[Jetcaster] Refactor: create domain models (#1289)

Added the following domain layer objects and corresponding test cases:
* `GetLatestFollowedEpisodesUseCase`
* `PodcastCategoryFilterUseCase`
* `FilterableCategoriesUseCase`

This also required creating interfaces for repository objects to enable
creating fakes for testing. Introducing these changes improves
readability/maintainability of `HomeViewModel` and encourages splitting
up responsibilities to smaller easily testable contained [domain]
objects.

Author: arriolac

Jetcaster/app/src/main/java/com/example/jetcaster/ui/home/Home.kt

@@ -76,9 +76,9 @@ import com.example.jetcaster.R
 import com.example.jetcaster.core.data.database.model.Category
 import com.example.jetcaster.core.data.database.model.EpisodeToPodcast
 import com.example.jetcaster.core.data.database.model.PodcastWithExtraInfo
+import com.example.jetcaster.core.data.model.FilterableCategoriesModel
+import com.example.jetcaster.core.data.model.PodcastCategoryFilterResult
 import com.example.jetcaster.designsystem.theme.Keyline1
-import com.example.jetcaster.ui.home.category.PodcastCategoryViewState
-import com.example.jetcaster.ui.home.discover.DiscoverViewState
 import com.example.jetcaster.ui.home.discover.discoverItems
 import com.example.jetcaster.ui.home.library.libraryItems
 import com.example.jetcaster.ui.theme.JetcasterTheme
@@ -102,8 +102,8 @@ fun Home(
             isRefreshing = viewState.refreshing,
             homeCategories = viewState.homeCategories,
             selectedHomeCategory = viewState.selectedHomeCategory,
-            discoverViewState = viewState.discoverViewState,
-            podcastCategoryViewState = viewState.podcastCategoryViewState,
+            filterableCategoriesModel = viewState.filterableCategoriesModel,
+            podcastCategoryFilterResult = viewState.podcastCategoryFilterResult,
             libraryEpisodes = viewState.libraryEpisodes,
             onHomeCategorySelected = viewModel::onHomeCategorySelected,
             onCategorySelected = viewModel::onCategorySelected,
@@ -159,15 +159,14 @@ fun HomeAppBar(
     )
 }
 
-@OptIn(ExperimentalFoundationApi::class)
 @Composable
 fun Home(
     featuredPodcasts: PersistentList<PodcastWithExtraInfo>,
     isRefreshing: Boolean,
     selectedHomeCategory: HomeCategory,
     homeCategories: List<HomeCategory>,
-    discoverViewState: DiscoverViewState,
-    podcastCategoryViewState: PodcastCategoryViewState,
+    filterableCategoriesModel: FilterableCategoriesModel,
+    podcastCategoryFilterResult: PodcastCategoryFilterResult,
     libraryEpisodes: List<EpisodeToPodcast>,
     modifier: Modifier = Modifier,
     onPodcastUnfollowed: (String) -> Unit,
@@ -214,8 +213,8 @@ fun Home(
             isRefreshing = isRefreshing,
             selectedHomeCategory = selectedHomeCategory,
             homeCategories = homeCategories,
-            discoverViewState = discoverViewState,
-            podcastCategoryViewState = podcastCategoryViewState,
+            filterableCategoriesModel = filterableCategoriesModel,
+            podcastCategoryFilterResult = podcastCategoryFilterResult,
             libraryEpisodes = libraryEpisodes,
             scrimColor = scrimColor,
             onPodcastUnfollowed = onPodcastUnfollowed,
@@ -234,8 +233,8 @@ private fun HomeContent(
     isRefreshing: Boolean,
     selectedHomeCategory: HomeCategory,
     homeCategories: List<HomeCategory>,
-    discoverViewState: DiscoverViewState,
-    podcastCategoryViewState: PodcastCategoryViewState,
+    filterableCategoriesModel: FilterableCategoriesModel,
+    podcastCategoryFilterResult: PodcastCategoryFilterResult,
     libraryEpisodes: List<EpisodeToPodcast>,
     scrimColor: Color,
     modifier: Modifier = Modifier,
@@ -286,8 +285,8 @@ private fun HomeContent(
 
