+     */
+    public function get_results () {
+        return $this->results;
+    }
+
+    /**
+     * Add and calculate a statistic.
+     *
+     * @param string $key A key to identify this statistic for sorting and printing.
+     * @param question_statistic $statistic
+     * @return void
+     */
+    public function add_statistic ($key, question_statistic $statistic) {
+        if (!empty($this->statistics[$key])) {
+            throw new InvalidArgumentException("Statistic key '$key' is already in use.");
+        }
+        $this->statistics[$key] = $statistic;
+        $this->statisticresults[$key] = $statistic->calculate($this);
+    }
+
+    /**
+     * Answer a statistic result.
+     *
+     * @param string $key A key to identify this statistic.
+     * @return question_statistic_result
+     */
+    public function get_statistic_result ($key) {
+        if (empty($this->statisticresults[$key])) {
+            throw new InvalidArgumentException("Unknown statistic key '$key'.");
+        }
+        return $this->statisticresults[$key];
+    }
+
+    /**
+     * Utility function to map a logit value to this question's scale
+     *
+     * @param $logit
+     * @return float Scaled value
+     */
+    public function map_logit_to_scale ($logit) {
+        return catalgo::map_logit_to_scale($logit, $this->highestlevel, $this->lowestlevel);
+    }
+}

classes/local/questionanalysis/question_result.php

+<?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 class stores information about a particular attempt's result on a question
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis;
+
+use Exception;
+use InvalidArgumentException;
+
+class question_result {
+
+    /** @var float $_measuredability The measured ability of the user who attempted this question */
+    protected $_measuredability = null;
+
+    /** @var boolean $_correct True if the user was correct in their answer */
+    protected $_correct = null;
+
+    /**
+     * Constructor - Create a new result.
+     *
+     * @param float $measuredability The measured ability (0-1) of the user in this attempt.
+     * @param boolean $correct
+     * @return void
+     */
+    public function __construct ($measuredability, $correct) {
+        if (!is_numeric($measuredability) || $measuredability < 0 || $measuredability > 1) {
+            throw new InvalidArgumentException('$measuredability must be a float between 0 and 1.');
+        }
+        $this->_measuredability = $measuredability;
+        $this->_correct = (bool)$correct;
+    }
+
+    /**
+     * Magic method to provide read-only access to our parameters
+     *
+     * @param $key
+     * @return mixed
+     */
+    public function __get ($key) {
+        $param = '$_'.$key;
+        if (isset($this->$param)) {
+            return $this->$param;
+        } else {
+            throw new Exception('Unknown property, '.get_class($this).'->'.$key.'.');
+        }
+    }
+}

