ErrorMonitor implementation more like NetworkMonitor

Removed all but the message.stateIn from AppState

Added interface and implementation, dependency injection

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivity.kt

@@ -41,6 +41,7 @@ import com.google.samples.apps.nowinandroid.MainActivityUiState.Success
 import com.google.samples.apps.nowinandroid.core.analytics.AnalyticsHelper
 import com.google.samples.apps.nowinandroid.core.analytics.LocalAnalyticsHelper
 import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourceRepository
+import com.google.samples.apps.nowinandroid.core.data.util.ErrorMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.NetworkMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.TimeZoneMonitor
 import com.google.samples.apps.nowinandroid.core.designsystem.theme.NiaTheme
@@ -69,6 +70,9 @@ class MainActivity : ComponentActivity() {
     @Inject
     lateinit var networkMonitor: NetworkMonitor
 
+    @Inject
+    lateinit var errorMonitor: ErrorMonitor
+
     @Inject
     lateinit var timeZoneMonitor: TimeZoneMonitor
 
@@ -133,6 +137,7 @@ class MainActivity : ComponentActivity() {
 
             val appState = rememberNiaAppState(
                 networkMonitor = networkMonitor,
+                errorMonitor = errorMonitor,
                 userNewsResourceRepository = userNewsResourceRepository,
                 timeZoneMonitor = timeZoneMonitor,
             )

app/src/main/kotlin/com/google/samples/apps/nowinandroid/ui/NiaAppState.kt

@@ -29,6 +29,7 @@ import androidx.navigation.compose.rememberNavController
 import androidx.navigation.navOptions
 import androidx.tracing.trace
 import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourceRepository
+import com.google.samples.apps.nowinandroid.core.data.util.ErrorMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.NetworkMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.TimeZoneMonitor
 import com.google.samples.apps.nowinandroid.core.ui.TrackDisposableJank
@@ -44,19 +45,17 @@ import com.google.samples.apps.nowinandroid.navigation.TopLevelDestination.BOOKM
 import com.google.samples.apps.nowinandroid.navigation.TopLevelDestination.FOR_YOU
 import com.google.samples.apps.nowinandroid.navigation.TopLevelDestination.INTERESTS
 import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
-import kotlinx.coroutines.flow.update
 import kotlinx.datetime.TimeZone
-import java.util.UUID
 
 @Composable
 fun rememberNiaAppState(
     networkMonitor: NetworkMonitor,
+    errorMonitor: ErrorMonitor,
     userNewsResourceRepository: UserNewsResourceRepository,
     timeZoneMonitor: TimeZoneMonitor,
     coroutineScope: CoroutineScope = rememberCoroutineScope(),
@@ -67,6 +66,7 @@ fun rememberNiaAppState(
         navController,
         coroutineScope,
         networkMonitor,
+        errorMonitor,
         userNewsResourceRepository,
         timeZoneMonitor,
     ) {
@@ -74,6 +74,7 @@ fun rememberNiaAppState(
             navController = navController,
             coroutineScope = coroutineScope,
             networkMonitor = networkMonitor,
+            errorMonitor = errorMonitor,
             userNewsResourceRepository = userNewsResourceRepository,
             timeZoneMonitor = timeZoneMonitor,
         )
@@ -85,6 +86,7 @@ class NiaAppState(
     val navController: NavHostController,
     coroutineScope: CoroutineScope,
     networkMonitor: NetworkMonitor,
+    errorMonitor: ErrorMonitor,
     userNewsResourceRepository: UserNewsResourceRepository,
     timeZoneMonitor: TimeZoneMonitor,
 ) {
@@ -108,44 +110,12 @@ class NiaAppState(
             initialValue = false,
         )
 
-    /**
+    val errorMessage = errorMonitor.errorMessage.stateIn(
-     * List of [ErrorMessage] to be shown to the user, via Snackbar.
-     */
-    private val errorMessages = MutableStateFlow<List<ErrorMessage>>(emptyList())
-
-    /**
-     * Current [ErrorMessage] or null if there isn't any.
-     */
-    val errorMessage: StateFlow<ErrorMessage?> = errorMessages.map { it.firstOrNull() }.stateIn(
         scope = coroutineScope,
         started = SharingStarted.WhileSubscribed(5_000),
         initialValue = null,
     )
 
