<?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/>.
/**
 * Studyplan page management class
 * @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($CFG->libdir.'/externallib.php');
require_once($CFG->libdir.'/filelib.php');
/**
 * Studyplan page management class
 */
class studyplanpage {

    /**
     * Database table this class models for
     * @var string */
    const TABLE = "local_treestudyplan_page";
    /**
     * Cache for finding previously loaded pages
     * @var array */
    private static $cache = [];

    /**
     * Holds database record
     * @var stdClass
     */
    private $r;
    /** @var int */
    private $id;
    /** @var studyplan*/
    private $studyplan;

    /**
     * Get aggregator for the studyplan (page)
     * @return aggregator
     */
    public function aggregator(): aggregator {
        return $this->studyplan->aggregator();
    }

    /**
     * Find record in database and return management object
     * @param int $id Id of database record
     */
    public static function find_by_id($id): self {
        if (!array_key_exists($id, self::$cache)) {
            self::$cache[$id] = new self($id);
        }
        return self::$cache[$id];
    }

    /**
     * Construct new instance from DB record
     * @param int $id Id of database record
     */
    private function __construct($id) {
        global $DB;
        $this->id = $id;
        $this->r = $DB->get_record(self::TABLE, ['id' => $id]);
        $this->studyplan = studyplan::find_by_id($this->r->studyplan_id);
    }

    /**
     * Return database identifier
     * @return int
     */
    public function id() {
        return $this->id;
    }

    /**
     * Find studyplan for this page
     */
    public function studyplan(): studyplan {
        return $this->studyplan;
    }

    /**
     * Return short name
     * @return string
     */
    public function shortname() {
        return $this->r->shortname;
    }

    /**
     * Numer of periods for this page
     */
    public function periods() {
        return $this->r->periods;
    }

    /**
     * Return full name
     * @return string
     */
    public function fullname() {
        return $this->r->fullname;
    }

    /**
     * Start date
     * @return \DateTime
     */
    public function startdate() {
        return new \DateTime($this->r->startdate);
    }

    /**
     * End date
     * @param bool $farahead Return a date 100 years in the future if end date is not set. Returns null otherwise
     * @return \DateTime|null
     */
    public function enddate($farahead = true) {
        if ($this->r->enddate && strlen($this->r->enddate) > 0) {
            return new \DateTime($this->r->enddate);
        } else {
            // Return a date 100 years into the future.
            if ($farahead) {
                return (new \DateTime($this->r->startdate))->add(new \DateInterval("P100Y"));
            } else {
                return null;
            }
        }

    }

    /**
     * Return description with all file references resolved
     * @return string
     */
    public function description() {
        $text = \file_rewrite_pluginfile_urls(
            // The content of the text stored in the database.
            $this->r->description,
            // The pluginfile URL which will serve the request.
            'pluginfile.php',

            // The combination of contextid / component / filearea / itemid.
            // Form the virtual bucket that file are stored in.
            \context_system::instance()->id, // System instance is always used for this.
            'local_treestudyplan',
            'studyplanpage',
            $this->id
        );
        return $text;
    }

    /**
     * Determine studyplan timing
     * @return string
     */
    public function timing() {
        $now = new \DateTime();
        if ($now > $this->startdate()) {
            if ($now > $this->enddate()) {
                return "past";
            } else {
                return "present";
            }
        } else {
            return "future";
        }
    }

    /**
     * Webservice structure for basic info
     * @param int $value Webservice requirement constant
     */
    public static function simple_structure($value = VALUE_REQUIRED): \external_description {
        return new \external_single_structure([
            "id" => new \external_value(PARAM_INT, 'id of studyplan page'),
            "fullname" => new \external_value(PARAM_TEXT, 'name of studyplan page'),
            "shortname" => new \external_value(PARAM_TEXT, 'shortname of studyplan page'),
            "periods" => new \external_value(PARAM_INT, 'number of periods in studyplan page'),
            "description" => new \external_value(PARAM_RAW, 'description of studyplan page'),
            "startdate" => new \external_value(PARAM_TEXT, 'start date of studyplan'),
            "enddate" => new \external_value(PARAM_TEXT, 'end date of studyplan'),
            "timing" => new \external_value(PARAM_TEXT, '(past|present|future)'),
            "perioddesc" => period::page_structure(),
            "timeless" => new \external_value(PARAM_BOOL, 'Page does not in'),
        ], 'Studyplan page basic info', $value);
    }

