LaunchListViewModel

protocol LaunchListViewModelType {
    var launchViewModels: BehaviorRelay<[LaunchListTableViewCellViewModel]> { get } // 1
    var notifyError: BehaviorRelay<Error?> { get } // 2
    
    func fetchLaunchesWithQuery() // 3
}

class LaunchListViewModel: LaunchListViewModelType { 
    let apiService: APIServiceProtocol // 4
    
    var launchViewModels = BehaviorRelay<[LaunchListTableViewCellViewModel]>(value: []) 
    var notifyError = BehaviorRelay<Error?>(value: nil)
    
    init(apiService: APIServiceProtocol = APIService()) { // 5
        self.apiService = apiService
        fetchLaunchesWithQuery()
    }
    
    func fetchLaunchesWithQuery() {
        apiService.fetchLaunchesWithQuery { [weak self] (launchResponse, error, _) in
            guard let strongSelf = self else { return }
            
            if let launchResponse = launchResponse {
                strongSelf.processFetchedLaunches(launchResponse: launchResponse)
            } else if let error = error {
                strongSelf.notifyError.accept(error)
            }
        }
    }
    
    func processFetchedLaunches(launchResponse: LaunchResponse) { // 6
        guard let launches = launchResponse.docs else { return }
        launchViewModels.accept(convertLaunchesToLaunchListTableViewCellViewModels(launches: launches))
    }
    
    func convertLaunchesToLaunchListTableViewCellViewModels(launches: [Launch]) -> [LaunchListTableViewCellViewModel] { // 7
        var launchListTableViewCellViewModels: [LaunchListTableViewCellViewModel] = []
        for launch in launches {
            launchListTableViewCellViewModels.append(LaunchListTableViewCellViewModel(launch: launch))
        }
        return launchListTableViewCellViewModels
    }
}