<?php

declare(strict_types=1);

namespace App\Libraries;

use Exception;

/**
 * Client for the upstream SGK books API, with MongoDB catalog cache.
 */
class BookApi
{
    /** Recursively remove a directory tree (contents + dir). */
    public static function rrmdir(string $dir): void
    {
        $items = glob($dir . '/*') ?: [];
        foreach ($items as $item) {
            is_dir($item) ? self::rrmdir($item) : @unlink($item);
        }
        @rmdir($dir);
    }

    private string $baseUrl;
    private string $token;

    public function __construct()
    {
        $this->baseUrl = rtrim((string) env('api.baseUrl', ''), '/');
        $this->token   = (string) env('api.token', '');
    }

    /**
     * Fetch catalog, refresh MongoDB cache when stale. Returns array of books.
     */
    public function catalog(bool $forceRefresh = false): array
    {
        $col     = Mongo::col('catalog');
        $cacheTs = $col->findOne(['_id' => 'meta']);

        $ttl = (int) env('api.cacheTtl', 21600);
        $fresh = $cacheTs !== null
            && isset($cacheTs['updatedAt'])
            && ((time() - (int) ((string) $cacheTs['updatedAt'] / 1000)) < $ttl)
            && ($cacheTs['count'] ?? 0) > 0;

        if (! $forceRefresh && $fresh) {
            return $this->sorted($this->queryAll($col));
        }

        $data = $this->request('/api/books');
        $books = $data['books'] ?? [];
        if (empty($books)) {
            // fall back to stale cache rather than nothing
            $stale = $this->queryAll($col);
            if (! empty($stale)) {
                return $this->sorted($stale);
            }
            throw new Exception('Không tải được danh mục sách từ API nguồn.');
        }

        $newSourceUpdatedAt = (string) ($data['updatedAt'] ?? '');
        $oldSourceUpdatedAt = (string) ($cacheTs['sourceUpdatedAt'] ?? '');
        $mediaVersion       = (string) ($cacheTs['mediaVersion'] ?? '');

        // upstream data changed → purge local cover cache + thumbs, bump version
        // so Cloudflare/browser see covers as new resources (fetched lazily again).
        if ($forceRefresh || $newSourceUpdatedAt !== $oldSourceUpdatedAt) {
            foreach (['covers', 'covers/thumbs'] as $rel) {
                $dir = WRITEPATH . 'cache/' . $rel;
                if (! is_dir($dir)) {
                    continue;
                }
                if ($rel === 'covers/thumbs') {
                    // recursive delete (thumbnails live in {W}x{H} subdirs)
                    self::rrmdir($dir);
                } else {
                    foreach (glob($dir . '/*') ?: [] as $f) {
                        if (is_file($f)) {
                            @unlink($f);
                        }
                    }
                }
            }
            $mediaVersion = (string) time();
        }

        $col->deleteMany(['bookId' => ['$exists' => true]]);
        $docs = [];
        foreach ($books as $b) {
            $docs[] = $this->toDoc($b);
        }
        $col->insertMany($docs);
        $col->updateOne(
            ['_id' => 'meta'],
            ['$set' => [
                'updatedAt'         => new \MongoDB\BSON\UTCDateTime(),
                'count'             => count($docs),
                'sourceUpdatedAt'   => $newSourceUpdatedAt,
                'mediaVersion'      => $mediaVersion,
            ]],
            ['upsert' => true]
        );

        return $this->sorted($this->queryAll($col));
    }

    private function queryAll(\MongoDB\Collection $col): array
    {
        return $col->find(['bookId' => ['$exists' => true]], ['projection' => ['_id' => 0]])->toArray();
    }

    private function sorted(array $books): array
    {
        usort($books, function ($a, $b) {
            $ga = (int) ($a['grade'] ?? 0);
            $gb = (int) ($b['grade'] ?? 0);
            if ($ga !== $gb) {
                return $ga <=> $gb;
            }
            return strcmp((string) ($a['subject'] ?? ''), (string) ($b['subject'] ?? ''))
                ?: strcmp((string) ($a['title'] ?? ''), (string) ($b['title'] ?? ''));
        });
        return $books;
    }

    public function book(string $id): ?array
    {
        foreach ($this->catalog() as $b) {
            if (($b['id'] ?? null) === $id) {
                return $this->docToArray($b);
            }
        }
        return null;
    }

    /**
     * Stream a resource (pdf/cover) from upstream to the client with auth injected.
     */
    public function stream(string $endpoint, string $downloadName = null): void
    {
        $url = $this->baseUrl . $endpoint;
        $ch  = curl_init($url);