    /**
     * Webservice model for basic info
     * @return array Webservice data model
     */
    public function simple_model() {
        return [
            'id' => $this->r->id,
            'fullname' => $this->r->fullname,
            'shortname' => $this->r->shortname,
            'periods' => $this->r->periods,
            'description' => $this->description(),
            'startdate' => $this->r->startdate,
            'enddate' => $this->r->enddate,
            'timing' => $this->timing(),
            "perioddesc" => period::page_model($this),
            'timeless' => \get_config("local_treestudyplan", "timelessperiods"),
        ];
    }

    /**
     * Webservice structure for editor info
     * @param int $value Webservice requirement constant
     */
    public static function editor_structure($value = VALUE_REQUIRED): \external_description {
        return new \external_single_structure([
            "id" => new \external_value(PARAM_INT, 'id of studyplan'),
            "fullname" => new \external_value(PARAM_TEXT, 'name of studyplan page'),
            "shortname" => new \external_value(PARAM_TEXT, 'shortname of studyplan page'),
            "description" => new \external_value(PARAM_RAW, 'description of studyplan page'),
            "periods" => new \external_value(PARAM_INT, 'number of periods in studyplan page'),
            "startdate" => new \external_value(PARAM_TEXT, 'start date of studyplan page'),
            "enddate" => new \external_value(PARAM_TEXT, 'end date of studyplan page'),
            "timing" => new \external_value(PARAM_TEXT, '(past|present|future)'),
            "studylines" => new \external_multiple_structure(studyline::editor_structure()),
            "perioddesc" => period::page_structure(),
            "timeless" => new \external_value(PARAM_BOOL, 'Page does not include time information'),
            ], 'Studyplan page full structure', $value);
    }

    /**
     * Webservice model for editor info
     * @return array Webservice data model
     */
    public function editor_model() {
        global $DB;

        $model = [
            'id' => $this->r->id,
            'fullname' => $this->r->fullname,
            'shortname' => $this->r->shortname,
            'description' => $this->description(),
            'periods' => $this->r->periods,
            'startdate' => $this->r->startdate,
            'enddate' => $this->r->enddate,
            'timing' => $this->timing(),
            'studylines' => [],
            "perioddesc" => period::page_model($this),
            'timeless' => \get_config("local_treestudyplan", "timelessperiods"),
        ];

        $children = studyline::find_page_children($this);
        foreach ($children as $c) {
            $model['studylines'][] = $c->editor_model();
        }
        return $model;
    }

    /**
     * Add new study plan page
     * @param mixed $fields Parameter for new study plan page
     * @param bool $bare If true, do not create a first page with copy of studyplan names
     */
    public static function add($fields, $bare = false): self {
        global $DB;

        if (!isset($fields['studyplan_id'])) {
            throw new \InvalidArgumentException("parameter 'studyplan_id' missing");
        } else {
            $plan = studyplan::find_by_id($fields['studyplan_id']);

        }

        $addable = ['studyplan_id', 'fullname', 'shortname', 'description', 'descriptionformat', 'periods', 'startdate', 'enddate'];
        $info = ['enddate' => null ];
        foreach ($addable as $f) {
            if (array_key_exists($f, $fields)) {
                $info[$f] = $fields[$f];
            }
        }
        if (!isset($info['periods'])) {
            $info['periods'] = 4;
        } else if ($info['periods'] < 1) {
            $info['periods'] = 1;
        }

        $id = $DB->insert_record(self::TABLE, $info);
        // Refresh the page cache for the studyplan.
        $plan->pages(true);
        $page = self::find_by_id($id); // Make sure the new page is immediately cached.

        if (!$bare) {

            if (get_config("local_treestudyplan", "copystudylinesnewpage")) {
                $templatepage = null;
                $templatelines = [];
                // Find the latest a page with lines in the plan.
                $pages = $plan->pages(true);
                foreach ($pages as $p) {
                    if ($p->id() != $id) {
                        $lines = studyline::find_page_children($p);
                        if (count($lines) > 0) {
                            $templatepage = $p;
                            $templatelines = $lines;
                        }
                    }
                }

                if (isset($templatepage)) {
                    foreach ($templatelines as $l) {
                        $map = []; // Bare copy still requires passing an empty array.
                        $l->duplicate($page, $map, true); // Do bare copy, which does not include line content.
                    }
                }
            }