classes/local/questionanalysis/quiz_analyser.php

+<?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_adaptivequiz\local\questionanalysis;
+
+defined('MOODLE_INTERNAL') || die();
+
+require_once($CFG->dirroot.'/tag/lib.php');
+
+use core_tag_tag;
+use Exception;
+use InvalidArgumentException;
+use mod_adaptivequiz\local\attempt\attempt_state;
+use mod_adaptivequiz\local\questionanalysis\statistics\question_statistic;
+use question_engine;
+use stdClass;
+
+/**
+ * Questions-analyser class.
+ *
+ * The class provides a mechanism for loading and analysing question usage, performance, and efficacy.
+ *
+ * @package    mod_adaptivequiz
+ * @copyright  2013 Remote-Learner {@link http://www.remote-learner.ca/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class quiz_analyser {
+
+    /** @var array $questions An array of all questions loaded and their stats */
+    protected $questions = array();
+
+    /** @var array $statistics An array of the statistics added to this report */
+    protected $statistics = array();
+
+    /**
+     * Constructor - Create a new analyser.
+     *
+     * @return void
+     */
+    public function __construct() {
+
+    }
+
+    /**
+     * Load attempts from an adaptive quiz instance.
+     *
+     * @param int $instance
+     */
+    public function load_attempts(int $instance): void {
+        global $DB;
+
+        $adaptivequiz  = $DB->get_record('adaptivequiz', ['id' => $instance], '*');
+
+        // Get all of the completed attempts for this adaptive quiz instance.
+        $attempts  = $DB->get_records('adaptivequiz_attempt',
+            ['instance' => $instance, 'attemptstate' => attempt_state::COMPLETED]);
+
+        foreach ($attempts as $attempt) {
+            if ($attempt->uniqueid == 0) {
+                continue;
+            }
+
+            $user = $DB->get_record('user', ['id' => $attempt->userid]);
+            if (!$user) {
+                $user = new stdClass();
+                $user->firstname = get_string('unknownuser', 'adaptivequiz');
+                $user->lastname = '#' . $attempt->userid;
+            }
+
+            // For each attempt, get the attempt's final score.
+            $score = new attempt_score($attempt->measure, $attempt->standarderror, $adaptivequiz->lowestlevel,
+                $adaptivequiz->highestlevel);
+
+            // For each attempt, loop through all questions asked and add that usage
+            // to the question.
+            $quba = question_engine::load_questions_usage_by_activity($attempt->uniqueid);
+            foreach ($quba->get_slots() as $i => $slot) {
+                $question = $quba->get_question($slot);
+
+                // Create a question-analyser for the question.
+                if (empty($this->questions[$question->id])) {
+                    $tags = core_tag_tag::get_item_tags_array('core_question', 'question', $question->id);
+                    $difficulty = adaptivequiz_get_difficulty_from_tags($tags);
+                    $this->questions[$question->id] = new question_analyser($quba->get_owning_context(), $question,
+                        $difficulty, $adaptivequiz->lowestlevel, $adaptivequiz->highestlevel);
+                }
+
+                // Record the attempt score and the individual question result.
+                // KNIGHT: Questions are considered correct if the marked fraction is at least at the acceptance threshold determined by the plugin settings
+                $correct = ($quba->get_question_fraction($slot) >= $adaptivequiz->acceptancethreshold);
+                $answer = $quba->get_response_summary($slot);
+                $this->questions[$question->id]->add_result($attempt->id, $user, $score, $correct, $answer);
+            }
+        }
+    }
+
+    /**
+     * Add a statistic to calculate.
+     *
+     * @param string $key A key to identify this statistic for sorting and printing.
+     * @param question_statistic $statistic
+     * @return void
+     */
+    public function add_statistic($key, question_statistic $statistic) {
+        if (!empty($this->statistics[$key])) {
+            throw new InvalidArgumentException("Statistic key '$key' is already in use.");
+        }
+        $this->statistics[$key] = $statistic;
+        foreach ($this->questions as $question) {
+            $question->add_statistic($key, $statistic);
+        }
+    }
+
+    /**
+     * Answer a header row.
+     *
+     * @return array
+     */
+    public function get_header() {
+        $header = array();
+        $header['id'] = get_string('id', 'adaptivequiz');
+        $header['name'] = get_string('adaptivequizname', 'adaptivequiz');
+        $header['level'] = get_string('attemptquestion_level', 'adaptivequiz');
+        foreach ($this->statistics as $key => $statistic) {
+            $header[$key] = $statistic->get_display_name();
+        }
+        return $header;
+    }
+
+    /**
+     * Return an array of table records, sorted by the statistics given.
+     *
+     * @param string $sort Which statistic to sort on.
+     * @param string $direction ASC or DESC.
+     * @return array
+     */
+    public function get_records($sort = null, $direction = 'ASC') {
+        if (empty($this->questions)) {
+            return [];
+        }
+
+        $records = [];
+        foreach ($this->questions as $question) {
+            $record = [];
+            $record[] = $question->get_question_definition()->id;
+            $record[] = $question->get_question_definition()->name;
+            $record[] = $question->get_question_level();
+            foreach ($this->statistics as $key => $statistic) {
+                $record[] = $question->get_statistic_result($key)->printable();
+            }
+            $records[] = $record;
+        }
+
+        if ($direction != 'ASC' && $direction != 'DESC') {
+            throw new InvalidArgumentException('Invalid sort direction. Must be SORT_ASC or SORT_DESC, \''.$direction.'\' given.');
+        }
+        if ($direction == 'DESC') {
+            $direction = SORT_DESC;
+        } else {
+            $direction = SORT_ASC;
+        }
+
+        if (!is_null($sort)) {
+            $sortkeys = [];
+            foreach ($this->questions as $question) {
+                if ($sort == 'name') {
+                    $sortkeys[] = $question->get_question_definition()->name;
+                    $sorttype = SORT_REGULAR;
+                } else if ($sort == 'level') {
+                    $sortkeys[] = $question->get_question_level();
+                    $sorttype = SORT_NUMERIC;
+                } else {
+                    $sortkeys[] = $question->get_statistic_result($sort)->sortable();
+                    $sorttype = SORT_NUMERIC;
+                }
+            }
+            array_multisort($sortkeys, $direction, $sorttype, $records);
+        }
+
+        return $records;
+    }
+
+    /**
+     * Answer a question-analyzer for a particular question id analyze
+     *
+     * @param int $qid The question id
+     * @return question_analyser
+     * @throws Exception
+     */
+    public function get_question_analyzer($qid) {
+        if (!isset($this->questions[$qid])) {
+            throw new Exception('Question-id not found.');
+        }
+        return $this->questions[$qid];
+    }
+
+    /**
+     * Answer the record for a single question
+     *
+     * @param int $qid The question id
+     * @return array
+     * @throws Exception
+     */
+    public function get_record($qid) {
+        $question = $this->get_question_analyzer($qid);
+        $record = [];
+        $record[] = $question->get_question_definition()->id;
+        $record[] = $question->get_question_definition()->name;
+        $record[] = $question->get_question_level();
+        foreach ($this->statistics as $key => $statistic) {
+            $record[] = $question->get_statistic_result($key)->printable();
+        }
+        return $record;
+    }
+}

