<?php

namespace RoosterLMS\CourseBuilder\Lessons;

use RoosterLMS\Content\CurriculumLayout;
use RoosterLMS\Content\Placement;
use RoosterLMS\Data\Transaction;
use RoosterLMS\Domain\Actor;
use RoosterLMS\Domain\DomainError;
use RoosterLMS\Domain\ErrorCode;
use RoosterLMS\Domain\Services;

defined( 'ABSPATH' ) || exit;

final class Placer {

	public static function place( int $course_id, array $unit_ids, int $section_id, int $position, string $rev, Actor $actor, string &$stale = '' ): array {
		$stale = '';
		$found = '';
		$out   = Transaction::run(
			static function () use ( $course_id, $unit_ids, $section_id, $position, $rev, $actor, &$found ): array {
				$curriculum = Services::curriculum();
				$current    = $curriculum->rev_for_update( $course_id, $actor );
				if ( '' !== $rev && ! hash_equals( $current, $rev ) ) {
					$found = $current;
					return array();
				}
				$placed = $curriculum->add_units( $course_id, $unit_ids, $section_id > 0 ? $section_id : null, $actor );
				self::move_to( $course_id, array_values( $placed ), $section_id, $position, $actor );
				return $placed;
			}
		);
		$stale = $found;
		return $out;
	}

	private static function move_to( int $course_id, array $item_ids, int $section_id, int $position, Actor $actor ): void {
		if ( array() === $item_ids ) {
			return;
		}
		$repo = Services::curriculum_repo();
		$repo->forget();
		$placements = $repo->placements_of_course( $course_id );
		$sections   = array_map( static fn( $s ): int => $s->id, $repo->sections_of_courses( array( $course_id ) )[ $course_id ] ?? array() );
		$moving     = array_flip( $item_ids );
		$others     = array();
		$here       = array();
		$by_section = array();
		foreach ( $placements as $p ) {
			$sid = (int) $p->item->section_id;
			if ( $sid === $section_id && isset( $moving[ $p->item->id ] ) ) {
				$here[ $p->item->id ] = true;
				continue;
			}
			$by_section[ $sid ][] = $p->item->id;
			if ( $sid === $section_id ) {
				$others[] = $p->item->id;
			}
		}
		$position = max( 0, min( $position, count( $others ) ) );
		if ( count( $others ) === $position ) {
			return;
		}
		$ordered                   = array_values( array_filter( $item_ids, static fn( int $id ): bool => isset( $here[ $id ] ) ) );
		$by_section[ $section_id ] = array_merge( array_slice( $others, 0, $position ), $ordered, array_slice( $others, $position ) );
		$entries                   = array();
		foreach ( array_merge( array( 0 ), $sections ) as $sid ) {
			foreach ( $by_section[ $sid ] ?? array() as $id ) {
				$entries[] = array(
					'item_id'    => $id,
					'section_id' => 0 === $sid ? null : $sid,
				);
			}
		}
		if ( count( $entries ) !== count( $placements ) ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => 'position' ) );
		}
		Services::curriculum()->apply_layout( $course_id, new CurriculumLayout( $sections, $entries ), $actor );
	}
}