<?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/>.
/**
 * Webservice related to courses
 * @package    local_treestudyplan
 * @copyright  2023 P.M. Kuipers
 * @license    https://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

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

require_once($CFG->libdir.'/externallib.php');

use local_treestudyplan\courseinfo;
use local_treestudyplan\associationservice;
use local_treestudyplan\local\helpers\webservicehelper;
use local_treestudyplan\completionscanner;
use local_treestudyplan\gradingscanner;
use local_treestudyplan\debug;
use core_course_category;
use moodle_exception;

/**
 * Webservice related to courses
 */
class courseservice extends \external_api {
    /**
     * Capability required to edit study plans
     * @var string
     */
    const CAP_EDIT = "local/treestudyplan:editstudyplan";
    /**
     * Capability required to view studyplans (for other users)
     * @var string
     */
    const CAP_VIEW = "local/treestudyplan:viewuserreports";

    /**
     * Get the topmost categories for the specicied user.
     * Most of the work is offloaded to an SQL query in the interest of speed,
     * but moodle functions are used to double check access permissions.
     * @param int $userid Id of the user
     * @param string $capability Capability the user must posess in the category to include it in the list.
     * @return array of core_course_category
     */
    public static function user_tops($userid=null, $capability='moodle/category:viewcourselist') {
        global $DB, $USER;
        if ($userid == null) {
            $userid = $USER->id;
        }
        $tops = [];

        if (has_capability($capability, \context_system::instance(), $userid)) {
            if ($capability == 'moodle/category:viewcourselist') {
                // We are now just looking for the visible main level categories.
                // Add all categories of depth = 1.
                $rs = $DB->get_recordset("course_categories", ["depth" => 1], 'sortorder');
                foreach ($rs as $rcat) {
                    // Get the category, and double check if the category is visible to the current user.
                    // Just in case it is a hidden category and the user does not have the viewhidden permission.
                    $cat = \core_course_category::get($rcat->id, \IGNORE_MISSING, false, $userid);
                    if ($cat !== null) {
                        // Register the category.
                        array_push($tops, $cat);
                    }
                }
                $rs->close();

            } else {
                // Context is system, but system may not be visible.
                // Return the top visible categories for this user.
                // Recurses only once.
                return self::user_tops($userid);
            }
        } else {
            // We need to search for the permissions on an individial context level.
            // This part finds all top categories with a certain permission that are also visible for the user.

            $sql = "SELECT UNIQUE ctx.* FROM {context} ctx
                    INNER JOIN {role_assignments} ra ON ra.contextid = ctx.id
                    INNER JOIN {role_capabilities} rc ON ra.roleid = rc.roleid
                    LEFT JOIN {course_categories} cat ON ctx.instanceid = cat.id
                    WHERE ( ctx.contextlevel = :ctxl_coursecat )
                    AND ra.userid = :userid AND rc.capability = :capability
                    ORDER BY ctx.depth ASC, cat.sortorder ASC";

            // Use recordset to handle the eventuality of a really big and complex moodle setup.
            $recordset = $DB->get_records_sql($sql,  ["userid" => $userid, "capability" => $capability,
                                                    "ctxl_coursecat" => \CONTEXT_COURSECAT ]);
            $params = ["userid" => $userid, "capability" => $capability,
            "ctxl_coursecat" => \CONTEXT_COURSECAT ];
            $contextids = [];
            foreach ($recordset as $r) {
                // Get the paths as an array.
                $parents = explode("/", $r->path);
                // Strip the first item, since it is an empty one.
                array_shift($parents);
                // Strip the last item, since it refers to self.
                array_pop($parents);
                // Figure out if any of the remaining parent contexts are already contexts with permission.
                $intersect = array_intersect($contextids, $parents);
                if (count($intersect) == 0) {
                    // Double check permissions according to the moodle capability system.
                    $ctx = \context::instance_by_id($r->id);
                    if (has_capability($capability, $ctx, $userid)) {
                        // Get the category, and double check if the category is visible to the current user.
                        // Just in case it is a hidden category and the user does not have the viewhidden permission.
                        $cat = \core_course_category::get($r->instanceid, \IGNORE_MISSING, false, $userid);
                        if ($cat !== null) {
                            // Register the context id in the list now, since we know the category is really visible.
                            array_push($contextids, $r->id);
                            // Register the category.
                            array_push($tops, $cat);
                        } else {
                            // The category is not visible. Add the first known visible subcategories.
                            $children = self::get_first_visible_children($r->id, $userid);
                            foreach ($children as $cat) {
                                array_push($tops, $cat);
                            }
                        }
                    }
                }
            }
        }

        return $tops;
    }

    /**
     * Find the top-most child categories for a given category that are visible.
     *
     * @param int $parentid The category to search for
     * @param int $userid The id of the user to determine visibility for
     * @return array of \core_course_category
     */
    private static function get_first_visible_children($parentid, $userid) {
        global $DB;
        $capability = 'moodle/category:viewcourselist';