            if (count(studyline::find_page_children($page)) == 0) {
                // Add an empty study line if there are currently no study lines.
                $lineinfo = ['page_id' => $id,
                            'name' => get_string("default_line_name", "local_treestudyplan"),
                            'shortname' => get_string("default_line_shortname", "local_treestudyplan"),
                            "color" => "#DDDDDD",
                                ];
                studyline::add($lineinfo);
            }
        }

        return $page;
    }

    /**
     * Edit studyplan page
     * @param mixed $fields Parameters to change
     */
    public function edit($fields): self {
        global $DB;
        $editable = ['fullname', 'shortname', 'description', 'descriptionformat', 'periods', 'startdate', 'enddate'];
        $info = ['id' => $this->id ];
        foreach ($editable as $f) {
            if (array_key_exists($f, $fields)) {
                $info[$f] = $fields[$f];
            }
        }
        if (isset($info['periods']) && $info['periods'] < 1) {
            $info['periods'] = 1;
        }

        $DB->update_record(self::TABLE, $info);
        // Reload record after edit.
        $this->r = $DB->get_record(self::TABLE, ['id' => $this->id], "*", MUST_EXIST);

        return $this;
    }

    /**
     * Delete study plan page
     * @param bool $force Force deletion even if not empty
     * @return success
     */
    public function delete($force = false) {
        global $DB;

        if ($force) {
            $children = studyline::find_page_children($this);
            foreach ($children as $c) {
                $c->delete($force);
            }
        }

        if ($DB->count_records('local_treestudyplan_line', ['page_id' => $this->id]) > 0) {
            return success::fail('cannot delete studyplan page that still has studylines');
        } else {
            $DB->delete_records(self::TABLE, ['id' => $this->id]);
            return success::success();
        }
    }

    /**
     * Webservice structure for userinfo
     * @param int $value Webservice requirement constant
     */
    public static function user_structure($value = VALUE_REQUIRED): \external_description {
        return new \external_single_structure([
            "id" => new \external_value(PARAM_INT, 'id of studyplan page'),
            "fullname" => new \external_value(PARAM_TEXT, 'name of studyplan page'),
            "shortname" => new \external_value(PARAM_TEXT, 'shortname of studyplan page'),
            "description" => new \external_value(PARAM_RAW, 'description of studyplan page'),
            "periods" => new \external_value(PARAM_INT, 'number of slots in studyplan page'),
            "startdate" => new \external_value(PARAM_TEXT, 'start date of studyplan page'),
            "enddate" => new \external_value(PARAM_TEXT, 'end date of studyplan page'),
            "timing" => new \external_value(PARAM_TEXT, '(past|present|future)'),
            "studylines" => new \external_multiple_structure(studyline::user_structure()),
            "perioddesc" => period::page_structure(),
            "timeless" => new \external_value(PARAM_BOOL, 'Page does not include time information'),
        ], 'Studyplan page with user info', $value);
    }

    /**
     * Webservice model for user info
     * @param int $userid ID of user to check specific info for
     * @return array Webservice data model
     */
    public function user_model($userid) {

        $model = [
            'id' => $this->r->id,
            'fullname' => $this->r->fullname,
            'shortname' => $this->r->shortname,
            'description' => $this->description(),
            'periods' => $this->r->periods,
            'startdate' => $this->r->startdate,
            'enddate' => $this->r->enddate,
            'timing' => $this->timing(),
            'studylines' => [],
            "perioddesc" => period::page_model($this),
            'timeless' => \get_config("local_treestudyplan", "timelessperiods"),
        ];

        $children = studyline::find_page_children($this);
        foreach ($children as $c) {
            $model['studylines'][] = $c->user_model($userid);
        }
        return $model;
    }

    /**
     * Scan user progress (completed modules) over this page for a specific user
     * @param int $userid ID of user to check for
     * @return float Fraction of completion
     */
    public function scanuserprogress($userid) {
        $courses = 0;
        $completed = 0;

        foreach (studyline::find_page_children($this) as $line) {
            $items = studyitem::find_studyline_children($line);
            foreach ($items as $c) {
                if (in_array($c->type(), studyline::COURSE_TYPES)) {
                    $courses += 1;
                    if ($c->completion($userid) >= completion::COMPLETED) {
                        $completed += 1;
                    }
                }
            }
        }
        if ($courses > 0) {
            return ($completed / $courses);
        } else {
            return 0;
        }

