<?php

namespace RoosterLMS\Learn;

use RoosterLMS\Blocks\Learner;
use RoosterLMS\Blocks\Locks;
use RoosterLMS\Content\CatalogueQuery;
use RoosterLMS\Content\Item;
use RoosterLMS\Content\LinkKind;
use RoosterLMS\Content\ObjectType;
use RoosterLMS\Domain\Services;
use RoosterLMS\Enrolment\AccessReason;
use RoosterLMS\Enrolment\EnrolmentStatus;
use RoosterLMS\I18n\Switcher;
use RoosterLMS\Routing\Urls;

defined( 'ABSPATH' ) || exit;

final class LessonNav {

	public const SAID = 'rl_said';

	private const COURSES_MAX = 100;

	public static function for_item( int $user_id, Item $item, bool $completable, bool $done ): array {
		$lang   = Switcher::current();
		$listed = self::listed( $item->course_id, $lang );
		$index  = null;
		foreach ( $listed['items'] as $i => $entry ) {
			if ( $entry->id === $item->id ) {
				$index = $i;
				break;
			}
		}
		if ( null === $index ) {
			return array(
				'previous' => null,
				'next'     => null,
			);
		}
		return array(
			'previous' => self::previous( $user_id, $item, $listed, $index, $lang ),
			'next'     => self::next( $user_id, $item, $listed, $index, $lang, $completable, $done ),
		);
	}

	private static function next( int $user_id, Item $item, array $listed, int $index, string $lang, bool $completable, bool $done ): ?array {
		$gate  = Services::gate();
		$count = count( $listed['items'] );
		for ( $i = $index + 1; $i < $count; $i++ ) {
			$entry    = $listed['items'][ $i ];
			$decision = $gate->can_open_item( $user_id, $entry->id );
			if ( $decision->allowed ) {
				return self::step( $entry, $listed['posts'], $lang, true );
			}
			if ( AccessReason::LOCKED_SEQUENCE !== $decision->reason ) {
				continue;
			}
			$waits = ! $done && $gate->previous_item( $user_id, $entry ) === $item->id;
			if ( $waits && $completable ) {
				return array( 'needs' => true ) + self::step( $entry, $listed['posts'], $lang, true );
			}
			$reason = Locks::item_reason( $decision->reason, $entry, $user_id );
			return array(
				'waits'  => $waits,
				'reason' => '' !== $reason ? $reason : __( 'Not available yet.', 'rooster-lms' ),
			) + self::step( $entry, $listed['posts'], $lang, false );
		}
		$other = self::other_course( $user_id, $item->course_id, true, $lang );
		if ( null !== $other ) {
			return $other;
		}
		$page = self::course_page( $item->course_id, $lang );
		return $page['open'] ? $page : null;
	}

	private static function previous( int $user_id, Item $item, array $listed, int $index, string $lang ): ?array {
		for ( $i = $index - 1; $i >= 0; $i-- ) {
			$entry = $listed['items'][ $i ];
			if ( Services::gate()->can_open_item( $user_id, $entry->id )->allowed ) {
				return self::step( $entry, $listed['posts'], $lang, true );
			}
		}
		return self::other_course( $user_id, $item->course_id, false, $lang );
	}

