DreamCodeWithPromises.swift

// Promisification of asynchronous code:
func downloadUser() -> Promise<User> {
  return Promise<User> { 
    resolve, reject, cancellation in 
    self.downloadUser() { 
      user in
      resolve(user)
    }
  }
}

func downloadFavouriteMovies(for user: User) -> Promise<[Movie]> {
  return Promise<[Movie]> { 
    resolve, reject, cancellation in 
    self.downloadFavouriteMovies(for: user) { 
      movies in
      resolve(movies)
    }
  }
}

func downloadRatings(for movies: [Movies) -> Promise<[Rating]> {
  return Promise<[Rating]> { 
    resolve, reject, cancellation in 
    self.downloadRatings(for: movies) { 
      ratings in
      resolve(ratings)
    }
  }
}

func downloadFriends(for user: User) -> Promise<[User]> {
  return Promise<[User]> { 
    resolve, reject, cancellation in 
    self.downloadFriends(for: user) { 
      friends in
      resolve(friends)
    }
  }
}

func downloadMovies(for friends: [User]) -> Promise<[Movie]> {
  return Promise<[Movie]> { 
    resolve, reject, cancellation in 
    self.downloadMovies(for: friends) { 
      movies in
      resolve(movies)
    }
  }
}

// usage:
let user = try await(downloadUser())
let movies = try await(downloadFavouriteMovies(for: user))
let ratings = try await(downloadRatings(for: movies)) 
let friends = try await(downloadFriends(for: users))
let friendsMovies = try await(downloadMovies(for: friends))
self.presentProfile(for: user, movies: movies, ratings: ratings, friends: friends, movies: movies)