classes/local/questionanalysis/statistics/answers_statistic.php

+<?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_adaptivequiz\local\questionanalysis\statistics;
+
+use html_writer;
+use mod_adaptivequiz\local\questionanalysis\question_analyser;
+use moodle_url;
+use stdClass;
+
+/**
+ * This interface defines the methods required for pluggable statistics that may be added to the question analysis.
+ *
+ * @package    mod_adaptivequiz
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class answers_statistic implements question_statistic {
+    /**
+     * Answer a display-name for this statistic.
+     *
+     * @return string
+     */
+    public function get_display_name () {
+        return get_string('answers_display_name', 'adaptivequiz');
+    }
+
+    /**
+     * Calculate this statistic for a question's results.
+     *
+     * @param question_analyser $analyser
+     * @return question_statistic_result
+     */
+    public function calculate(question_analyser $analyser): question_statistic_result {
+        // Sort the results.
+        $results = $analyser->get_results();
+        foreach ($results as $result) {
+            $sortkeys[] = $result->score->measured_ability_in_logits();
+        }
+        array_multisort($sortkeys, SORT_NUMERIC, SORT_DESC, $results);
+
+        // Sort the results into three arrays based on how far above or below the question-level the users are.
+        $high = array();
+        $mid = array();
+        $low = array();
+        foreach ($results as $result) {
+            $ceiling = $result->score->measured_ability_in_logits() + $result->score->standard_error_in_logits();
+            $floor = $result->score->measured_ability_in_logits() - $result->score->standard_error_in_logits();
+            if ($analyser->get_question_level_in_logits() < $floor) {
+                // User is significantly above the question-level.
+                $high[] = $result;
+            } else if ($analyser->get_question_level_in_logits() > $ceiling) {
+                // User is significantly below the question-level.
+                $low[] = $result;
+            } else {
+                // User's ability overlaps the question level.
+                $mid[] = $result;
+            }
+        }
+
+        ob_start();
+        print html_writer::end_tag('tr');
+        print html_writer::start_tag('tr');
+        print html_writer::tag('th', get_string('attemptquestion_ability', 'adaptivequiz'));
+        print html_writer::tag('th', get_string('user', 'adaptivequiz'));
+        print html_writer::tag('th', get_string('result', 'adaptivequiz'));
+        print html_writer::tag('th', get_string('answer', 'adaptivequiz'));
+        print html_writer::tag('th', '');
+        print html_writer::end_tag('tr');
+        $headings = ob_get_clean();
+
+        ob_start();
+        print html_writer::start_tag('table', array('class' => 'adpq_answers_table'));
+
+        print html_writer::start_tag('thead');
+        print html_writer::start_tag('tr');
+        print html_writer::tag('th', get_string('highlevelusers', 'adaptivequiz').':',
+            array('colspan' => '5', 'class' => 'section'));
+        print $headings;
+        print html_writer::end_tag('thead');
+
+        print html_writer::start_tag('tbody', array('class' => 'adpq_highlevel'));
+        if (count($high)) {
+            foreach ($high as $result) {
+                $this->print_user_result($result);
+            }
+        } else {
+            $this->print_empty_user_result();
+        }
+        print html_writer::end_tag('tbody');
+
+        print html_writer::start_tag('thead');
+        print html_writer::start_tag('tr');
+        print html_writer::tag('th', get_string('midlevelusers', 'adaptivequiz').':',
+            array('colspan' => '5', 'class' => 'section'));
+        print $headings;
+        print html_writer::end_tag('thead');
+
+        print html_writer::start_tag('tbody', array('class' => 'adpq_midlevel'));
+        if (count($mid)) {
+            foreach ($mid as $result) {
+                $this->print_user_result($result);
+            }
+        } else {
+            $this->print_empty_user_result();
+        }
+        print html_writer::end_tag('tbody');
+
+        print html_writer::start_tag('thead');
+        print html_writer::start_tag('tr');
+        print html_writer::tag('th', get_string('lowlevelusers', 'adaptivequiz').':',
+            array('colspan' => '5', 'class' => 'section'));
+        print $headings;
+        print html_writer::end_tag('thead');
+
+        print html_writer::start_tag('tbody', array('class' => 'adpq_lowlevel'));
+        if (count($low)) {
+            foreach ($low as $result) {
+                $this->print_user_result($result);
+            }
+        } else {
+            $this->print_empty_user_result();
+        }
+        print html_writer::end_tag('tbody');
+
+        print html_writer::end_tag('table');
+
+        return new answers_statistic_result(count($results), ob_get_clean());
+    }
+
+    /**
+     * Print out a user result.
+     *
+     * @param stdClass $result
+     */
+    public function print_user_result(stdClass $result): void {
+        if ($result->correct) {
+            $class = 'adpq_correct';
+        } else {
+            $class = 'adpq_incorrect';
+        }
+        $url = new moodle_url('/mod/adaptivequiz/reviewattempt.php', ['attempt' => $result->attemptid]);
+        print html_writer::start_tag('tr', ['class' => $class]);
+        print html_writer::tag('td', round($result->score->measured_ability_in_scale(), 2));
+        print html_writer::tag('td', $result->user->firstname." ".$result->user->lastname);
+        print html_writer::tag('td', (($result->correct) ? "correct" : "incorrect"));
+        print html_writer::tag('td', $result->answer);
+        print html_writer::tag('td', html_writer::link($url, get_string('reviewattempt', 'adaptivequiz')));
+        print html_writer::end_tag('tr');
+    }
+
+    /**
+     * Print out an empty user-result row.
+     *
+     * @param question_analyser $analyser
+     * @param stdClass $result
+     * @return void
+     */
+    public function print_empty_user_result () {
+        print html_writer::start_tag('tr');
+        print html_writer::tag('td', '');
+        print html_writer::tag('td', '');
+        print html_writer::tag('td', '');
+        print html_writer::tag('td', '');
+        print html_writer::tag('td', '');
+        print html_writer::end_tag('tr');
+    }
+}