	private static function other_course( int $user_id, int $course_id, bool $forward, string $lang ): ?array {
		$gate      = Services::gate();
		$takes     = array();
		$candidate = array();
		foreach ( $forward ? Services::course_links()->links( $course_id ) : Services::course_links()->linked_from( $course_id ) as $link ) {
			if ( LinkKind::CONTINUES === $link['kind'] ) {
				$candidate[] = (int) ( $forward ? $link['linked_id'] : $link['course_id'] );
			}
		}
		$trail = Services::category_resolver()->trail_for_object( ObjectType::COURSE, $course_id, $lang );
		$node  = array() === $trail ? null : $trail[ count( $trail ) - 1 ];
		if ( null !== $node ) {
			$rows = Services::course_catalogue()->page( $user_id, new CatalogueQuery( 1, self::COURSES_MAX, 'category', false, $lang, $node->category->id, true, false ) )->rows;
			$ids  = array();
			foreach ( $rows as $row ) {
				$ids[] = $row->course_id;
				if ( EnrolmentStatus::ACTIVE === $row->enrolment_status ) {
					$takes[ $row->course_id ] = true;
				}
			}
			$at = array_search( $course_id, $ids, true );
			if ( false !== $at ) {
				$candidate = array_merge( $candidate, $forward ? array_slice( $ids, $at + 1 ) : array_reverse( array_slice( $ids, 0, $at ) ) );
			}
		}
		foreach ( array_values( array_unique( $candidate ) ) as $other ) {
			if ( $other === $course_id || $other <= 0 ) {
				continue;
			}
			if ( ! isset( $takes[ $other ] ) && ! Learner::is_enrolled( $user_id, $other ) && null === $gate->staff_access( $user_id, $other ) ) {
				continue;
			}
			$listed = self::listed( $other, $lang );
			$items  = $forward ? $listed['items'] : array_reverse( $listed['items'] );
			foreach ( $items as $entry ) {
				$decision = $gate->can_open_item( $user_id, $entry->id );
				if ( $decision->allowed && AccessReason::PREVIEW !== $decision->reason ) {
					return array(
						'kind'   => 'course',
						'course' => self::course_title( $other, $lang ),
					) + self::step( $entry, $listed['posts'], $lang, true );
				}
			}
		}
		return null;
	}

	private static function course_page( int $course_id, string $lang ): array {
		$post = (int) ( Services::posts()->for_objects( ObjectType::COURSE, array( $course_id ), $lang )[ $course_id ] ?? 0 );
		$url  = $post > 0 ? (string) get_permalink( $post ) : '';
		return array(
			'kind'      => 'course_page',
			'item_id'   => 0,
			'course_id' => $course_id,
			'url'       => $url,
			'title'     => self::course_title( $course_id, $lang ),
			'course'    => '',
			'open'      => '' !== $url,
			'reason'    => '',
			'needs'     => false,
			'waits'     => false,
		);
	}

	private static function step( Item $entry, array $posts, string $lang, bool $open ): array {
		$title = wp_strip_all_tags( Services::posts()->title( (int) ( $posts[ $entry->unit_id ] ?? 0 ) ) );
		return array(
			'kind'      => 'item',
			'item_id'   => $entry->id,
			'course_id' => $entry->course_id,
			'url'       => $open ? Urls::item_url( $entry->course_id, $entry->id, $lang ) : '',
			'title'     => '' !== trim( $title ) ? $title : __( '(no title)', 'rooster-lms' ),
			'course'    => '',
			'open'      => $open,
			'reason'    => '',
			'needs'     => false,
			'waits'     => false,
		);
	}

	private static function listed( int $course_id, string $lang ): array {
		$outline  = Learner::outline( $course_id );
		$unit_ids = array_values( array_unique( array_map( static fn( Item $entry ): int => $entry->unit_id, $outline->items ) ) );
		$posts    = array() === $unit_ids ? array() : array_map( 'intval', Services::posts()->for_objects( ObjectType::UNIT, $unit_ids, $lang ) );
		return array(
			'items' => array_values( array_filter( $outline->items, static fn( Item $entry ): bool => ( $posts[ $entry->unit_id ] ?? 0 ) > 0 ) ),
			'posts' => $posts,
		);
	}

	private static function course_title( int $course_id, string $lang ): string {
		$post  = (int) ( Services::posts()->for_objects( ObjectType::COURSE, array( $course_id ), $lang )[ $course_id ] ?? 0 );
		$title = $post > 0 ? wp_strip_all_tags( get_the_title( $post ) ) : '';
		return '' !== trim( $title ) ? $title : __( '(no title)', 'rooster-lms' );
	}
}