<?php

namespace Webkul\BagistoApi\State;

use ApiPlatform\Laravel\Eloquent\Paginator;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\Pagination\Pagination;
use ApiPlatform\State\ProviderInterface;
use Illuminate\Pagination\LengthAwarePaginator;
use Webkul\BagistoApi\Models\ProductQuestion;
use Webkul\BagistoApi\Models\ProductQuestionAnswer;

class ProductQuestionProvider implements ProviderInterface
{
    public function __construct(
        private readonly Pagination $pagination
    ) {}

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): object|array|null
    {
        $args = $context['args'] ?? [];
        $request = request();

        $query = ProductQuestion::query();

        // Filter by product_id from URI variables (nested route) or query param
        $productId = $uriVariables['productId'] ?? $args['product_id'] ?? $request->query('product_id');
        if ($productId) {
            $query->where('product_id', (int) $productId);
        }

        // Storefront shows only approved questions by default
        $status = $args['status'] ?? $request->query('status', 'approved');
        $query->where('status', $status);

        $query->with(['customer']);
        $query->orderByDesc('created_at');

        // ---------------------------------------------------------------
        // Embedded answers options
        // with_answers=true (default)  → embed top N answers per question
        // answers_per_question=5       → how many answers to embed (max 20)
        // answer_status=approved       → which answer status to embed
        // ---------------------------------------------------------------
        $withAnswers = filter_var(
            $args['with_answers'] ?? $request->query('with_answers', 'true'),
            FILTER_VALIDATE_BOOLEAN
        );
        $answersPerQuestion = min(20, max(1, (int) (
            $args['answers_per_question'] ?? $request->query('answers_per_question', 5)
        )));
        $answerStatus = $args['answer_status'] ?? $request->query('answer_status', 'approved');

        // REST pagination
        $page = max(1, (int) ($request->query('page', 1)));
        $perPage = min(50, max(1, (int) ($request->query('per_page', $request->query('limit', 30)))));

        // GraphQL cursor pagination
        $first = isset($args['first']) ? (int) $args['first'] : null;
        $last = isset($args['last']) ? (int) $args['last'] : null;
        $after = $args['after'] ?? null;
        $before = $args['before'] ?? null;

        if ($first || $last || $after || $before) {
            $perPage = $first ?? $last ?? 30;
            $offset = 0;

            if ($after) {
                $decoded = base64_decode($after, true);
                $offset = ctype_digit((string) $decoded) ? ((int) $decoded + 1) : 0;
            }

            if ($before) {
                $decoded = base64_decode($before, true);
                $cursor = ctype_digit((string) $decoded) ? (int) $decoded : 0;
                $offset = max(0, $cursor - $perPage);
            }

            $total = (clone $query)->count();
            $items = $query->offset($offset)->limit($perPage)->get();
            $currentPage = $total > 0 ? (int) floor($offset / $perPage) + 1 : 1;
        } else {
            $total = (clone $query)->count();
            $offset = ($page - 1) * $perPage;
            $items = $query->offset($offset)->limit($perPage)->get();
            $currentPage = $page;
        }

        // Attach answers preview to each question in a single batch query (no N+1)
        if ($withAnswers && $items->isNotEmpty()) {
            $this->attachAnswersPreview($items, $answersPerQuestion, $answerStatus);
        } else {
            $items->each(function ($question) {
                $question->setAttribute('answers_preview', []);
                $question->setAttribute('answers_meta', [
                    'total'        => $question->answers_count,
                    'has_more'     => false,
                    'page_size'    => 0,
                ]);
            });
        }

        return new Paginator(
            new LengthAwarePaginator(
                $items,
                $total,
                $perPage,
                $currentPage,
                ['path' => request()->url()]
            )
        );
    }

    /**
     * Load top N answers for all questions in one query, group by question_id,
     * and attach as `answers_preview` + `answers_meta` attributes.
     *
     * Sort order: pinned first → useful_count desc → newest first.
     * This avoids N+1 — only one extra DB query for the whole page.
     */
    private function attachAnswersPreview(
        \Illuminate\Support\Collection $questions,
        int $limit,
        string $status
    ): void {
        $questionIds = $questions->pluck('id')->toArray();

        // Fetch enough rows to let us take $limit per question after grouping.
        // We over-fetch by $limit × question count so we can slice in PHP.
        $answers = ProductQuestionAnswer::whereIn('question_id', $questionIds)
            ->where('status', $status)
            ->orderByDesc('is_pinned')
            ->orderByDesc('useful_count')
            ->orderByDesc('created_at')
            ->get(['id', 'question_id', 'customer_id', 'customer_name', 'answer',
                   'status', 'is_pinned', 'useful_count', 'created_at', 'updated_at']);

        // Total counts per question (separate lightweight query)
        $totalCounts = ProductQuestionAnswer::whereIn('question_id', $questionIds)
            ->where('status', $status)
            ->groupBy('question_id')
            ->selectRaw('question_id, COUNT(*) as cnt')
            ->pluck('cnt', 'question_id');

        // Group and slice to top N per question
        $grouped = $answers->groupBy('question_id')
            ->map(fn ($group) => $group->take($limit)->values());

        $questions->each(function ($question) use ($grouped, $totalCounts, $limit) {
            $preview = $grouped->get($question->id, collect());
            $total   = (int) ($totalCounts->get($question->id, 0));

            $question->setAttribute('answers_preview', $preview->toArray());
            $question->setAttribute('answers_meta', [
                'total'     => $total,
                'has_more'  => $total > $limit,
                'page_size' => $limit,
            ]);
        });
    }
}