<?php

namespace App\Http\Controllers;

use App\Models\Share;
use App\Models\ShareFile;
use App\Services\FileEncryptionService;
use App\Services\ShareService;
use GuzzleHttp\Psr7\PumpStream;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Storage;
use Symfony\Component\HttpFoundation\HeaderUtils;
use Symfony\Component\HttpFoundation\StreamedResponse;
use ZipStream\CompressionMethod;
use ZipStream\OperationMode;
use ZipStream\ZipStream;

class DownloadController extends Controller
{
    public function __construct(
        private FileEncryptionService $encryptionService,
        private ShareService $shareService,
    ) {}

    /**
     * Download all files as a ZIP archive, streamed file by file as it is decrypted: stored without
     * compression, with ZIP64 for files over 4 GB, and never held in memory or written to disk. The
     * archive's size is worked out from the files' sizes first, so the browser shows its progress
     * and notices a download cut short. The private text is left out: it is only ever shown on the
     * page.
     */
    public function download(Request $request, Share $share): StreamedResponse
    {
        abort_if(! $share->isCompleted() || $share->isExpired(), 404);

        $share->load(['files' => fn ($query) => $query->where('is_text', false)]);
        abort_if($share->files->isEmpty(), 404);

        $key = $this->shareService->sessionDecryptionKey($share, $request->session());

        // Counted before the body streams: the session is saved by then.
        abort_unless($this->shareService->claimDownload($share, $request->session()), 404);

        $zip = new ZipStream(
            operationMode: OperationMode::SIMULATE_STRICT,
            defaultCompressionMethod: CompressionMethod::STORE,
            defaultEnableZeroHeader: true,
            sendHttpHeaders: false,
            flushOutput: true,
        );

        foreach ($share->files as $file) {
            $zip->addFileFromCallback(
                fileName: $this->archiveName($file),
                exactSize: $file->file_size,
                callback: fn (): PumpStream => $this->decryptedStream($share, $file, $key),
            );
        }

        $size = $zip->finish();

        return new StreamedResponse(function () use ($zip): void {
            // A large share takes longer than any request limit to send.
            set_time_limit(0);

            $zip->executeSimulation();
        }, 200, [
            'Content-Type' => 'application/zip',
            'Content-Length' => $size,
            'Content-Disposition' => HeaderUtils::makeDisposition('attachment', 'share-'.$share->token.'.zip'),
        ]);
    }

    /**
     * Download a single file; never the private text, which is only ever shown on the page. A
     * `Range` request gets the bytes from where an interrupted download stopped, so the browser,
     * or the page's folder download, resumes it instead of starting over.
     */
    public function downloadFile(Request $request, Share $share, ShareFile $shareFile): StreamedResponse
    {
        abort_if(! $share->isCompleted() || $share->isExpired(), 404);
        abort_if($shareFile->share_id !== $share->id || $shareFile->is_text, 404);

        $key = $this->shareService->sessionDecryptionKey($share, $request->session());

        $size = $shareFile->file_size;
        $etag = '"'.hash('xxh128', $shareFile->stored_path).'"';
        [$start, $end] = $this->requestedRange($request, $size, $etag) ?? [0, $size - 1];

        abort_unless($this->shareService->claimDownload($share, $request->session()), 404);

        $encryptedPath = Storage::disk('shares')->path($share->token.'/'.basename($shareFile->stored_path));
        $partial = $start > 0 || $end < $size - 1;

        $headers = [
            'Content-Type' => $shareFile->mime_type ?? 'application/octet-stream',
            'Content-Disposition' => HeaderUtils::makeDisposition(
                'attachment',
                $shareFile->original_name,
                'download',
            ),
            'Content-Length' => max($end - $start + 1, 0),
            'Accept-Ranges' => 'bytes',
            'ETag' => $etag,
        ];

        if ($partial) {
            $headers['Content-Range'] = "bytes {$start}-{$end}/{$size}";
        }

        return new StreamedResponse(function () use ($encryptedPath, $key, $start, $end): void {
            set_time_limit(0);

            $remaining = $end - $start + 1;

            foreach ($this->encryptionService->decryptedChunks($encryptedPath, $key, $start) as $chunk) {
                if (strlen($chunk) >= $remaining) {
                    echo substr($chunk, 0, $remaining);
                    flush();

                    return;
                }

                echo $chunk;
                flush();
                $remaining -= strlen($chunk);
            }
        }, $partial ? 206 : 200, $headers);
    }

    /**
     * The first and last byte a single `Range` request asks for, or null to send the whole file:
     * without a range, with one this does not read (several ranges, another unit), or with an
     * `If-Range` naming another version of the file. A range wholly past the end is refused.
     *
     * @return array{0: int, 1: int}|null
     */
    private function requestedRange(Request $request, int $size, string $etag): ?array
    {
        $range = (string) $request->header('Range');

        if ($size === 0 || ! preg_match('/^bytes=(\d*)-(\d*)$/', $range, $matches) || $matches[1].$matches[2] === ''
            || ($request->hasHeader('If-Range') && $request->header('If-Range') !== $etag)) {
            return null;
        }

        [$start, $end] = $matches[1] === ''
            ? [max($size - (int) $matches[2], 0), $size - 1]
            : [(int) $matches[1], $matches[2] === '' ? $size - 1 : min((int) $matches[2], $size - 1)];

        abort_if($start > $end, 416, headers: ['Content-Range' => "bytes */{$size}"]);

        return [$start, $end];
    }

    /**
     * A file's decrypted content as a stream ZipStream reads from.
     */
    private function decryptedStream(Share $share, ShareFile $file, string $key): PumpStream
    {
        $chunks = $this->encryptionService->decryptedChunks(
            Storage::disk('shares')->path($share->token.'/'.basename($file->stored_path)),
            $key,
        );

        return new PumpStream(function () use ($chunks): string|false {
            while ($chunks->valid() && $chunks->current() === '') {
                $chunks->next();
            }

            if (! $chunks->valid()) {
                return false;
            }

            $chunk = $chunks->current();
            $chunks->next();

            return $chunk;
        });
    }

    /**
     * A file's path inside the archive: its folder path when it came from a dropped folder, never
     * one that could reach outside the archive.
     */
    private function archiveName(ShareFile $file): string
    {
        $filename = str_replace('\\', '/', $file->relative_path ?: $file->original_name);

        if (str_starts_with($filename, '/') || str_contains($filename, '..')) {
            return basename($filename);
        }

        return $filename;
    }
}