        $tops = [];
        $pathlike = $DB->sql_like('ctx.path', ':pathsearch');

        $sql = "SELECT UNIQUE ctx.* FROM {context} ctx
                INNER JOIN {role_assignments} ra ON ra.contextid = ctx.id
                INNER JOIN {role_capabilities} rc ON ra.roleid = rc.roleid
                LEFT JOIN {course_categories} cat ON ctx.instanceid = cat.id
                WHERE ( ctx.contextlevel = :ctxl_coursecat )
                AND ra.userid = :userid AND rc.capability = :capability
                AND {$pathlike}
                ORDER BY ctx.depth ASC, cat.sortorder ASC";

        // Use recordset to handle the eventuality of a really big and complex moodle setup.
        $recordset = $DB->get_recordset_sql($sql,  ["userid" => $userid,
                                                    "capability" => $capability,
                                                    "ctxl_coursecat" => \CONTEXT_COURSECAT,
                                                    "pathsearch" => "%/{$parentid}/%",
                                                   ]);

        $contextids = [];
        foreach ($recordset as $r) {
            // Get the paths as an array.
            $parents = explode("/", $r->path);
            // Strip the first item, since it is an empty one.
            array_shift($parents);
            // Strip the last item, since it refers to self.
            array_pop($parents);
            // Figure out if any of the remaining parent contexts are already contexts with permission.
            $intersect = array_intersect($contextids, $parents);
            if (count($intersect) == 0) {
                // Double check permissions according to the moodle capability system.
                $ctx = \context::instance_by_id($r->id);
                if (has_capability($capability, $ctx, $userid)) {
                    // Get the category, and double check if the category is visible to the current user.
                    // Just in case it is a hidden category and the user does not have the viewhidden permission.
                    $cat = \core_course_category::get($r->instanceid, \IGNORE_MISSING, false, $userid);
                    if ($cat !== null) {
                        // Register the context id in the list now, since we know the category is really visible.
                        array_push($contextids, $r->id);
                        // Register the category.
                        array_push($tops, $cat);
                    }
                }
            }
        }
        $recordset->close();
        return $tops;
    }

    /**
     * Return value description for map_categories function
     */
    public static function map_categories_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "studyplan_id" => new \external_value(PARAM_INT, 'ID of studyplan to map the categories for', VALUE_DEFAULT),
         ] );
    }

    /**
     * Parameter description for map_categories function
     */
    public static function map_categories_returns(): \external_description {
        return new \external_multiple_structure(static::map_category_structure(false));
    }

    /**
     * Structure description for category map, used in a number of return descriptions
     * @param bool $lazy
     * @param int $value
     */
    protected static function map_category_structure($lazy = false, $value = VALUE_REQUIRED) {
        $s = [
            "id" => new \external_value(PARAM_INT, 'course category id'),
            "context_id" => new \external_value(PARAM_INT, 'course category context id'),
            "category" => contextinfo::structure(VALUE_OPTIONAL),
            "haschildren" => new \external_value(PARAM_BOOL, 'true if the category has child categories'),
            "hascourses" => new \external_value(PARAM_BOOL, 'true if the category contains courses'),
            "studyplancount" => new \external_value(PARAM_INT, 'number of linked studyplans', VALUE_OPTIONAL),
        ];

        if (!$lazy > 0) {
            $s["courses"] = new \external_multiple_structure( courseinfo::editor_structure() );
            $s["children"] = new \external_multiple_structure( static::map_category_structure(true));
        }
        return  new \external_single_structure($s, "CourseCat info", $value);
    }

    /**
     * Get a category map, and optionally specify a root category to search for
     * User's top category will be used if none specified
     * @param int $studyplanid Optional id of the studyplan to whose context to limit the search to (if so configures)
     * @return array
     */
    public static function map_categories($studyplanid = 0) {
        global $USER;

        // Determine top categories from provided context.