             HomeCategory.Discover -> {
                 discoverItems(
-                    discoverViewState = discoverViewState,
-                    podcastCategoryViewState = podcastCategoryViewState,
+                    filterableCategoriesModel = filterableCategoriesModel,
+                    podcastCategoryFilterResult = podcastCategoryFilterResult,
                     navigateToPlayer = navigateToPlayer,
                     onCategorySelected = onCategorySelected,
                     onTogglePodcastFollowed = onTogglePodcastFollowed
@@ -472,11 +471,11 @@ fun PreviewHomeContent() {
             isRefreshing = false,
             homeCategories = HomeCategory.entries,
             selectedHomeCategory = HomeCategory.Discover,
-            discoverViewState = DiscoverViewState(
+            filterableCategoriesModel = FilterableCategoriesModel(
                 categories = PreviewCategories,
-                selectedCategory = PreviewCategories.first(),
+                selectedCategory = PreviewCategories.firstOrNull()
             ),
-            podcastCategoryViewState = PodcastCategoryViewState(
+            podcastCategoryFilterResult = PodcastCategoryFilterResult(
                 topPodcasts = PreviewPodcastsWithExtraInfo,
                 episodes = PreviewEpisodeToPodcasts,
             ),

Jetcaster/app/src/main/java/com/example/jetcaster/ui/home/HomeViewModel.kt

@@ -22,12 +22,13 @@ import com.example.jetcaster.core.data.database.model.Category
 import com.example.jetcaster.core.data.database.model.EpisodeToPodcast
 import com.example.jetcaster.core.data.database.model.PodcastWithExtraInfo
 import com.example.jetcaster.core.data.di.Graph
-import com.example.jetcaster.core.data.repository.CategoryStore
-import com.example.jetcaster.core.data.repository.EpisodeStore
+import com.example.jetcaster.core.data.domain.FilterableCategoriesUseCase
+import com.example.jetcaster.core.data.domain.GetLatestFollowedEpisodesUseCase
+import com.example.jetcaster.core.data.domain.PodcastCategoryFilterUseCase
+import com.example.jetcaster.core.data.model.FilterableCategoriesModel
+import com.example.jetcaster.core.data.model.PodcastCategoryFilterResult
 import com.example.jetcaster.core.data.repository.PodcastStore
 import com.example.jetcaster.core.data.repository.PodcastsRepository
-import com.example.jetcaster.ui.home.category.PodcastCategoryViewState
-import com.example.jetcaster.ui.home.discover.DiscoverViewState
 import com.example.jetcaster.util.combine
 import kotlinx.collections.immutable.PersistentList
 import kotlinx.collections.immutable.persistentListOf
@@ -36,17 +37,19 @@ import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.catch
-import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
-import kotlinx.coroutines.flow.flowOf
-import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.launch
 
+@OptIn(ExperimentalCoroutinesApi::class)
 class HomeViewModel(
     private val podcastsRepository: PodcastsRepository = Graph.podcastRepository,
-    private val categoryStore: CategoryStore = Graph.categoryStore,
     private val podcastStore: PodcastStore = Graph.podcastStore,
-    private val episodeStore: EpisodeStore = Graph.episodeStore
+    private val getLatestFollowedEpisodesUseCase: GetLatestFollowedEpisodesUseCase =
+        Graph.getLatestFollowedEpisodesUseCase,
+    private val podcastCategoryFilterUseCase: PodcastCategoryFilterUseCase =
+        Graph.podcastCategoryFilterUseCase,
+    private val filterableCategoriesUseCase: FilterableCategoriesUseCase =
+        Graph.filterableCategoriesUseCase
 ) : ViewModel() {
     // Holds our currently selected home category
     private val selectedHomeCategory = MutableStateFlow(HomeCategory.Discover)
@@ -59,64 +62,6 @@ class HomeViewModel(
     // Holds the view state if the UI is refreshing for new data
     private val refreshing = MutableStateFlow(false)
 
