<?php

declare(strict_types=1);

namespace App\Service;

use App\Entity\Groups\AdditionalService;

/**
 * Resolves mutually exclusive additional services.
 *
 * Services sharing an exclusion group interact as soon as at least one of the two involved
 * services is flagged as exclusive: selecting the exclusive one clears all other members of
 * the group, selecting any other member clears the exclusive ones. Members that are not
 * exclusive can be combined freely.
 *
 * Conflicts are resolved in favour of the newest selection, determined by diffing the
 * submitted ids against the previously stored ones.
 */
class AdditionalServiceExclusionResolver
{
    /**
     * @param AdditionalService[]   $availableServices
     * @param array<array-key, int> $submittedIds      keys are preserved, grouped radios submit under their group name
     * @param array<array-key, int> $previousIds
     *
     * @return array<array-key, int>
     */
    public function resolve(array $availableServices, array $submittedIds, array $previousIds): array
    {
        $rules = $this->buildRules($availableServices);

        if ([] === $rules) {
            return $submittedIds;
        }

        $added = array_values(array_diff($submittedIds, $previousIds));

        foreach ($added as $addedId) {
            if (!isset($rules[$addedId])) {
                continue;
            }

            $submittedIds = array_filter(
                $submittedIds,
                fn (int $id) => !$this->conflicts($rules, $addedId, $id),
            );
        }

        return $submittedIds;
    }

    /**
     * @param array<int, array{group: string, exclusive: bool}> $rules
     */
    private function conflicts(array $rules, int $a, int $b): bool
    {
        if ($a === $b || !isset($rules[$b])) {
            return false;
        }

        if ($rules[$a]['group'] !== $rules[$b]['group']) {
            return false;
        }

        return $rules[$a]['exclusive'] || $rules[$b]['exclusive'];
    }

    /**
     * @param AdditionalService[] $availableServices
     *
     * @return array<int, array{group: string, exclusive: bool}>
     */
    private function buildRules(array $availableServices): array
    {
        $rules = [];

        foreach ($availableServices as $service) {
            $group = $service->getExclusionGroup();
            $id = $service->getId();

            if (null === $id || null === $group || '' === $group) {
                continue;
            }

            $rules[$id] = ['group' => $group, 'exclusive' => $service->isExclusive()];
        }

        return $rules;
    }
}