<?php

/**
 * Pagination helper - extrakce spolecne logiky pro strankovani seznamu.
 */

declare(strict_types=1);

class PaginationHelper
{
    private const DEFAULT_PER_PAGE = 25;
    private const MAX_PER_PAGE = 500;

    /**
     * Nacte pagination parametry z GET requestu.
     *
     * @return array{page: int, per_page: int, sort: string, order: string, search: string}
     */
    public static function parseParams(array $sortMap, string $defaultSort = 'created_at'): array
    {
        $sort = $_GET['sort'] ?? $defaultSort;
        $order = strtoupper($_GET['order'] ?? 'DESC') === 'ASC' ? 'ASC' : 'DESC';
        $page = max(1, (int) ($_GET['page'] ?? 1));
        $perPage = min(self::MAX_PER_PAGE, max(1, (int) ($_GET['per_page'] ?? self::DEFAULT_PER_PAGE)));
        $search = trim($_GET['search'] ?? '');

        if (!isset($sortMap[$sort])) {
            errorResponse('Neplatný parametr řazení', 400);
        }

        return [
            'page' => $page,
            'per_page' => $perPage,
            'sort' => $sortMap[$sort],
            'order' => $order,
            'search' => $search ? mb_substr($search, 0, 100) : '',
        ];
    }

    /**
     * Spusti COUNT + SELECT dotazy s pagination a vrati vysledek.
     *
     * @param PDO $pdo
     * @param string $countSql - COUNT(*) dotaz
     * @param string $dataSql - SELECT dotaz (bez LIMIT/OFFSET)
     * @param array $params - parametry pro prepared statement
     * @param array{page: int, per_page: int, sort: string, order: string} $pagination
     * @return array{items: array, pagination: array}
     */
    public static function paginate(
        PDO $pdo,
        string $countSql,
        string $dataSql,
        array $params,
        array $pagination
    ): array {
        $page = $pagination['page'];
        $perPage = $pagination['per_page'];

        $stmt = $pdo->prepare($countSql);
        $stmt->execute($params);
        $total = (int) $stmt->fetchColumn();

        $offset = ($page - 1) * $perPage;
        $totalPages = (int) ceil($total / $perPage);

        $sql = "{$dataSql} LIMIT {$perPage} OFFSET {$offset}";
        $stmt = $pdo->prepare($sql);
        $stmt->execute($params);
        $items = $stmt->fetchAll();

        return [
            'items' => $items,
            'pagination' => [
                'total' => $total,
                'page' => $page,
                'per_page' => $perPage,
                'total_pages' => $totalPages,
            ],
        ];
    }
}