ResultImplementation

class SimpleListViewModel(application: Application) : ListViewModel(application) {

    private val mutableScreenState = MutableLiveData(
        ListScreenState(null, null, null)
    )
    override val screenState: LiveData<ListScreenState> = mutableScreenState
    override val commandManager: CommandManager<ListScreenState> by lazy {
        CommandManagerImpl(mutableScreenState, viewModelScope)
    }

    init {
        reload()
    }

    override fun reload() {
        commandManager.postCommand(
            RefreshCommand(
                { executeLoadNextPage(0) },
                { UIProgressErrorItem.Progress },
                { UIProgressErrorItem.Error(it.toString()) { reload() } }
            )
        )
    }

    override fun loadNextPage() {
        commandManager.postCommand(
            LoadNextWithPageNumberCommand(
                { executeLoadNextPage(it) },
                { UIProgressErrorItem.Progress },
                { UIProgressErrorItem.Error(it.toString()) { loadNextPage() } }
            )
        )
    }

    private suspend fun executeLoadNextPage(pageNumber: Int): PageDataWithNextPageNumber<UIMainItem> {
        val items =
            withContext(Dispatchers.IO) {
                HardCodeRepository.loadNextMainPage(pageNumber, PAGE_SIZE)
            }
        return PageDataWithNextPageNumber(
            withContext(Dispatchers.Default) { items.map { it.toUIMainItem() } },
            if (items.isEmpty()) null else pageNumber + 1
        )
    }

    override fun removeFromFavorite(item: UIMainItem) {
        if (item.favoriteState.favorite) {
            executeFavoriteChangeAction(item.uid, false)
        }
    }

    override fun addToFavorite(item: UIMainItem) {
        if (!item.favoriteState.favorite) {
            executeFavoriteChangeAction(item.uid, true)
        }
    }

    private fun executeFavoriteChangeAction(uid: String, newFavoriteStatus: Boolean) {
        commandManager.postCommand(
            ChangeFavoriteStatusCommand(
                uid,
                newFavoriteStatus,
                {
                    withContext(Dispatchers.IO) {
                        HardCodeRepository.changeFavoriteStatus(uid, newFavoriteStatus)
                    }
                },
                { Toast.makeText(getApplication(), it.toString(), Toast.LENGTH_SHORT).show() }
            )
        )
    }
}