Coordinate media experiences with Group Activities

protocol GroupActivity: Codable {

    /// An identifier so the system knows how to reference this activity
    static var activityIdentifier: String { get }

    /// Information that the system uses to show this activity, such as title and a preview image
    var metadata: GroupActivityMetadata { get async }
}

func playButtonTapped() {
    let activity = MovieWatchingActivity(movie: movie)
            
    Task {
        switch await activity.prepareForActivation() {
        case .activationDisabled:
            // Playback coordination isn't active. Queue movie
            // for local playback.
            self.enqueuedMovie = movie
        case .activationPreferred:
            // Activate the activity. The system enqueues the movie
            // when the activity starts.
            activity.activate()
        case .cancelled:
            // The user cancelled the operation. Nothing to perform.
            break
        default:
            break
        }
    }
}

// Receiving a GroupSession from the GroupSession AsyncSequence

func listenForGroupSession() {
    Task {
        for await session in MovieWatchingActivity.sessions() {
            ...
        }
    }
}

let player = AVPlayer()

...

func listenForGroupSession() {
    Task {
        for await groupSession in MovieWatchingActivity.sessions() {
            
            // Verify content is available, prepare for playback to begin

            player.playbackCoordinator.coordinateWithSession(groupSession)

            ...
        }
    }
}

class AVPlaybackCoordinator {
    func beginSuspension(for reason: AVCoordinatedPlaybackSuspension.Reason) -> AVCoordinatedPlaybackSuspension
}

class AVCoordinatedPlaybackSuspension { 	
    func end()
    func end(proposingNewTime newTime: CMTime)
}