classes/local/questionanalysis/statistics/answers_statistic_result.php

+<?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 interface defines the methods required for pluggable statistic-results that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+class answers_statistic_result implements question_statistic_result {
+    /** @var int $count  */
+    protected $count = null;
+
+    /** @var string $printable  */
+    protected $printable = null;
+
+    /**
+     * Constructor
+     *
+     * @param int $count
+     * @return void
+     */
+    public function __construct ($count, $printable) {
+        $this->count = $count;
+        $this->printable = $printable;
+    }
+
+    /**
+     * A sortable version of the result.
+     *
+     * @return mixed string or numeric
+     */
+    public function sortable () {
+        return $this->count;
+    }
+
+    /**
+     * A printable version of the result.
+     *
+     * @param numeric $result
+     * @return mixed string or numeric
+     */
+    public function printable () {
+        return $this->printable;
+    }
+}

classes/local/questionanalysis/statistics/discrimination_statistic.php

+<?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 interface defines the methods required for pluggable statistics that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+use mod_adaptivequiz\local\questionanalysis\question_analyser;
+
+class discrimination_statistic implements question_statistic {
+    /**
+     * Answer a display-name for this statistic.
+     *
+     * @return string
+     */
+    public function get_display_name () {
+        return get_string('discrimination_display_name', 'adaptivequiz');
+    }
+
+    /**
+     * Calculate this statistic for a question's results
+     *
+     * @param question_analyser $analyser
+     * @return question_statistic_result
+     */
+    public function calculate (question_analyser $analyser) {
+        // Discrimination is generally defined as comparing the results of two sub-groups,
+        // the top 27% of test-takers (the upper group) and the bottom 27% of test-takers (the lower group),
+        // assuming a normal distribution of scores).
+        //
+        // Given that likely have a very sparse data-set we will instead categorize our
+        // responses into the upper group if the respondent's overall ability measure minus the measure's standard error
+        // is greater than the question's level. Likewise, responses will be categorized into the lower group if the respondent's
+        // ability measure plus the measure's standard error is less than the question's level.
+        // Responses where the user's ability measure and error-range include the question level will be ignored.
+
+        $level = $analyser->get_question_level_in_logits();
+        $uppergroupsize = 0;
+        $uppergroupcorrect = 0;
+        $lowergroupsize = 0;
+        $lowergroupcorrect = 0;
+
+        foreach ($analyser->get_results() as $result) {
+            if ($result->score->measured_ability_in_logits() - $result->score->standard_error_in_logits() > $level) {
+                // Upper group.
+                $uppergroupsize++;
+                if ($result->correct) {
+                    $uppergroupcorrect++;
+                }
+            } else if ($result->score->measured_ability_in_logits() + $result->score->standard_error_in_logits() < $level) {
+                // Lower Group.
+                $lowergroupsize++;
+                if ($result->correct) {
+                    $lowergroupcorrect++;
+                }
+            }
+        }
+
+        if ($uppergroupsize > 0 && $lowergroupsize > 0) {
+            // We need at least one result in the upper and lower groups.
+            $upperproportion = $uppergroupcorrect / $uppergroupsize;
+            $lowerproportion = $lowergroupcorrect / $lowergroupsize;
+            $discrimination = $upperproportion - $lowerproportion;
+            return new discrimination_statistic_result($discrimination);
+        } else {
+            // If we don't have any responses in the upper or lower group, then we don't have a meaningful result.
+            return new discrimination_statistic_result(null);
+        }
+    }
+}