    }

    /**
     * Find list of pages belonging to a specified study plan
     * @param studyplan $plan Studyplan to search pages for
     * @return studyplanpage[]
     */
    public static function find_studyplan_children(studyplan $plan) {
        global $DB;
        $list = [];
        $ids = $DB->get_fieldset_select(self::TABLE, "id", "studyplan_id = :plan_id ORDER BY startdate",
                                        ['plan_id' => $plan->id()]);
        foreach ($ids as $id) {
            $list[] = self::find_by_id($id);
        }
        return $list;
    }

    /**
     * Duplicate a studyplan page
     * @param int $pageid Id of the page to copy
     * @param studyplan $newstudyplan Studyplan to copy the page into
     */
    public static function duplicate_page(int $pageid, studyplan $newstudyplan): self {
        $ori = self::find_by_id($pageid);
        $new = $ori->duplicate($newstudyplan);
        return $new;
    }

    /**
     * Duplicate this studyplan page
     * @param studyplan $newstudyplan Studyplan to copy the page into
     * @param \DateInterval|null $timeoffset Amount if time to shift the dates for the new page
     */
    public function duplicate(studyplan $newstudyplan, $timeoffset = null): self {
        if ($timeoffset == null) {
            $timeoffset = new \DateInterval("P0D");
        }

        // First duplicate the studyplan structure.
        $new = self::add([
            'studyplan_id' => $newstudyplan->id(),
            'fullname' => $this->r->fullname,
            'shortname' => $this->r->shortname,
            'description' => $this->r->description,
            'pages' => $this->r->pages,
            'startdate' => $this->startdate()->add($timeoffset)->format("Y-m-d"),
            'enddate' => empty($this->r->enddate) ? null : ($this->enddate()->add($timeoffset)->format("Y-m-d")),
        ]);

        // Copy any files related to this page.
        $areas = ["studyplanpage"];
        $fs = \get_file_storage();
        foreach ($areas as $area) {
            $files = $fs->get_area_files(
                \context_system::instance()->id,
                "local_treestudyplan",
                $area,
                $this->id()
            );
            foreach ($files as $file) {
                $path = $file->get_filepath();
                $filename = $file->get_filename();
                if ($filename != ".") {
                    // Prepare new file info for the target file.
                    $fileinfo = [
                        'contextid' => \context_system::instance()->id, // System context.
                        'component' => 'local_treestudyplan',           // Your component name.
                        'filearea'  => $area,                           // Area name.
                        'itemid'    => $new->id(),                      // Study plan id.
                        'filepath'  => $path,                           // Original file path.
                        'filename'  => $filename,                       // Original file name.
                    ];
                    // Copy existing file into new file.
                    $fs->create_file_from_storedfile($fileinfo, $file);
                }
            }
        }

        // Adjust the time offsets of the periods.
        foreach ($this->periods() as $p) {
            $p->edit([
                'startdate' => $p->startdate()->add($timeoffset)->format("Y-m-d"),
                'enddate' => $p->enddate()->add($timeoffset)->format("Y-m-d"),
            ]);
        }

        // Now , copy the studylines.
        $children = studyline::find_page_children($this);
        $itemtranslation = []; // Stores ids of original and copied items.
        $linetranslation = []; // Stores ids of original and copied lines.
        foreach ($children as $c) {
            $translation = [];
            $newchild = $c->duplicate($new, $translation);
            $itemtranslation += $translation;   // Fixes behaviour where translation array is reset on each call.
            $linetranslation[$c->id()] = $newchild->id();
        }

        // Now the itemtranslation array contains all of the old child id's as keys and all of the related new ids as values.
        // (feature of the studyline::duplicate function).
        // Use this to recreate the lines in the new plan.
        foreach (array_keys($itemtranslation) as $itemid) {
            // Copy based on the outgoing connections of each item, to avoid duplicates.
            $connections  = studyitemconnection::find_outgoing($itemid);
            foreach ($connections as $conn) {
                studyitemconnection::connect($itemtranslation[$conn->from_id()], $itemtranslation[$conn->to_id()]);
            }
        }
        return $new;
    }

    /**
     * Description of export structure for webservices
     */
    public static function export_structure(): \external_description {
        return new \external_single_structure([
            "format" => new \external_value(PARAM_TEXT, 'format of studyplan export'),
            "content" => new \external_value(PARAM_RAW, 'exported studyplan content'),
        ], 'Exported studyplan');
    }