        if ($studyplanid == 0) {
            // On the system level, determine the user's topmost allowed catecories.
            // This uses a custom function, since moodle's "core_course_category::user_top()" is somewhat deficient.
            $children = self::user_tops();
            if (count($children) == 0) {
                throw new moodle_exception("error:nocategoriesvisible", "local_treestudyplan");
            }
        } else {
            if (\get_config("local_treestudyplan", "limitcourselist")) {
                $studyplan = studyplan::find_by_id($studyplanid);
                $context = $studyplan->context();
                if ($context->contextlevel == \CONTEXT_SYSTEM) {
                    $children = self::user_tops();
                } else if ($context->contextlevel == \CONTEXT_COURSECAT) {
                    $cat = \core_course_category::get($context->instanceid, \MUST_EXIST, true);
                    if ($cat->is_uservisible()) {
                        $children = [$cat];
                    } else {
                        $ci = new contextinfo($context);
                        $contextname = $ci->pathstr();
                        throw new moodle_exception("error:cannotviewcategory", "local_treestudyplan", '', $contextname);
                    }
                } else {
                    $children = [];
                }
            } else {
                $children = self::user_tops();
                if (count($children) == 0) {
                    throw new moodle_exception("error:nocategoriesvisible", "local_treestudyplan");
                }
            }
        }

        $list = [];
        foreach ($children as $cat) {
            $list[] = static::map_category($cat, false);
        }
        return $list;
    }

    /**
     * Return value description for get_category function
     */
    public static function get_category_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "id" => new \external_value(PARAM_INT, 'id of category'),
        ] );
    }

    /**
     * Parameter description for get_category function
     */
    public static function get_category_returns(): \external_description {
        return static::map_category_structure(false);
    }

    /**
     * Get category info by id
     * @param mixed $id
     * @return array
     */
    public static function get_category($id) {
        $cat = \core_course_category::get($id);
        return static::map_category($cat);
    }

    /**
     * Create a category map, given a specific category
     * @param core_course_category $cat The category to scan
     * @param bool $lazy If lazy loading, do not scan child categories
     * @return array
     */
    protected static function map_category(core_course_category $cat, $lazy = false) {
        global $DB;
        $catcontext = $cat->get_context();
        $ctxinfo = new contextinfo($catcontext);
        $children = $cat->get_children(); // Only shows children visible to the current user.
        $courses = $cat->get_courses();
        $model = [
            "id" => $cat->id,
            "context_id" => $catcontext->id,
            "category" => $ctxinfo->model(),
            "haschildren" => !empty($children),
            "hascourses" => !empty($courses),
        ];

        if (!$lazy) {
            $model["courses"] = [];
            foreach ($courses as $course) {
                $courseinfo = new courseinfo($course->id);
                $model["courses"][] = $courseinfo->editor_model();
            }

            $model["children"] = [];
            foreach ($children as $child) {
                $model["children"][] = static::map_category($child, true);
            }
        }

        return $model;
    }

    /**
     * List all user visible categories the current user has a given capability for.
     * @param mixed $capability
     * @return array
     */
    public static function categories_by_capability($capability) {
        global $USER;
        // List the categories in which the user has a specific capability.
        $list = [];
        $parents = self::user_tops($USER->id, $capability);
        array_merge($list, $parents);

        foreach ($parents as $parent) {
            // For optimization purposes, we include all its children now, since they will have inherited the permission.
            // #PREMATURE_OPTIMIZATION  ???.
            $list = array_merge($list, self::recursive_child_categories($parent));
        }

        return $list;
    }

    /**
     * Recursively create a list of all categories unter a specified parent
     * @param core_course_category $parent
     * @return core_course_category[]
     */
    protected static function recursive_child_categories(core_course_category $parent) {
        $list = [];
        $children = $parent->get_children();
        foreach ($children as $child) {
            $list[] = $child;
            if ($child->get_children_count() > 0) {
                $list = array_merge($list, self::recursive_child_categories($child));
            }
        }
        return $list;
    }

    /**
     * Return value description for list_available_categories function
     */
    public static function list_available_categories_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "operation" => new \external_value(PARAM_TEXT, 'type of operation ["view"|"edit"]', VALUE_DEFAULT),
            "refcontext_id" => new \external_value(PARAM_INT, 'id of reference context', VALUE_DEFAULT),
        ]);
    }

    /**
     * Parameter description for list_available_categories function
     */
    public static function list_available_categories_returns(): \external_description {
        return new \external_multiple_structure(static::map_category_structure(true));
    }

