<?php

namespace App\Services;

use App\Models\Setting;
use App\Models\Share;
use App\Models\ShareFile;
use Illuminate\Database\Eloquent\ModelNotFoundException;
use Illuminate\Http\UploadedFile;
use Illuminate\Support\Facades\Hash;
use Illuminate\Support\Facades\Storage;
use Illuminate\Support\Str;
use Illuminate\Validation\ValidationException;
use InvalidArgumentException;
use League\MimeTypeDetection\FinfoMimeTypeDetector;
use RuntimeException;

/**
 * A share's life: files registered into a pending share, their encrypted chunks stored as the
 * uploader's browser sends them, and the share completed with its options.
 */
class ShareService
{
    public function __construct(
        private FileEncryptionService $encryptionService,
    ) {}

    /**
     * Register a file the uploader's browser is about to send, in the given pending share or in a
     * new one, and write its encrypted file's header.
     *
     * @throws ValidationException when the file breaks an admin limit
     */
    public function registerFile(?Share $pendingShare, string $name, int $size, ?string $relativePath): ShareFile
    {
        $maxFileSize = (int) Setting::get('max_file_size', 100 * 1024 * 1024);
        $maxFilesPerShare = (int) Setting::get('max_files_per_share', 50);
        $maxSizePerShare = (int) Setting::get('max_size_per_share', 2 * 1024 * 1024 * 1024);

        if ($name === '' || mb_strlen($name) > 255 || $size < 0) {
            $this->rejectFile(__('The file could not be added.'));
        }

        if ($size > $maxFileSize) {
            $this->rejectFile(__('":name" is too large (:size MB). Maximum file size is :max MB.', [
                'name' => $name,
                'size' => round($size / (1024 * 1024), 1),
                'max' => intdiv($maxFileSize, 1024 * 1024),
            ]));
        }

        if ($pendingShare && $pendingShare->files()->count() >= $maxFilesPerShare) {
            $this->rejectFile(__('Too many files. Maximum :max files allowed per share.', ['max' => $maxFilesPerShare]));
        }

        if (($pendingShare?->total_size ?? 0) + $size > $maxSizePerShare) {
            $this->rejectFile(__('Total file size exceeds the maximum allowed per share.'));
        }

        if ($this->getTotalUsedSpace() + $size > $this->getMaxStorageQuota()) {
            $this->rejectFile(__('Storage is full. Please contact the administrator.'));
        }

        $share = $pendingShare ?? Share::query()->create([
            'token' => $this->generateUniqueToken(),
            'encryption_key' => $this->encryptionService->generateRandomKey(),
            'total_size' => 0,
        ]);

        $storedName = Str::uuid().'.enc';

        Storage::disk('shares')->makeDirectory($share->token);
        Storage::disk('shares')->put($share->token.'/'.$storedName, $this->encryptionService->createHeader((int) config('uploads.chunk_size')));

        $file = $share->files()->create([
            'original_name' => $name,
            'relative_path' => $this->sanitizeRelativePath($relativePath),
            'stored_path' => 'shares/'.$share->token.'/'.$storedName,
            'file_size' => $size,
        ]);

        $share->increment('total_size', $size);

        return $file;
    }

    /**
     * Verify the encrypted chunk that comes next for a file and write it into place; returns how
     * many of the file's chunks are stored. The plaintext only exists in memory, to be checked.
     *
     * @throws InvalidArgumentException when the chunk has the wrong length or fails authentication
     * @throws ModelNotFoundException when the file was removed meanwhile
     */
    public function storeChunk(ShareFile $file, int $index, string $chunk): int
    {
        $share = $file->share;
        $handle = @fopen($this->storedFilePath($file), 'r+b');

        if ($handle === false) {
            throw (new ModelNotFoundException)->setModel(ShareFile::class, [$file->id]);
        }

        try {
            ['chunkSize' => $chunkSize, 'noncePrefix' => $noncePrefix] = $this->encryptionService->parseHeader(
                (string) fread($handle, FileEncryptionService::HEADER_LENGTH),
            );

            $chunkCount = $this->encryptionService->chunkCount($file->file_size, $chunkSize);
            $isLast = $index === $chunkCount - 1;

            if ($index >= $chunkCount) {
                throw new InvalidArgumentException('Chunk '.$index.' is beyond the end of the file');
            }

