<?php

namespace App\Element\UseCases\ReorderChildElements;

use App\Element\Element;
use App\Element\ElementRepository;
use App\Exceptions\BadRequestException;
use App\Exceptions\NotFoundException;

class ReorderChildElements
{
    public function __construct(private ElementRepository $elementRepository)
    {
    }

    /**
     * @return Element[]
     * @throws BadRequestException
     * @throws NotFoundException
     */
    public function execute(ReorderChildElementsRequest $request): array
    {
        if ($request->parentElementId === null) {
            throw new BadRequestException('parentElementId is required');
        }

        if ($request->childElementIds === null) {
            throw new BadRequestException('childElementIds is required');
        }

        $parentElement = $this->elementRepository->find(
            $request->parentElementId,
        );
        if ($parentElement === null) {
            throw new NotFoundException('Parent element not found');
        }

        $childElementIds = $this->validatedChildElementIds(
            $request->childElementIds,
        );
        $directChildElementIds = $this->elementIds(
            $this->elementRepository->findByParentElement($parentElement),
        );

        $this->validateNoDuplicateIds($childElementIds);
        $this->validateAllIdsAreDirectChildren(
            $childElementIds,
            $directChildElementIds,
        );
        $this->validateEveryDirectChildWasSubmitted(
            $childElementIds,
            $directChildElementIds,
        );

        return $this->elementRepository->reorderChildren(
            $parentElement,
            $childElementIds,
        );
    }

    /**
     * @param mixed[] $childElementIds
     * @return int[]
     * @throws BadRequestException
     */
    private function validatedChildElementIds(array $childElementIds): array
    {
        $validatedChildElementIds = [];
        foreach ($childElementIds as $childElementId) {
            if (! is_int($childElementId)) {
                throw new BadRequestException(
                    'childElementIds must contain integers',
                );
            }

            $validatedChildElementIds[] = $childElementId;
        }

        return $validatedChildElementIds;
    }

    /**
     * @param int[] $childElementIds
     * @throws BadRequestException
     */
    private function validateNoDuplicateIds(array $childElementIds): void
    {
        $seenChildElementIds = [];
        foreach ($childElementIds as $childElementId) {
            if (isset($seenChildElementIds[$childElementId])) {
                throw new BadRequestException(
                    'Child order contains duplicate ids',
                );
            }

            $seenChildElementIds[$childElementId] = true;
        }
    }

    /**
     * @param int[] $childElementIds
     * @param int[] $directChildElementIds
     * @throws BadRequestException
     */
    private function validateAllIdsAreDirectChildren(
        array $childElementIds,
        array $directChildElementIds,
    ): void {
        $directChildElementIdsById = [];
        foreach ($directChildElementIds as $directChildElementId) {
            $directChildElementIdsById[$directChildElementId] = true;
        }

        foreach ($childElementIds as $childElementId) {
            if (! isset($directChildElementIdsById[$childElementId])) {
                throw new BadRequestException(
                    'Child order contains invalid child',
                );
            }
        }
    }

    /**
     * @param int[] $childElementIds
     * @param int[] $directChildElementIds
     * @throws BadRequestException
     */
    private function validateEveryDirectChildWasSubmitted(
        array $childElementIds,
        array $directChildElementIds,
    ): void {
        if (count($childElementIds) === count($directChildElementIds)) {
            return;
        }

        throw new BadRequestException(
            'Child order must include every direct child',
        );
    }

    /**
     * @param Element[] $elements
     * @return int[]
     */
    private function elementIds(array $elements): array
    {
        $elementIds = [];
        foreach ($elements as $element) {
            $elementIds[] = $element->getId();
        }

        return $elementIds;
    }
}