    /**
     * List all categories available to the current user for editing or viewing studyplans
     * @param string $operation The operation to scan usage for [edit, view]
     * @param int $refctxid Reference context id
     * @return array
     */
    public static function list_available_categories($operation = 'edit', $refctxid = 0) {
        global $DB;
        if ($operation == "edit") {
            $capability = self::CAP_EDIT;
        } else { // Operation == "view" || default.
            $capability = self::CAP_VIEW;
        }

        // Get the context ids of all categories the user has access to view and wich have the given permission.
        $contextids = [];
        $tops = self::user_tops(null, $capability);
        foreach ($tops as $cat) {
            $ctx = \context_coursecat::instance($cat->id);
            $contextids[] = $ctx->id;
        }

        // Now get an overview of the number of study plans in a given context.
        $contextcounts = [];
        $insertctxs = [];
        $rs = $DB->get_recordset_sql("SELECT DISTINCT context_id, COUNT(*) as num FROM {local_treestudyplan}
                                         GROUP BY context_id");
        foreach ($rs as $r) {
            // Build the counts.
            $contextcounts[$r->context_id] = $r->num;
            // Add any of the categories containing studyplans to the list.
            $ctx = \context::instance_by_id($r->context_id);
            if (has_capability($capability, $ctx) && !in_array($r->context_id, $contextids)) {
                $insertctxs[] = $ctx;
            }
        }

        $rs->close();

        $cats = [];

        // If the reference context id is not in the list, push it there if the user has proper permissions in that context.
        if ($refctxid > 1 && !in_array($refctxid, $contextids)) {
            try {
                // Get the context.
                $refctx = \context::instance_by_id($refctxid);
                // Double check permissions.
                if (has_capability($capability, $refctx)) {
                    $insertctxs[] = $refctx;
                }
            } catch (\dml_missing_record_exception $x) {
                 $refctx = null;
            }
        }

        foreach ($insertctxs as $ictx) {
            // Place this context and all relevant direct parents in the correct spots.
            $ipath = $ictx->get_parent_context_ids(true);
            $found = false;
            foreach ($ipath as $i => $pid) {
                $idx = array_search($pid, $contextids);
                if ($idx !== false) {

                    $contextids = array_merge(
                        array_slice($contextids, 0, $idx + 1),
                        array_reverse(array_slice($ipath, 0, $i)),
                        array_slice($contextids, $idx + 1, count($contextids) - 1)
                        );

                    $found = true;
                    break;
                }
            }
            if (!$found) {
                array_unshift($contextids, $ictx->id);
            }
        }

        // Now translate this to the list of categories.
        foreach ($contextids as $ctxid) {
            try {
                $ctx = \context::instance_by_id($ctxid);
                if ($ctx->contextlevel == CONTEXT_SYSTEM) {
                    $cat = \core_course_category::top();
                } else if ($ctx->contextlevel == CONTEXT_COURSECAT) {
                    $cat = \core_course_category::get($ctx->instanceid, \MUST_EXIST, false);
                }
                $cats[] = $cat;
                // In edit mode, also include direct children of the currently selected context.
                if ($operation == "edit" && $ctxid == $refctxid) {
                    // Include direct children for navigation purposes.
                    foreach ($cat->get_children() as $ccat) {
                        $ccatctx = \context_coursecat::instance($ccat->id);
                        if (!in_array($ccatctx->id, $contextids)) {
                            $cats[] = $ccat;
                        }
                    }
                }
            } catch (\dml_missing_record_exception $x) {
                 $ctx = null;
            }
        }

        // And finally build the proper models, including studyplan count in the category context.
        $list = [];
        foreach ($cats as $cat) {
            $count = 0;
            $ctxid = $cat->get_context()->id;
            if (array_key_exists($ctxid, $contextcounts)) {
                $count = $contextcounts[$ctxid];
            }

            $o = static::map_category($cat, true);
            $o["studyplancount"] = $count;
            $list[] = $o;
        }
        return $list;

    }

    /**************************************
     *
     * Progress scanners for teacherview
     *
     **************************************/

    /**
     * Return value description for scan_grade_progress function
     * @return external_function_parameters
     */
    public static function scan_grade_progress_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "gradeitemid" => new \external_value(PARAM_INT, 'Grade item ID to scan progress for', VALUE_DEFAULT),
            "studyplanid" => new \external_value(PARAM_INT, 'Study plan id to check progress in', VALUE_DEFAULT),
        ]);
    }

