<?php
// This file is part of the Studyplan plugin for Moodle
//
// 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 <https://www.gnu.org/licenses/>.
/**
 *
 * @package    local_treestudyplan
 * @copyright  2023 P.M. Kuipers
 * @license    https://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

namespace local_treestudyplan;

class teachingfinder {
    const TABLE = "local_treestudyplan_teachers";

    public static function list_my_plans() {
        global $USER, $DB;
        $userid = $USER->id;

        $records = $DB->get_records(self::TABLE, ['teacher_id' => $userid]);
        if (count($records) == 0) {
            // Initiate a search if the cache is empty.
            self::update_teaching_cache($userid);
             $DB->get_records(self::TABLE, ['teacher_id' => $userid]);
        }
        $list = [];
        foreach ($records as $r) {
            $list[] = studyplan::findById($r->studyplan_id);
        }
        return $list;
    }

    /**
     * Find The active studyplans where the specified user is a teacher
     * (Has the  mod/assign::grade capability in one of the linked courses)
     * TODO: OPTIMIZE THIS CHECK!!!
     */
    public static function update_teaching_cache($userid) {
        global $DB;
        $list = [];

        // First find all active study plans.

        $sql = "SELECT p.id FROM {local_treestudyplan_page} p
            WHERE startdate <= NOW() and enddate >= NOW()";
        $pageids = $DB->get_fieldset_sql($sql, []);

        // Then parse them to see if the user has the grading permission in any of them .
        // (Which would make them a teacher for all intents and purposes).

        foreach ($pageids as $pageid) {
            $sql = "SELECT i.course_id FROM {local_treestudyplan_item} i
                    INNER JOIN {local_treestudyplan_line} l ON i.line_id = l.id
                    WHERE l.page_id = :page_id AND i.course_id IS NOT NULL";
            $courseids = $DB->get_fieldset_sql($sql, ["page_id" => $pageid]);

            $linked = false;
            foreach ($courseids as $cid) {
                $coursecontext = \context_course::instance($cid);
                if (is_enrolled($coursecontext, $userid, 'mod/assign:grade')) {
                    $linked = true;
                    break; // No need to search further.
                }
            }

            if ($linked) {
                $list[] = $pageid;
            }

        }

        // Now, clear the database of all records for this user.
        $DB->delete_records(self::TABLE, ["teacher_id" => $userid]);
        // And add new records for the found studyplans.
        $now = time();
        foreach ($list as $pageid) {
            // Retrieve the studyplan id from the page.
            // TODO: Change this when page management is implemented to return the page instead of the plan.
            $planid = $DB->get_field("local_treestudyplan_page", "studyplan_id", ["id" => $pageid]);
            $DB->insert_record(self::TABLE, ["teacher_id" => $userid, "studyplan_id" => $planid, "update_time" => $now]);
        }

        return $list;
    }

    public static function list_teacher_ids() {
        global $DB;
        return $DB->get_fieldset_sql("SELECT DISTINCT teacher_id FROM {".self::TABLE."}");
    }

    public static function get_update_time($teacherid): int {
        global $DB;
        $r = $DB->get_field_sql("SELECT MIN(update_time)FROM {".self::TABLE."} WHERE teacher_id=:teacher_id",
                                ["teacher_id" => $teacherid]);
        return (int)($r->update_time);
    }

}