    /**
     * Export this page into a json model
     * @return array
     */
    public function export_page() {
        $model = $this->export_model();
        $json = json_encode([
            "type" => "studyplanpage",
            "version" => 2.0,
            "page" => $model,
            ], \JSON_PRETTY_PRINT);
        return [ "format" => "application/json", "content" => $json];
    }

    /**
     * Export this page into a csv model
     * @return array
     */
    public function export_page_csv() {
        $plist = period::find_for_page($this);

        $model = $this->editor_model();

        $periods = intval($model["periods"]);
        // First line.
        $csv = "\"\"";
        for ($i = 1; $i <= $periods; $i++) {
            $name = $plist[$i]->shortname();
            $csv .= ", \"{$name}\"";
        }
        $csv .= "\r\n";
        // Next, make one line per studyline.
        foreach ($model["studylines"] as $line) {
            // Determine how many fields are simultaneous in the line at maximum.
            $maxlines = 1;
            for ($i = 1; $i <= $periods; $i++) {
                if (count($line["slots"]) > $i) {
                    $ct = 0;
                    foreach ($line["slots"][$i][studyline::SLOTSET_COURSES] as $itm) {
                        if ($itm["type"] == "course") {
                            $ct += 1;
                        }
                    }
                    if ($ct > $maxlines) {
                        $maxlines = $ct;
                    }

                }
            }

            for ($lct = 0; $lct < $maxlines; $lct++) {
                $csv .= "\"{$line["name"]}\"";
                for ($i = 1; $i <= $periods; $i++) {
                    $filled = false;
                    if (count($line["slots"]) > $i) {
                        $ct = 0;
                        foreach ($line["slots"][$i][studyline::SLOTSET_COURSES] as $itm) {
                            if ($itm["type"] == "course") {
                                if ($ct == $lct) {
                                    $csv .= ", \"";
                                    $csv .= $itm["course"]["fullname"];
                                    $csv .= "\r\n";
                                    $first = true;
                                    foreach ($itm["course"]["grades"] as $g) {
                                        if ($g["selected"]) {
                                            if ($first) {
                                                $first = false;
                                            } else {
                                                $csv .= "\r\n";
                                            }
                                            $csv .= "- ".str_replace('"', '\'', $g["name"]);
                                        }
                                    }
                                    $csv .= "\"";
                                    $filled = true;
                                    break;
                                }
                                $ct++;
                            }
                        }
                    }
                    if (!$filled) {
                        $csv .= ", \"\"";
                    }
                }
                $csv .= "\r\n";
            }
        }

        return [ "format" => "text/csv", "content" => $csv];
    }

    /**
     * Export this page's studylines into a json model
     * @return array
     */
    public function export_studylines() {
        $model = $this->export_studylines_model();
        $json = json_encode([
            "type" => "studylines",
            "version" => 2.0,
            "studylines" => $model,
            ], \JSON_PRETTY_PRINT);
        return [ "format" => "application/json", "content" => $json];
    }

    /**
     * Export this pages periods into a json model
     * @return array
     */
    public function export_periods() {
        $model = period::page_model($this);
        $json = json_encode([
            "type" => "periods",
            "version" => 2.0,
            "perioddesc" => $model,
            ], \JSON_PRETTY_PRINT);
        return [ "format" => "application/json", "content" => $json];
    }

    /**
     * Export essential information for export
     * @return array information model
     */
    public function export_model() {
        $exportfiles = $this->export_files('studyplanpage');

        $model = [
            'fullname' => $this->r->fullname,
            'shortname' => $this->r->shortname,
            'description' => $this->r->description,
            'descriptionformat' => $this->r->descriptionformat,
            'periods' => $this->r->periods,
            'startdate' => $this->r->startdate,
            'enddate' => $this->r->enddate,
            'studylines' => $this->export_studylines_model(),
            'perioddesc' => period::page_model($this),
            'files' => $exportfiles,
        ];
        return $model;
    }

    /**
     * Export files from file storage
     * @param string $area Name of the file area to export
     * @return array information model
     */
    public function export_files($area) {
        $exportfiles = [];
        $fs = get_file_storage();
        $files = $fs->get_area_files(
            \context_system::instance()->id,
            'local_treestudyplan',
            $area,
            $this->id);
        foreach ($files as $file) {
            if ($file->get_filename() != ".") {
                $contents = $file->get_content();
                $exportfiles[] = [
                    "name" => $file->get_filename(),
                    "path" => $file->get_filepath(),
                    "content" => convert_uuencode($contents),
                ];
            }
        }
        return $exportfiles;
    }

