<?php

namespace App\Services\Upload;

use Illuminate\Http\UploadedFile;
use Illuminate\Support\Str;
use RuntimeException;

/** Bit-sized upload sessions (init → chunks → finalize), matching hosting file manager. */
class ChunkedUploadService
{
    public function baseDir(): string
    {
        $dir = (string) config('transfer.chunk_upload.path', storage_path('app/chunked_uploads'));

        if (! is_dir($dir)) {
            mkdir($dir, 0755, true);
        }

        return $dir;
    }

    /** @param  array<string, mixed>  $metadata */
    public function init(string $ownerKey, array $metadata): string
    {
        $uploadId = (string) Str::uuid();
        $tempDir = $this->sessionDir($uploadId);

        if (! is_dir($tempDir)) {
            mkdir($tempDir, 0755, true);
        }

        $payload = array_merge($metadata, [
            'owner_key' => $ownerKey,
            'chunks_received' => [],
            'created_at' => now()->toIso8601String(),
        ]);

        $this->writeMetadata($uploadId, $payload);

        return $uploadId;
    }

    public function receiveChunk(string $uploadId, string $ownerKey, int $chunkIndex, UploadedFile $chunk, int $expectedSize): int
    {
        $metadata = $this->metadata($uploadId, $ownerKey);
        $tempDir = $this->sessionDir($uploadId);

        $actualSize = (int) $chunk->getSize();
        if ($expectedSize > 0 && $actualSize !== $expectedSize) {
            throw new RuntimeException("Chunk size mismatch: expected {$expectedSize}, got {$actualSize}.");
        }

        $chunkPath = "{$tempDir}/chunk_{$chunkIndex}";
        $chunk->move($tempDir, "chunk_{$chunkIndex}");

        if (! file_exists($chunkPath) || filesize($chunkPath) !== $actualSize) {
            throw new RuntimeException('Chunk save failed.');
        }

        $metadata['chunks_received'][] = $chunkIndex;
        $metadata['chunks_received'] = array_values(array_unique($metadata['chunks_received']));
        sort($metadata['chunks_received']);
        $this->writeMetadata($uploadId, $metadata);

        return count($metadata['chunks_received']);
    }

    /** @return array{path: string, filename: string, size: int, metadata: array<string, mixed>} */
    public function finalize(string $uploadId, string $ownerKey, int $totalChunks): array
    {
        $metadata = $this->metadata($uploadId, $ownerKey);
        $tempDir = $this->sessionDir($uploadId);

        if (count($metadata['chunks_received']) !== $totalChunks) {
            throw new RuntimeException(
                'Missing chunks. Expected '.$totalChunks.', received '.count($metadata['chunks_received']).'.',
            );
        }

        $finalPath = "{$tempDir}/final_".Str::random(8);
        $finalFile = fopen($finalPath, 'wb');
        if ($finalFile === false) {
            throw new RuntimeException('Could not create assembled file.');
        }

        for ($i = 0; $i < $totalChunks; $i++) {
            $chunkPath = "{$tempDir}/chunk_{$i}";
            if (! file_exists($chunkPath)) {
                fclose($finalFile);
                throw new RuntimeException("Chunk {$i} is missing.");
            }

            $chunkHandle = fopen($chunkPath, 'rb');
            if ($chunkHandle === false) {
                fclose($finalFile);
                throw new RuntimeException("Could not read chunk {$i}.");
            }

            while (! feof($chunkHandle)) {
                $buffer = fread($chunkHandle, 8192);
                if ($buffer === false) {
                    break;
                }
                fwrite($finalFile, $buffer);
            }
            fclose($chunkHandle);
        }
        fclose($finalFile);

        $combinedSize = (int) filesize($finalPath);
        $expectedSize = (int) ($metadata['filesize'] ?? 0);
        if ($expectedSize > 0 && abs($combinedSize - $expectedSize) > 1024) {
            @unlink($finalPath);
            throw new RuntimeException("File size mismatch. Expected {$expectedSize} bytes, got {$combinedSize} bytes.");
        }

        $metadata['assembled_path'] = $finalPath;
        $metadata['assembled_size'] = $combinedSize;
        $this->writeMetadata($uploadId, $metadata);

        return [
            'path' => $finalPath,
            'filename' => basename((string) ($metadata['filename'] ?? 'upload.bin')),
            'size' => $combinedSize,
            'metadata' => $metadata,
        ];
    }

    public function toUploadedFile(string $uploadId, string $ownerKey): UploadedFile
    {
        $metadata = $this->metadata($uploadId, $ownerKey);
        $path = (string) ($metadata['assembled_path'] ?? '');

        if ($path === '' || ! is_file($path)) {
            throw new RuntimeException('Assembled upload is not ready.');
        }

        return new UploadedFile(
            $path,
            basename((string) ($metadata['filename'] ?? 'upload.bin')),
            null,
            null,
            true,
        );
    }

    public function cleanup(string $uploadId): void
    {
        $tempDir = $this->sessionDir($uploadId);
        if (! is_dir($tempDir)) {
            return;
        }

        foreach (glob("{$tempDir}/*") ?: [] as $file) {
            @unlink($file);
        }
        @rmdir($tempDir);
    }

    /** @return array<string, mixed> */
    public function metadata(string $uploadId, string $ownerKey): array
    {
        $path = $this->metadataPath($uploadId);
        if (! file_exists($path)) {
            throw new RuntimeException('Upload session not found or expired.');
        }

        $metadata = json_decode((string) file_get_contents($path), true);
        if (! is_array($metadata) || ($metadata['owner_key'] ?? '') !== $ownerKey) {
            throw new RuntimeException('Upload session not found or unauthorized.');
        }

        return $metadata;
    }

    private function sessionDir(string $uploadId): string
    {
        return $this->baseDir().'/'.$uploadId;
    }

    private function metadataPath(string $uploadId): string
    {
        return $this->sessionDir($uploadId).'/metadata.json';
    }

    /** @param  array<string, mixed>  $metadata */
    private function writeMetadata(string $uploadId, array $metadata): void
    {
        file_put_contents($this->metadataPath($uploadId), json_encode($metadata));
    }
}