-    /**
-     * Creates an [ErrorMessage] from String value and adds it to the list.
-     *
-     * @param error: String value of the error message.
-     *
-     * Returns the ID of the new [ErrorMessage] if success
-     * Returns null if [error] is Blank
-     */
-    fun addErrorMessage(error: String): String? {
-        if (error.isNotBlank()) {
-            val newError = ErrorMessage(error)
-            errorMessages.update { it + newError }
-            return newError.id
-        }
-        return null
-    }
-
-    /**
-     * Removes the [ErrorMessage] with the specified [id] from the list.
-     */
-    fun clearErrorMessage(id: String) {
-        errorMessages.update { it.filter { item -> item.id != id } }
-    }
-
     /**
      * Map of top level destinations to be used in the TopBar, BottomBar and NavRail. The key is the
      * route.
@@ -227,11 +197,3 @@ private fun NavigationTrackingSideEffect(navController: NavHostController) {
         }
     }
 }
-
-/**
- * Models the data needed for an error message to be displayed and tracked.
- */
-data class ErrorMessage(
-    val message: String,
-    val id: String = UUID.randomUUID().toString(),
-)

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/di/DataModule.kt

@@ -27,7 +27,9 @@ import com.google.samples.apps.nowinandroid.core.data.repository.SearchContentsR
 import com.google.samples.apps.nowinandroid.core.data.repository.TopicsRepository
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
 import com.google.samples.apps.nowinandroid.core.data.util.ConnectivityManagerNetworkMonitor
+import com.google.samples.apps.nowinandroid.core.data.util.ErrorMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.NetworkMonitor
+import com.google.samples.apps.nowinandroid.core.data.util.SnackbarErrorMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.TimeZoneBroadcastMonitor
 import com.google.samples.apps.nowinandroid.core.data.util.TimeZoneMonitor
 import dagger.Binds
@@ -71,4 +73,9 @@ abstract class DataModule {
 
     @Binds
     internal abstract fun binds(impl: TimeZoneBroadcastMonitor): TimeZoneMonitor
+
+    @Binds
+    internal abstract fun bindsErrorMonitor(
+        errorMonitor: SnackbarErrorMonitor,
+    ): ErrorMonitor
 }

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/util/ErrorMonitor.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.core.data.util
+
+import kotlinx.coroutines.flow.Flow
+
+/**
+ * Interface for handling error messages.
+ */
+interface ErrorMonitor {
+    fun addErrorMessage(error: String): String?
+    fun clearErrorMessage(id: String)
+    val errorMessage: Flow<ErrorMessage?>
+}

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/util/SnackbarErrorMonitor.kt

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.core.data.util
+
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.update
+import java.util.UUID
+
+/**
+ * Interface implementation for handling general errors.
+ */
+
+class SnackbarErrorMonitor : ErrorMonitor {
+    /**
+     * List of [ErrorMessage] to be shown to the user, via Snackbar.
+     */
+    private val errorMessages = MutableStateFlow<List<ErrorMessage>>(emptyList())
+
+    /**
+     * Current [ErrorMessage] or null if there are none.
+     */
+    override val errorMessage: Flow<ErrorMessage?> = errorMessages.map { it.firstOrNull() }
+
+    /**
+     * Creates an [ErrorMessage] from String value and adds it to the list.
+     *
+     * @param error: String value of the error message.
+     *
+     * Returns the ID of the new [ErrorMessage] if success
+     * Returns null if [error] is Blank
+     */
+    override fun addErrorMessage(error: String): String? {
+        if (error.isNotBlank()) {
+            val newError = ErrorMessage(error)
+            errorMessages.update { it + newError }
+            return newError.id
+        }
+        return null
+    }
+
+    /**
+     * Removes the [ErrorMessage] with the specified [id] from the list.
+     */
+    override fun clearErrorMessage(id: String) {
+        errorMessages.update { it.filter { item -> item.id != id } }
+    }
+}
+
+/**
+ * Models the data needed for an error message to be displayed and tracked.
+ */
+data class ErrorMessage(
+    val message: String,
+    val id: String = UUID.randomUUID().toString(),
+)