-    @OptIn(ExperimentalCoroutinesApi::class)
-    private val libraryEpisodes =
-        podcastStore.followedPodcastsSortedByLastEpisode()
-            .flatMapLatest { followedPodcasts ->
-                if (followedPodcasts.isEmpty()) {
-                    flowOf(emptyList())
-                } else {
-                    combine(
-                        followedPodcasts.map { p ->
-                            episodeStore.episodesInPodcast(p.podcast.uri, 5)
-                        }
-                    ) { allEpisodes ->
-                        allEpisodes.toList().flatten().sortedByDescending { it.episode.published }
-                    }
-                }
-            }
-
-    private val discover = combine(
-        categoryStore.categoriesSortedByPodcastCount()
-            .onEach { categories ->
-                // If we haven't got a selected category yet, select the first
-                if (categories.isNotEmpty() && _selectedCategory.value == null) {
-                    _selectedCategory.value = categories[0]
-                }
-            },
-        _selectedCategory
-    ) { categories, selectedCategory ->
-        DiscoverViewState(
-            categories = categories,
-            selectedCategory = selectedCategory
-        )
-    }
-
-    @OptIn(ExperimentalCoroutinesApi::class)
-    private val podcastCategory = _selectedCategory.flatMapLatest { category ->
-        if (category == null) {
-            return@flatMapLatest flowOf(PodcastCategoryViewState())
-        }
-
-        val recentPodcastsFlow = categoryStore.podcastsInCategorySortedByPodcastCount(
-            category.id,
-            limit = 10
-        )
-
-        val episodesFlow = categoryStore.episodesFromPodcastsInCategory(
-            category.id,
-            limit = 20
-        )
-
-        // Combine our flows and collect them into the view state StateFlow
-        combine(recentPodcastsFlow, episodesFlow) { topPodcasts, episodes ->
-            PodcastCategoryViewState(
-                topPodcasts = topPodcasts,
-                episodes = episodes
-            )
-        }
-    }
-
     val state: StateFlow<HomeViewState>
         get() = _state
 
@@ -129,23 +74,30 @@ class HomeViewModel(
                 selectedHomeCategory,
                 podcastStore.followedPodcastsSortedByLastEpisode(limit = 20),
                 refreshing,
-                discover,
-                podcastCategory,
-                libraryEpisodes
+                _selectedCategory.flatMapLatest { selectedCategory ->
+                    filterableCategoriesUseCase(selectedCategory)
+                },
+                _selectedCategory.flatMapLatest {
+                    podcastCategoryFilterUseCase(it)
+                },
+                getLatestFollowedEpisodesUseCase()
             ) { homeCategories,
                 selectedHomeCategory,
                 podcasts,
                 refreshing,
-                discoverViewState,
-                podcastCategoryViewState,
+                filterableCategories,
+                podcastCategoryFilterResult,
                 libraryEpisodes ->
+
+                _selectedCategory.value = filterableCategories.selectedCategory
+
                 HomeViewState(
                     homeCategories = homeCategories,
                     selectedHomeCategory = selectedHomeCategory,
                     featuredPodcasts = podcasts.toPersistentList(),
                     refreshing = refreshing,
-                    discoverViewState = discoverViewState,
-                    podcastCategoryViewState = podcastCategoryViewState,
+                    filterableCategoriesModel = filterableCategories,
+                    podcastCategoryFilterResult = podcastCategoryFilterResult,
                     libraryEpisodes = libraryEpisodes,
                     errorMessage = null, /* TODO */
                 )
@@ -202,8 +154,8 @@ data class HomeViewState(
     val refreshing: Boolean = false,
     val selectedHomeCategory: HomeCategory = HomeCategory.Discover,
     val homeCategories: List<HomeCategory> = emptyList(),
-    val discoverViewState: DiscoverViewState = DiscoverViewState(),
-    val podcastCategoryViewState: PodcastCategoryViewState = PodcastCategoryViewState(),
+    val filterableCategoriesModel: FilterableCategoriesModel = FilterableCategoriesModel(),
+    val podcastCategoryFilterResult: PodcastCategoryFilterResult = PodcastCategoryFilterResult(),
     val libraryEpisodes: List<EpisodeToPodcast> = emptyList(),
     val errorMessage: String? = null
 )

Jetcaster/app/src/main/java/com/example/jetcaster/ui/home/category/PodcastCategory.kt

@@ -76,11 +76,6 @@ import com.example.jetcaster.util.ToggleFollowPodcastIconButton
 import java.time.format.DateTimeFormatter
 import java.time.format.FormatStyle
 
-data class PodcastCategoryViewState(
-    val topPodcasts: List<PodcastWithExtraInfo> = emptyList(),
-    val episodes: List<EpisodeToPodcast> = emptyList()
-)
-
 fun LazyListScope.podcastCategory(
     topPodcasts: List<PodcastWithExtraInfo>,
     episodes: List<EpisodeToPodcast>,

