import Combine
import Foundation
import R2Shared

struct HTTPDownload {
  let file: URL
  let response: HTTPResponse
}

extension HTTPClient {

  func fetch(_ request: HTTPRequestConvertible) -> AnyPublisher<HTTPResponse, HTTPError> {
    var cancellable: R2Shared.Cancellable? = nil
    return Future { promise in
      cancellable = self.fetch(request, completion: promise)
    }
    .handleEvents(receiveCancel: { cancellable?.cancel() })
    .eraseToAnyPublisher()
  }

  func download(_ request: HTTPRequestConvertible, progress: @escaping (Double) -> Void) -> AnyPublisher<HTTPDownload, HTTPError> {
    openTemporaryFileForWriting()
      .flatMap { (destination, handle) -> AnyPublisher<HTTPDownload, HTTPError> in
        var cancellable: R2Shared.Cancellable? = nil

        return Future { promise in
          cancellable = self.stream(request,
            consume: { data, progression in
              if let progression = progression {
                progress(progression)
              }
              handle.write(data)
            },
            completion: { result in
              do {
                try handle.close()
                promise(.success(HTTPDownload(file: destination, response: try result.get())))
              } catch {
                try? FileManager.default.removeItem(at: destination)
                promise(.failure(HTTPError(error: error)))
              }
            })
        }
        .handleEvents(receiveCancel: {
          cancellable?.cancel()
          try? handle.close()
          try? FileManager.default.removeItem(at: destination)
        })
        .eraseToAnyPublisher()
      }
      .eraseToAnyPublisher()
  }

  private func openTemporaryFileForWriting() -> AnyPublisher<(URL, FileHandle), HTTPError> {
    Paths.makeTemporaryURL()
      .tryMap { destination in
        // Makes sure the file exists.
        try "".write(to: destination, atomically: true, encoding: .utf8)
        let handle = try FileHandle(forWritingTo: destination)
        return (destination, handle)
      }
      .mapError { HTTPError(kind: .other, cause: $0) }
      .eraseToAnyPublisher()
  }
}