remote chats provider for medium article

RemoteChatsProvider.swift

class RemoteChatsProvider: ChatsProvider {
  func getChats(request: GetConversationsRequest) throws -> [Message] {
    var items: [MessageDto] = []
    var outputError: Error? = nil
    let dispatchGroup = DispatchGroup()
    dispatchGroup.enter()
    
    CompanyMessagesAPI.companyMessagesGetConversations(request: request, completion: { (successfulResponse, error) in
      do {
        items = try SwaggerApiResponseHandler.unwrapResponse((successfulResponse, error))
        dispatchGroup.leave()
      } catch let error {
        outputError = error
        dispatchGroup.leave()
      }
    })
    _ = dispatchGroup.wait(timeout: .distantFuture)
    if let error = outputError {
      throw error
    }
    return items.map({ Message(wsInstance: $0) }).compactMap({$0})
  }
  /// etc ...
}