A testable, Promise based example network service

ChatNetworkService.swift

public protocol ChatNetworkService {
  func loadMessages(bookingId: String) -> Promise<[ChatMessage]>
  func sendMessage(_ message: String, bookingId: String) -> Promise<ChatMessage>
}

public final class DefaultChatNetworkService {
  public init() { }
}

extension ChatNetworkService: ChatNetworkService {
  public func loadMessages(bookingId: String) -> Promise<[ChatMessage]> {
    Promise { fullfill, reject in
      Networking.session
        .request(resource: ChatResource.getMessages(bookingId: bookingId))
        .validate()
        .responseDecodable(
          decoder: JSONDecoder.default
        ) { (response: DataResponse<ApiResponseContainer<[ChatMessage]>, AFError>) in
          switch response.result {
          case .success(let container):
            fullfill(container.data)
          case .failure(let error):
            reject(error)
          }
        }
    }
  }

  public func sendMessage(_ message: String, bookingId: String) -> Promise<ChatMessage> {
    Promise { fullfill, reject in
      Networking.session
        .request(
          resource: ChatResource.postMessage(bookingId: bookingId),
          parameters: ChatMessageDTO(content: message)
        )
        .validate()
        .responseDecodable(
          decoder: JSONDecoder.default
        ) { (response: DataResponse<ApiResponseContainer<ChatMessage>, AFError>) in
          switch response.result {
          case .success(let container):
            fullfill(container.data)
          case .failure(let error):
            reject(error)
          }
        }
    }
  }
}