import Foundation

/// Bridges URLSessionDownloadDelegate progress callbacks to Swift concurrency.
/// Each instance manages a single download with real-time progress reporting.
///
/// This is a stub for test-first development. The implementation will be
/// filled in by the fix-download-progress task.
final class ProgressDownloader: NSObject, URLSessionDownloadDelegate, Sendable {

    /// Result of a completed download.
    struct Result: Sendable {
        let fileURL: URL
        let response: HTTPURLResponse
    }

    /// Download a file with progress reporting.
    ///
    /// - Parameters:
    ///   - request: The URLRequest to download.
    ///   - sessionConfiguration: URLSession configuration (injectable for testing).
    ///   - onProgress: Called on each progress update (0.0-1.0). Called on arbitrary thread.
    /// - Returns: The temporary file URL and HTTP response.
    static func download(
        request: URLRequest,
        sessionConfiguration: URLSessionConfiguration = .default,
        onProgress: @escaping @Sendable (Double) -> Void
    ) async throws -> Result {
        // STUB: To be implemented by fix-download-progress task.
        // This stub exists so that tests compile in the write-tests phase.
        fatalError("ProgressDownloader.download not yet implemented")
    }

    // MARK: - URLSessionDownloadDelegate (stubs)

    func urlSession(
        _ session: URLSession,
        downloadTask: URLSessionDownloadTask,
        didFinishDownloadingTo location: URL
    ) {
        fatalError("Not yet implemented")
    }

    func urlSession(
        _ session: URLSession,
        downloadTask: URLSessionDownloadTask,
        didWriteData bytesWritten: Int64,
        totalBytesWritten: Int64,
        totalBytesExpectedToWrite: Int64
    ) {
        fatalError("Not yet implemented")
    }

    func urlSession(
        _ session: URLSession,
        task: URLSessionTask,
        didCompleteWithError error: (any Error)?
    ) {
        fatalError("Not yet implemented")
    }
}