<?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 qbank_statistics;

defined('MOODLE_INTERNAL') || die();
require_once($CFG->dirroot . '/mod/quiz/report/statistics/statisticslib.php');
require_once($CFG->dirroot . '/mod/quiz/report/default.php');
require_once($CFG->dirroot . '/mod/quiz/report/statistics/report.php');
require_once($CFG->dirroot . '/mod/quiz/report/reportlib.php');
require_once($CFG->dirroot . '/mod/quiz/attemptlib.php');
use core_question\statistics\questions\all_calculated_for_qubaid_condition;
use quiz_statistics_report;
/**
 * Helper for statistics
 *
 * @package    qbank_statistics
 * @copyright  2021 Catalyst IT Australia Pty Ltd
 * @author     Nathan Nguyen <nathannguyen@catalyst-au.net>
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class helper {

    /**
     * @var float Threshold to determine 'need for revision'
     */
    private const NEED_FOR_REVISION_LOWER_THRESHOLD = 30;

    /**
     * @var float Threshold to determine 'need for revision'
     */
    private const NEED_FOR_REVISION_UPPER_THRESHOLD = 50;

    /**
     * Return ids of all quizzes that use the question
     *
     * @param int $questionid id of the question
     * @return array list of quizids
     * @throws \dml_exception
     */
    public static function get_quizzes(int $questionid): array {
        global $DB;

        $quizzes = $DB->get_fieldset_sql("
             SELECT DISTINCT qa.quiz as id
                        FROM {quiz_attempts} qa
                        JOIN {question_usages} qu ON qu.id = qa.uniqueid
                        JOIN {question_attempts} qatt ON qatt.questionusageid = qu.id
                       WHERE qatt.questionid = :questionid", ['questionid' => $questionid]);
        return $quizzes;
    }

    /**
     * Load question stats from a quiz
     *
     * @param int $quizid quiz object or its id
     * @return all_calculated_for_qubaid_condition
     */
    private static function load_question_stats(int $quizid): all_calculated_for_qubaid_condition {
        // Turn to quiz object.
        $quiz = new \stdClass();
        $quiz->id = $quizid;
        // All questions, no groups.
        $report = new quiz_statistics_report();
        $questions = $report->load_and_initialise_questions_for_calculations($quiz);
        $qubaids = quiz_statistics_qubaids_condition($quiz->id, new \core\dml\sql_join());
        $progress = new \core\progress\none();
        $qcalc = new \core_question\statistics\questions\calculator($questions, $progress);
        $quizcalc = new \quiz_statistics\calculator($progress);
        if ($quizcalc->get_last_calculated_time($qubaids) === false) {
            $questionstats = $qcalc->calculate($qubaids);
        } else {
            $questionstats = $qcalc->get_cached($qubaids);
        }
        return $questionstats;
    }

    /**
     * Load a specified stats item for a question
     *
     * @param int $quizid quiz id
     * @param int $questionid question id
     * @param string $item a stats item
     * @return float|int
     */
    public static function load_question_stats_item(int $quizid, int $questionid, string $item): ?float {
        $questionstats = self::load_question_stats($quizid);
        // Find in main question.
        foreach ($questionstats->questionstats as $stats) {
            if ($stats->questionid == $questionid && isset($stats->$item)) {
                return $stats->$item;
            }
        }
        // If not found, find in sub questions.
        foreach ($questionstats->subquestionstats as $stats) {
            if ($stats->questionid == $questionid && isset($stats->$item)) {
                return $stats->$item;
            }
        }
        return null;
    }

    /**
     * Calculate average for a stats item on a question.
     *
     * @param int $questionid id of the question
     * @param string $item stats item
     * @return float|null
     */
    private static function calculate_average_question_stats_item(int $questionid, string $item): ?float {
        $quizzes = self::get_quizzes($questionid);

        $sum = 0;
        $quizcount = count($quizzes);
        foreach ($quizzes as $quizid) {
            $value = self::load_question_stats_item($quizid, $questionid, $item);
            if (!is_null($value)) {
                $sum += $value;
            } else {
                // Exclude this value when it is null.
                $quizcount--;
            }
        }

        // Return null if there is no quizzes.
        if (empty($quizcount)) {
            return null;
        }

        // Average value per quiz.
        $average = $sum / $quizcount;
        return $average;
    }

    /**
     * Calculate average facility index
     *
     * @param int $questionid
     * @return float|null
     */
    public static function calculate_average_question_facility(int $questionid): ?float {
        return self::calculate_average_question_stats_item($questionid, 'facility');
    }

    /**
     * Calculate average discriminative efficiency
     *
     * @param int $questionid question id
     * @return float|null
     */
    public static function calculate_average_question_discriminative_efficiency(int $questionid): ?float {
        return self::calculate_average_question_stats_item($questionid, 'discriminativeefficiency');
    }

    /**
     * Calculate average discriminative efficiency
     *
     * @param int $questionid question id
     * @return float|null
     */
    public static function calculate_average_question_discrimination_index(int $questionid): ?float {
        return self::calculate_average_question_stats_item($questionid, 'discriminationindex');
    }

    /**
     * Format a number to a localised percentage with specified decimal points.
     *
     * @param float|null $number The number being formatted
     * @param bool $fraction An indicator for whether the number is a fraction or is already multiplied by 100
     * @param int $decimals Sets the number of decimal points
     * @return string
     * @throws \coding_exception
     */
    public static function format_percentage(?float $number, bool $fraction = true, int $decimals = 2): string {
        if (is_null($number)) {
            return get_string('na', 'qbank_statistics');
        }
        $coefficient = $fraction ? 100 : 1;
        return get_string('percents', 'moodle', format_float($number * $coefficient, $decimals));
    }

    /**
     * Format discrimination index (need for revision).
     *
     * @param float|null $value stats value
     * @return array
     */
    public static function format_discrimination_index(?float $value): array {
        if (is_null($value) || $value < self::NEED_FOR_REVISION_LOWER_THRESHOLD) {
            $content = get_string('verylikely', 'qbank_statistics');
            $classes = 'alert-danger';
        } else if ($value < self::NEED_FOR_REVISION_UPPER_THRESHOLD) {
            $content = get_string('likely', 'qbank_statistics');
            $classes = 'alert-warning';
        } else {
            $content = get_string('unlikely', 'qbank_statistics');
            $classes = 'alert-success';
        }
        return [$content, $classes];
    }
}