import CallsBroadcastKit
import CoreMedia
import ReplayKit

/// The broadcast upload extension: ReplayKit's frames in, the app's socket
/// out. It links CallsBroadcastKit and nothing else of Calls, and holds
/// one frame buffer, because it lives under a memory ceiling of about
/// fifty megabytes and is killed without a word past it.
///
/// It never talks to the meeting. The app is already in the call and owns
/// every peer connection; this only hands it pictures.
final class SampleHandler: RPBroadcastSampleHandler {
  private var sender: BroadcastSender?

  override func broadcastStarted(withSetupInfo setupInfo: [String: NSObject]?) {
    guard let group = BroadcastPath.appGroup, let path = BroadcastPath.socket(appGroup: group)
    else {
      finish("Calls could not share your screen on this build.")
      return
    }
    let sender = BroadcastSender(path: path)
    // Two seconds: the countdown has just ended, and the app, which is in
    // the call, is listening already. Longer would only delay the answer
    // to someone who started a broadcast with no call to share it to.
    guard sender.connect(timeout: 2) else {
      finish("Join a call in Calls, then share your screen from there.")
      return
    }
    sender.onClosed = { [weak self] in
      self?.finish("You stopped sharing your screen in Calls.")
    }
    self.sender = sender
  }

  override func processSampleBuffer(
    _ sampleBuffer: CMSampleBuffer, with sampleBufferType: RPSampleBufferType
  ) {
    guard sampleBufferType == .video, let sender, let pixels = sampleBuffer.imageBuffer else {
      return
    }
    let orientation =
      (CMGetAttachment(sampleBuffer, key: RPVideoSampleOrientationKey as CFString, attachmentModeOut: nil)
      as? NSNumber)?.uint16Value ?? 1
    let time = CMTimeGetSeconds(sampleBuffer.presentationTimeStamp)
    sender.send(pixels, orientation: orientation, timestampNs: UInt64(max(0, time) * 1_000_000_000))
  }

  override func broadcastFinished() {
    sender?.close()
    sender = nil
  }

  /// Ends the broadcast with a sentence the system shows the person. The
  /// only way an extension can say anything at all.
  private func finish(_ sentence: String) {
    sender?.close()
    sender = nil
    finishBroadcastWithError(
      NSError(domain: "Calls", code: 1, userInfo: [NSLocalizedDescriptionKey: sentence]))
  }
}