            $plaintextLength = $isLast ? $file->file_size - $index * $chunkSize : $chunkSize;

            if (strlen($chunk) !== $plaintextLength + FileEncryptionService::TAG_LENGTH) {
                throw new InvalidArgumentException('Chunk '.$index.' has the wrong length');
            }

            try {
                $plaintext = $this->encryptionService->decryptChunk($chunk, $share->encryption_key, $noncePrefix, $index, $isLast);
            } catch (RuntimeException) {
                throw new InvalidArgumentException('Chunk '.$index.' failed authentication');
            }

            $mimeType = $index === 0
                ? ((new FinfoMimeTypeDetector)->detectMimeType($file->original_name, $plaintext) ?? 'application/octet-stream')
                : $file->mime_type;

            unset($plaintext);

            if (fseek($handle, $this->encryptionService->chunkOffset($index, $chunkSize)) !== 0
                || fwrite($handle, $chunk) !== strlen($chunk)
                || ! fflush($handle)) {
                throw new RuntimeException('Cannot write chunk '.$index.' of file '.$file->id);
            }
        } finally {
            fclose($handle);
        }

        // Counted only once, even when a retry of the same chunk raced this request.
        $stored = ShareFile::query()
            ->whereKey($file->id)
            ->where('uploaded_chunks', $index)
            ->update([
                'uploaded_chunks' => $index + 1,
                'mime_type' => $mimeType,
                'completed_at' => $isLast ? now() : null,
            ]);

        if ($stored === 0) {
            return ShareFile::query()->findOrFail($file->id)->uploaded_chunks;
        }

        $share->touch();

        return $index + 1;
    }

    /**
     * Remove a file from a pending share, whether or not its upload finished.
     */
    public function removeFile(ShareFile $file): void
    {
        Storage::disk('shares')->delete($file->share->token.'/'.basename($file->stored_path));

        $file->share->decrement('total_size', $file->file_size);
        $file->delete();
    }

    /**
     * Complete a pending share once every file has arrived: with a password the data key is
     * wrapped and no longer stored as it is.
     *
     * @param  array{password?: string|null, expires_at?: mixed, max_downloads?: int|null}  $options
     *
     * @throws ValidationException when files are missing, unfinished or break an admin limit
     */
    public function completeShare(Share $share, array $options = []): Share
    {
        $files = $share->files()->get();
        $maxFilesPerShare = (int) Setting::get('max_files_per_share', 50);
        $maxSizePerShare = (int) Setting::get('max_size_per_share', 2 * 1024 * 1024 * 1024);

        if ($files->isEmpty()) {
            $this->rejectFile(__('Please select at least one file to upload.'));
        }

        if ($files->contains(fn (ShareFile $file): bool => $file->completed_at === null)) {
            $this->rejectFile(__('Wait until every file has finished uploading, or remove the ones that failed.'));
        }

        if ($files->count() > $maxFilesPerShare) {
            $this->rejectFile(__('Too many files. Maximum :max files allowed per share.', ['max' => $maxFilesPerShare]));
        }

        if ($files->sum('file_size') > $maxSizePerShare) {
            $this->rejectFile(__('Total file size exceeds the maximum allowed per share.'));
        }

        $password = $options['password'] ?? null;

        $share->update([
            'password' => $password ? Hash::make($password) : null,
            'wrapped_key' => $password ? $this->encryptionService->wrapKey($share->encryption_key, $password) : null,
            'encryption_key' => $password ? null : $share->encryption_key,
            'expires_at' => $options['expires_at'] ?? null,
            'max_downloads' => $options['max_downloads'] ?? null,
            'total_size' => $files->sum('file_size'),
            'completed_at' => now(),
        ]);

        return $share;
    }

    /**
     * Create a share from files already on the server, through the same steps an upload from the
     * browser takes. Used by tests and demo data.
     *
     * @param  array<int, array{file: UploadedFile, relativePath: string|null}>  $files
     * @param  array{password?: string|null, expires_at?: mixed, max_downloads?: int|null}  $options
     */
    public function createShare(array $files, array $options = []): Share
    {
        $share = null;

        foreach ($files as $fileData) {
            $file = $fileData['file'];
            $shareFile = $this->registerFile($share, $file->getClientOriginalName(), $file->getSize(), $fileData['relativePath'] ?? null);
            $share = $shareFile->share;