        // forward range headers for pdf.js partial requests
        $range = $_SERVER['HTTP_RANGE'] ?? null;

        curl_setopt_array($ch, [
            CURLOPT_HTTPHEADER => array_filter([
                'Authorization: Bearer ' . $this->token,
                $range ? 'Range: ' . $range : null,
            ]),
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_TIMEOUT => 0,
            CURLOPT_CONNECTTIMEOUT => 15,
            CURLOPT_HEADERFUNCTION => function ($ch, $line) use (&$headers) {
                $trim = trim($line);
                foreach (['content-type', 'content-length', 'accept-ranges', 'content-range', 'content-disposition', 'cache-control'] as $h) {
                    if (stripos($trim, $h) === 0) {
                        if ($h === 'content-disposition') {
                            return strlen($line); // we set our own
                        }
                        header($trim);
                    }
                }
                return strlen($line);
            },
            CURLOPT_WRITEFUNCTION => function ($ch, $data) {
                echo $data;
                if (ob_get_level()) {
                    ob_flush();
                }
                flush();
                return strlen($data);
            },
        ]);

        if ($downloadName) {
            header('Content-Disposition: attachment; filename="' . rawurlencode($downloadName) . '"');
        }

        $ok = curl_exec($ch);
        $code = (int) curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        if (! $ok || $code >= 400) {
            http_response_code($ok ? $code : 502);
        }
    }

    /**
     * Download a resource from upstream to a local file. Returns bytes written or false.
     */
    public function fetchToFile(string $endpoint, string $dest): int|false
    {
        $ch = curl_init($this->baseUrl . $endpoint);
        $fp = fopen($dest, 'wb');
        if (! $fp) {
            return false;
        }
        curl_setopt_array($ch, [
            CURLOPT_HTTPHEADER => ['Authorization: Bearer ' . $this->token],
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_TIMEOUT => 60,
            CURLOPT_CONNECTTIMEOUT => 10,
            CURLOPT_FILE => $fp,
        ]);
        curl_exec($ch);
        $code = (int) curl_getinfo($ch, CURLINFO_HTTP_CODE);
        $size = (int) curl_getinfo($ch, CURLINFO_SIZE_DOWNLOAD);
        $type = (string) curl_getinfo($ch, CURLINFO_CONTENT_TYPE);
        curl_close($ch);
        fclose($fp);

        if ($code !== 200 || $size === 0 || ! str_starts_with($type, 'image/')) {
            return false;
        }
        return $size;
    }

    private function request(string $path): array
    {
        $ch = curl_init($this->baseUrl . $path);
        curl_setopt_array($ch, [
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_HTTPHEADER => ['Authorization: Bearer ' . $this->token],
            CURLOPT_FOLLOWLOCATION => true,
            CURLOPT_TIMEOUT => 120,
            CURLOPT_CONNECTTIMEOUT => 15,
        ]);
        $body = curl_exec($ch);
        $code = (int) curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        if ($code !== 200 || ! is_string($body)) {
            throw new Exception("API lỗi HTTP {$code}");
        }

        return json_decode($body, true) ?? throw new Exception('API trả về JSON không hợp lệ.');
    }

    private function toDoc(array $b): array
    {
        $meta = $b['meta'] ?? [];
        return [
            'bookId'  => $b['id'],
            'id'      => $b['id'],
            'title'   => $b['title'] ?? '',
            'grade'   => (string) ($b['grade'] ?? ''),
            'publisher' => $b['publisher'] ?? '',
            'subject' => $b['subject'] ?? '',
            'localFile' => $b['localFile'] ?? null,
            'pdfEndpoint' => $b['pdfEndpoint'] ?? null,
            'coverEndpoint' => $b['coverEndpoint'] ?? null,
            'meta' => [
                'authors' => $meta['authors'] ?? null,
                'publisherFull' => $meta['publisherFull'] ?? null,
                'pages' => $meta['pages'] ?? null,
                'sizeMB' => $meta['sizeMB'] ?? null,
                'isbn' => $meta['isbn'] ?? null,
                'price' => $meta['price'] ?? null,
                'pdfVersion' => $meta['pdfVersion'] ?? null,
                'creationDate' => $meta['creationDate'] ?? null,
                'cover' => $meta['cover'] ?? null,
                'coverSource' => $meta['coverSource'] ?? null,
            ],
            'search' => mb_strtolower(($b['title'] ?? '') . ' ' . ($b['subject'] ?? '') . ' ' . ($b['publisher'] ?? '')),
        ];
    }

    private function docToArray(array|object $doc): array
    {
        $doc = (array) $doc;
        if (isset($doc['meta']) && is_object($doc['meta'])) {
            $doc['meta'] = (array) $doc['meta'];
        }
        unset($doc['_id']);
        return $doc;
    }
}