    /**
     * Import previously exported files into the file storage
     * @param mixed $importfiles List of files to import from string in the format exported in export_model()
     * @param string $area Name of the file area to export
     */
    public function import_files($importfiles, $area) {
        $fs = get_file_storage();
        foreach ($importfiles as $file) {
            if ($file['name'] != ".") {
                $fileinfo = [
                    'contextid' => \context_system::instance()->id,   // ID of the system context.
                    'component' => 'local_treestudyplan', // Your component name.
                    'filearea'  => $area,                 // Usually = table name.
                    'itemid'    => $this->id,             // ID of the studyplanpage.
                    'filepath'  => $file["path"],         // Path of the file.
                    'filename'  => $file["name"],         // Name of the file..
                ];

                $fs->create_file_from_string($fileinfo, convert_uudecode($file["content"]));
            }
        }
    }

    /**
     * Export this pages periods into an array before serialization
     * @return array
     */
    public function export_studylines_model() {
        $children = studyline::find_page_children($this);
        $lines = [];
        foreach ($children as $c) {
            $lines[] = $c->export_model();
        }
        return $lines;
    }

    /**
     * Import periods from file contents
     * @param string $content String
     * @param string $format Format description
     */
    public function import_periods($content, $format = "application/json") {
        if ($format != "application/json") {
            return false;
        }
        $content = json_decode($content, true);
        if ($content["type"] == "periods" && $content["version"] >= 2.0) {
            return $this->import_periods_model($content["perioddesc"]);
        } else if ($content["type"] == "studyplanpage" && $content["version"] >= 2.0) {
            return $this->import_periods_model($content["page"]["perioddesc"]);
        } else {
            return false;
        }
    }

    /**
     * Import studylines from file contents
     * @param string $content String
     * @param string $format Format description
     */
    public function import_studylines($content, $format = "application/json") {
        if ($format != "application/json") {
            return false;
        }
        $content = json_decode($content, true);
        if ($content["type"] == "studylines" && $content["version"] >= 2.0) {
            return $this->import_studylines_model($content["studylines"]);
        } else if ($content["type"] == "studyplanpage" && $content["version"] >= 2.0) {
            return $this->import_studylines_model($content["page"]["studylines"]);
        } else if ($content["type"] == "studyplan" && $content["version"] >= 2.0) {
            return $this->import_studylines_model($content["studyplan"]["pages"][0]["studylines"]);
        } else {
            return false;
        }
    }

    /**
     * Find a studyline in this page by its shortname
     * @param string $shortname
     * @return studyline|null
     */
    protected function find_studyline_by_shortname($shortname) {
        $children = studyline::find_page_children($this);
        foreach ($children as $l) {
            if ($shortname == $l->shortname()) {
                return $l;
            }
        }
        return null;
    }

    /**
     * Import periods from decoded array model
     * @param array $model Decoded array
     */
    public function import_periods_model($model) {
        $periods = period::find_for_page($this);
        foreach ($model as $pmodel) {
            $pi = $pmodel["period"];
            if (array_key_exists($pi, $periods)) {
                $periods[$pi]->edit($pmodel);
            }
        }
    }

    /**
     * Import studylines from decoded array model
     * @param array $model Decoded array
     */
    public function import_studylines_model($model) {
        // First attempt to map each studyline model to an existing or new line.
        $linemap = [];
        foreach ($model as $ix => $linemodel) {
            $line = $this->find_studyline_by_shortname($linemodel["shortname"]);
            if (empty($line)) {
                $linemodel["page_id"] = $this->id;
                $line = studyline::add($linemodel);
            }
            $linemap[$ix] = $line;
        }

        // Next, let each study line import the study items.
        $itemtranslation = [];
        $itemconnections = [];
        foreach ($model as $ix => $linemodel) {
            $translation = [];
            $connections = [];
            $linemap[$ix]->import_studyitems($linemodel["slots"], $translation, $connections);
            $itemtranslation += $translation;  // Fixes behaviour where translation array is reset on each call.
            $itemconnections += $connections;
        }

        // Finally, create the links between the study items.
        foreach ($itemconnections as $from => $dests) {
            foreach ($dests as $to) {
                studyitemconnection::connect($from, $itemtranslation[$to]);
            }
        }
        return true;
    }

}