            $header = $this->readHeader($shareFile);
            $source = fopen($file->getRealPath(), 'rb');

            for ($index = 0; $index < $header['chunkCount']; $index++) {
                $plaintextLength = min($header['chunkSize'], $shareFile->file_size - $index * $header['chunkSize']);

                // A fake upload reports a size its content does not have: zeros make up the rest.
                $chunk = $this->encryptionService->encryptChunk(
                    str_pad($plaintextLength > 0 ? (string) fread($source, $plaintextLength) : '', $plaintextLength, "\0"),
                    $share->encryption_key,
                    $header['noncePrefix'],
                    $index,
                    $index === $header['chunkCount'] - 1,
                );

                $this->storeChunk($shareFile->refresh(), $index, $chunk);
            }

            fclose($source);
        }

        if ($share === null) {
            $this->rejectFile(__('Please select at least one file to upload.'));
        }

        return $this->completeShare($share, $options);
    }

    /**
     * Generate a unique share token with retry on collision.
     */
    private function generateUniqueToken(): string
    {
        for ($i = 0; $i < 5; $i++) {
            $token = Str::random(16);

            if (! Share::query()->where('token', $token)->exists()) {
                return $token;
            }
        }

        throw new RuntimeException('Unable to generate a unique share token');
    }

    /**
     * Delete a share and its files from disk.
     */
    public function deleteShare(Share $share): void
    {
        Storage::disk('shares')->deleteDirectory($share->token);

        $share->delete();
    }

    /**
     * Get the decryption key for a share: unwrapped with the password, derived from it for shares
     * created before key wrapping, or stored for shares without a password.
     */
    public function getDecryptionKey(Share $share, ?string $password = null): string
    {
        if ($share->isPasswordProtected()) {
            if (! $password) {
                throw new RuntimeException('Password required for this share');
            }

            if ($share->wrapped_key !== null) {
                return $this->encryptionService->unwrapKey($share->wrapped_key, $password);
            }

            return bin2hex($this->encryptionService->deriveKey($password, $share->encryption_salt));
        }

        return $share->encryption_key;
    }

    /**
     * Verify a password against a share's stored hash.
     */
    public function verifyPassword(Share $share, string $password): bool
    {
        if (! $share->isPasswordProtected()) {
            return true;
        }

        return Hash::check($password, $share->password);
    }

    /**
     * Record a download and auto-delete if limit reached.
     */
    public function recordDownload(Share $share): void
    {
        $share->increment('download_count');

        if ($share->hasReachedDownloadLimit()) {
            $this->deleteShare($share);
        }
    }

    /**
     * Get total used space in bytes, files still being uploaded included.
     */
    public function getTotalUsedSpace(): int
    {
        return (int) Share::query()->sum('total_size');
    }

    /**
     * Check if storage is full based on admin-configured max quota.
     */
    public function isStorageFull(): bool
    {
        return $this->getTotalUsedSpace() >= $this->getMaxStorageQuota();
    }

    /**
     * Get the maximum storage quota in bytes.
     */
    public function getMaxStorageQuota(): int
    {
        return (int) Setting::get('max_storage_quota', 20 * 1024 * 1024 * 1024);
    }

    /**
     * A registered file's chunk size, nonce prefix and chunk count, from its encrypted file's header.
     *
     * @return array{chunkSize: int, noncePrefix: string, chunkCount: int}
     */
    public function readHeader(ShareFile $file): array
    {
        $header = $this->encryptionService->parseHeader(
            (string) file_get_contents($this->storedFilePath($file), false, null, 0, FileEncryptionService::HEADER_LENGTH),
        );

        return [...$header, 'chunkCount' => $this->encryptionService->chunkCount($file->file_size, $header['chunkSize'])];
    }

    /**
     * Where a file's encrypted content is stored on disk.
     */
    public function storedFilePath(ShareFile $file): string
    {
        return Storage::disk('shares')->path($file->share->token.'/'.basename($file->stored_path));
    }

    /**
     * A relative path from a dropped folder, or null when it could reach outside the share.
     */
    private function sanitizeRelativePath(?string $relativePath): ?string
    {
        if ($relativePath === null) {
            return null;
        }

        $relativePath = str_replace('\\', '/', $relativePath);

        if (str_starts_with($relativePath, '/') || str_contains($relativePath, '..')) {
            return null;
        }

        return $relativePath;
    }

    /**
     * @throws ValidationException
     */
    private function rejectFile(string $message): never
    {
        throw ValidationException::withMessages(['files' => $message]);
    }
}