Jetcaster/app/src/main/java/com/example/jetcaster/ui/home/discover/Discover.kt

@@ -38,23 +38,19 @@ import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
 import com.example.jetcaster.R
 import com.example.jetcaster.core.data.database.model.Category
+import com.example.jetcaster.core.data.model.FilterableCategoriesModel
+import com.example.jetcaster.core.data.model.PodcastCategoryFilterResult
 import com.example.jetcaster.designsystem.theme.Keyline1
-import com.example.jetcaster.ui.home.category.PodcastCategoryViewState
 import com.example.jetcaster.ui.home.category.podcastCategory
 
-data class DiscoverViewState(
-    val categories: List<Category> = emptyList(),
-    val selectedCategory: Category? = null
-)
-
 fun LazyListScope.discoverItems(
-    discoverViewState: DiscoverViewState,
-    podcastCategoryViewState: PodcastCategoryViewState,
+    filterableCategoriesModel: FilterableCategoriesModel,
+    podcastCategoryFilterResult: PodcastCategoryFilterResult,
     navigateToPlayer: (String) -> Unit,
     onCategorySelected: (Category) -> Unit,
     onTogglePodcastFollowed: (String) -> Unit,
 ) {
-    if (discoverViewState.categories.isEmpty() || discoverViewState.selectedCategory == null) {
+    if (filterableCategoriesModel.isEmpty) {
         // TODO: empty state
         return
     }
@@ -63,8 +59,7 @@ fun LazyListScope.discoverItems(
         Spacer(Modifier.height(8.dp))
 
         PodcastCategoryTabs(
-            categories = discoverViewState.categories,
-            selectedCategory = discoverViewState.selectedCategory,
+            filterableCategoriesModel = filterableCategoriesModel,
             onCategorySelected = onCategorySelected,
             modifier = Modifier.fillMaxWidth()
         )
@@ -73,8 +68,8 @@ fun LazyListScope.discoverItems(
     }
 
     podcastCategory(
-        topPodcasts = podcastCategoryViewState.topPodcasts,
-        episodes = podcastCategoryViewState.episodes,
+        topPodcasts = podcastCategoryFilterResult.topPodcasts,
+        episodes = podcastCategoryFilterResult.episodes,
         navigateToPlayer = navigateToPlayer,
         onTogglePodcastFollowed = onTogglePodcastFollowed
     )
@@ -84,20 +79,21 @@ private val emptyTabIndicator: @Composable (List<TabPosition>) -> Unit = {}
 
 @Composable
 private fun PodcastCategoryTabs(
-    categories: List<Category>,
-    selectedCategory: Category,
+    filterableCategoriesModel: FilterableCategoriesModel,
     onCategorySelected: (Category) -> Unit,
     modifier: Modifier = Modifier
 ) {
-    val selectedIndex = categories.indexOfFirst { it == selectedCategory }
+    val selectedIndex = filterableCategoriesModel.categories.indexOf(
+        filterableCategoriesModel.selectedCategory
+    )
     ScrollableTabRow(
         selectedTabIndex = selectedIndex,
         divider = {}, /* Disable the built-in divider */
         edgePadding = Keyline1,
         indicator = emptyTabIndicator,
         modifier = modifier
     ) {
-        categories.forEachIndexed { index, category ->
+        filterableCategoriesModel.categories.forEachIndexed { index, category ->
             Tab(
                 selected = index == selectedIndex,
                 onClick = { onCategorySelected(category) }

Jetcaster/core/build.gradle.kts

@@ -54,4 +54,8 @@ dependencies {
   implementation(libs.rometools.modules)
 
   coreLibraryDesugaring(libs.core.jdk.desugaring)
+
+  // Testing
+  testImplementation(libs.junit)
+  testImplementation(libs.kotlinx.coroutines.test)
 }

Jetcaster/core/src/main/java/com/example/jetcaster/core/data/database/dao/EpisodesDao.kt

@@ -65,4 +65,16 @@ abstract class EpisodesDao : BaseDao<Episode> {
 
     @Query("SELECT COUNT(*) FROM episodes")
     abstract suspend fun count(): Int
+
+    @Query(
+        """
+        SELECT * FROM episodes WHERE podcast_uri IN (:podcastUris)
+        ORDER BY datetime(published) DESC
+        LIMIT :limit
+        """
+    )
+    abstract fun episodesForPodcasts(
+        podcastUris: List<String>,
+        limit: Int
+    ): Flow<List<EpisodeToPodcast>>
 }