classes/local/questionanalysis/statistics/discrimination_statistic_result.php

+<?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 interface defines the methods required for pluggable statistic-results that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+class discrimination_statistic_result implements question_statistic_result {
+    /** @var float $discrimination  */
+    protected $discrimination = null;
+
+    /**
+     * Constructor
+     *
+     * @param float $discrimination
+     * @return void
+     */
+    public function __construct ($discrimination) {
+        $this->discrimination = $discrimination;
+    }
+
+    /**
+     * A sortable version of the result.
+     *
+     * @return mixed string or numeric
+     */
+    public function sortable () {
+        if (is_null($this->discrimination)) {
+            return -2;
+        } else {
+            return $this->discrimination;
+        }
+    }
+
+    /**
+     * A printable version of the result.
+     *
+     * @param numeric $result
+     * @return mixed string or numeric
+     */
+    public function printable () {
+        if (is_null($this->discrimination)) {
+            return 'n/a';
+        } else {
+            return round($this->discrimination, 3);
+        }
+    }
+}

classes/local/questionanalysis/statistics/percent_correct_statistic.php

+<?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 interface defines the methods required for pluggable statistics that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+use mod_adaptivequiz\local\questionanalysis\question_analyser;
+
+class percent_correct_statistic implements question_statistic {
+    /**
+     * Answer a display-name for this statistic.
+     *
+     * @return string
+     */
+    public function get_display_name () {
+        return get_string('percent_correct_display_name', 'adaptivequiz');
+    }
+
+    /**
+     * Calculate this statistic for a question's results
+     *
+     * @param question_analyser $analyser
+     * @return question_statistic_result
+     */
+    public function calculate (question_analyser $analyser) {
+        $correct = 0;
+        $total = 0;
+        foreach ($analyser->get_results() as $result) {
+            $total++;
+            if ($result->correct) {
+                $correct++;
+            }
+        }
+        if ($total) {
+            return new percent_correct_statistic_result ($correct / $total);
+        } else {
+            return new percent_correct_statistic_result (0);
+        }
+    }
+}

classes/local/questionanalysis/statistics/percent_correct_statistic_result.php

+<?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 interface defines the methods required for pluggable statistic-results that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+class percent_correct_statistic_result implements question_statistic_result {
+    /** @var float $fraction  */
+    protected $fraction = null;
+
+    /**
+     * Constructor
+     *
+     * @param float $fraction
+     * @return void
+     */
+    public function __construct ($fraction) {
+        $this->fraction = $fraction;
+    }
+
+    /**
+     * A sortable version of the result.
+     *
+     * @return mixed string or numeric
+     */
+    public function sortable () {
+        return $this->fraction;
+    }
+
+    /**
+     * A printable version of the result.
+     *
+     * @param numeric $result
+     * @return mixed string or numeric
+     */
+    public function printable () {
+        return round($this->fraction * 100).'%';
+    }
+}

classes/local/questionanalysis/statistics/question_statistic.php

+<?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 interface defines the methods required for pluggable statistics that may be added to the question analysis.
+ *
+ * @copyright  2013 Middlebury College {@link http://www.middlebury.edu/}
+ * @copyright  2022 onwards Vitaly Potenko <potenkov@gmail.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace mod_adaptivequiz\local\questionanalysis\statistics;
+
+use mod_adaptivequiz\local\questionanalysis\question_analyser;
+
+interface question_statistic {
+    /**
+     * Answer a display-name for this statistic.
+     *
+     * @return string
+     */
+    public function get_display_name ();
+
+    /**
+     * Calculate this statistic for a question's results
+     *
+     * @param question_analyser $analyser
+     * @return question_statistic_result
+     */
+    public function calculate (question_analyser $analyser);
+}