    /**
     * Parameter description for scan_grade_progress function
     */
    public static function scan_grade_progress_returns(): \external_description {
        return gradingscanner::structure(VALUE_REQUIRED);
    }

    /**
     * Scan grade item for progress statistics
     * @param mixed $gradeitemid Grade item id
     * @param mixed $studyplanid Id of studyitem the grade is selected in
     * @return array
     */
    public static function scan_grade_progress($gradeitemid, $studyplanid) {
        global $DB;
        // Verify access to the study plan.
        $o = studyplan::find_by_id($studyplanid);
        webservicehelper::require_capabilities(self::CAP_VIEW, $o->context());

        // Retrieve grade item.
        $gi = \grade_item::fetch(["id" => $gradeitemid]);

        // Validate course is linked to studyplan.
        $courseid = $gi->courseid;
        if (!$o->course_linked($courseid)) {
            throw new \webservice_access_exception(
                    "Course {$courseid} linked to grade item {$gradeitemid} is not linked to studyplan {$o->id()}"
                );
        }

        $scanner = new gradingscanner($gi);
        return $scanner->model();
    }

    /**
     * Return value description for scan_completion_progress function
     */
    public static function scan_completion_progress_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "criteriaid" => new \external_value(PARAM_INT, 'CriteriaID to scan progress for', VALUE_DEFAULT),
            "studyplanid" => new \external_value(PARAM_INT, 'Study plan id to check progress in', VALUE_DEFAULT),
            "courseid" => new \external_value(PARAM_INT, 'Course id of criteria', VALUE_DEFAULT),
        ]);
    }

    /**
     * Parameter description for scan_completion_progress function
     */
    public static function scan_completion_progress_returns(): \external_description {
        return completionscanner::structure(VALUE_REQUIRED);
    }

    /**
     * Scan criterium for progress statistics
     * @param mixed $criteriaid Id of criterium
     * @param mixed $studyitemid Id of studyplan relevant to this criteria
     * @return array
     */
    public static function scan_completion_progress($criteriaid, $studyitemid) {
        global $DB;
        // Verify access to the study plan.
        $item = studyitem::find_by_id($studyitemid);
        $o = $item->studyline()->studyplan();
        webservicehelper::require_capabilities(self::CAP_VIEW, $o->context());

        $crit = \completion_criteria::fetch(["id" => $criteriaid]);
        $scanner = new completionscanner($crit, $studyitemid);
        return $scanner->model();
    }

    /**
     * Return value description for scan_badge_progress function
     */
    public static function scan_badge_progress_parameters(): \external_function_parameters {
        return new \external_function_parameters( [
            "badgeid" => new \external_value(PARAM_INT, 'Badge to scan progress for', VALUE_DEFAULT),
            "studyplanid" => new \external_value(PARAM_INT,
                                'Study plan id to limit progress search to (to determine which students to scan)', VALUE_DEFAULT),
        ]);
    }

    /**
     * Parameter description for scan_badge_progress function
     */
    public static function scan_badge_progress_returns(): \external_description {
        return new \external_single_structure([
            "total" => new \external_value(PARAM_INT, 'Total number of students scanned'),
            "issued" => new \external_value(PARAM_INT, 'Number of issued badges'),
        ]);
    }

    /**
     * Scan badge for completion progress statistica
     * @param mixed $badgeid ID of the badge
     * @param mixed $studyplanid ID of the relevant study plan
     * @return array
     */
    public static function scan_badge_progress($badgeid, $studyplanid) {
        global $DB;
        // Check access to the study plan.
        $o = studyplan::find_by_id($studyplanid);
        webservicehelper::require_capabilities(self::CAP_VIEW, $o->context());

        // Validate that badge is linked to studyplan.
        if (!$o->badge_linked($badgeid)) {
            throw new \webservice_access_exception("Badge {$badgeid} is not linked to studyplan {$o->id()}");
        }

        // Get badge info.
        $badge = new \core_badges\badge($badgeid);
        $badgeinfo = new badgeinfo($badge);

        // Get the connected users.
        $students = associationservice::all_associated($studyplanid);
        // Just get the user ids.
        $studentids = array_map(function ($a) {
            return $a["id"];
        }, $students);

        return [
            "total" => count($studentids),
            "issued" => $badgeinfo->count_issued($studentids),
        ];
    }
}