Add UseCase for getting followed news resources, refactor ForYouVM

core/domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/GetUserNewsResourcesUseCase.kt

@@ -24,7 +24,11 @@ import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
 import com.google.samples.apps.nowinandroid.core.model.data.UserData
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.filterNot
+import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.map
 import javax.inject.Inject
 
 /**
@@ -51,6 +55,43 @@ class GetUserNewsResourcesUseCase @Inject constructor(
         }.mapToUserNewsResources(userDataRepository.userData)
 }
 
+class GetFollowedUserNewsResourcesUseCase @Inject constructor(
+    private val userDataRepository: UserDataRepository,
+    val getUserNewsResources: GetUserNewsResourcesUseCase,
+) {
+    /**
+     * Returns a list of UserNewsResources which the user is following
+     */
+    operator fun invoke(): Flow<List<UserNewsResource>> =
+        userDataRepository.userData.map { userData ->
+            if (shouldShowEmptyFeed(userData)) {
+                null
+            } else {
+                userData.followedTopics
+            }
+        }
+            .distinctUntilChanged()
+            .flatMapLatest { followedTopics ->
+                if (followedTopics == null) {
+                    flowOf(emptyList())
+                } else {
+                    getUserNewsResources(filterTopicIds = followedTopics)
+                }
+            }
+
+    /**
+     * If the user hasn't completed the onboarding and hasn't selected any interests
+     * show an empty news list to clearly demonstrate that their selections affect the
+     * news articles they will see.
+     *
+     * Note: It should not be possible for the user to get into a state where the onboarding
+     * is not displayed AND they haven't followed any topics, however, this method is to safeguard
+     * against that scenario in future.
+     */
+    private fun shouldShowEmptyFeed(userData: UserData) =
+        !userData.shouldHideOnboarding && userData.followedTopics.isEmpty()
+}
+
 private fun Flow<List<NewsResource>>.mapToUserNewsResources(
     userDataStream: Flow<UserData>,
 ): Flow<List<UserNewsResource>> =

feature/foryou/src/main/java/com/google/samples/apps/nowinandroid/feature/foryou/ForYouViewModel.kt

@@ -21,7 +21,7 @@ import androidx.lifecycle.viewModelScope
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
 import com.google.samples.apps.nowinandroid.core.data.util.SyncStatusMonitor
 import com.google.samples.apps.nowinandroid.core.domain.GetFollowableTopicsUseCase
-import com.google.samples.apps.nowinandroid.core.domain.GetUserNewsResourcesUseCase
+import com.google.samples.apps.nowinandroid.core.domain.GetFollowedUserNewsResourcesUseCase
 import com.google.samples.apps.nowinandroid.core.domain.model.UserNewsResource
 import com.google.samples.apps.nowinandroid.core.ui.NewsFeedUiState
 import dagger.hilt.android.lifecycle.HiltViewModel
@@ -29,8 +29,6 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
-import kotlinx.coroutines.flow.flatMapLatest
-import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
@@ -40,7 +38,7 @@ import javax.inject.Inject
 class ForYouViewModel @Inject constructor(
     syncStatusMonitor: SyncStatusMonitor,
     private val userDataRepository: UserDataRepository,
-    private val getSaveableNewsResources: GetUserNewsResourcesUseCase,
+    getFollowedUserNewsResources: GetFollowedUserNewsResourcesUseCase,
     getFollowableTopics: GetFollowableTopicsUseCase,
 ) : ViewModel() {
 
@@ -55,26 +53,9 @@ class ForYouViewModel @Inject constructor(
         )
 
     val feedState: StateFlow<NewsFeedUiState> =
-        userDataRepository.userData
-            .map { userData ->
-                // If the user hasn't completed the onboarding and hasn't selected any interests
-                // show an empty news list to clearly demonstrate that their selections affect the
-                // news articles they will see.
-                if (!userData.shouldHideOnboarding &&
-                    userData.followedTopics.isEmpty()
-                ) {
-                    flowOf(NewsFeedUiState.Success(emptyList()))
-                } else {
-                    getSaveableNewsResources(
-                        filterTopicIds = userData.followedTopics,
-                    )
-                        .map<List<UserNewsResource>, NewsFeedUiState>(NewsFeedUiState::Success)
-                }
-            }
-            // Flatten the feed flows.
-            // As the selected topics and topic state changes, this will cancel the old feed
-            // monitoring and start the new one.
-            .flatMapLatest { it }
+        getFollowedUserNewsResources().map {
+            NewsFeedUiState.Success(it)
+        }
             .stateIn(
                 scope = viewModelScope,
                 started = SharingStarted.WhileSubscribed(5_000),

feature/foryou/src/test/java/com/google/samples/apps/nowinandroid/feature/foryou/ForYouViewModelTest.kt

@@ -17,6 +17,7 @@
 package com.google.samples.apps.nowinandroid.feature.foryou
 
 import com.google.samples.apps.nowinandroid.core.domain.GetFollowableTopicsUseCase
+import com.google.samples.apps.nowinandroid.core.domain.GetFollowedUserNewsResourcesUseCase
 import com.google.samples.apps.nowinandroid.core.domain.GetUserNewsResourcesUseCase
 import com.google.samples.apps.nowinandroid.core.domain.model.FollowableTopic
 import com.google.samples.apps.nowinandroid.core.domain.model.UserNewsResource
@@ -60,6 +61,11 @@ class ForYouViewModelTest {
         newsRepository = newsRepository,
         userDataRepository = userDataRepository,
     )
+    private val getFollowedUserNewsResourcesUseCase = GetFollowedUserNewsResourcesUseCase(
+        userDataRepository = userDataRepository,
+        getUserNewsResources = getUserNewsResourcesUseCase,
+    )
+
     private val getFollowableTopicsUseCase = GetFollowableTopicsUseCase(
         topicsRepository = topicsRepository,
         userDataRepository = userDataRepository,
@@ -71,7 +77,7 @@ class ForYouViewModelTest {
         viewModel = ForYouViewModel(
             syncStatusMonitor = syncStatusMonitor,
             userDataRepository = userDataRepository,
-            getSaveableNewsResources = getUserNewsResourcesUseCase,
+            getFollowedUserNewsResources = getFollowedUserNewsResourcesUseCase,
             getFollowableTopics = getFollowableTopicsUseCase,
         )
     }