Mark all news resources read on first sync

Otherwise, there will be unread articles until the user clicks through
every article that has ever been published.

core/data/src/main/java/com/google/samples/apps/nowinandroid/core/data/repository/OfflineFirstNewsRepository.kt

@@ -63,10 +63,12 @@ class OfflineFirstNewsRepository @Inject constructor(
     )
         .map { it.map(PopulatedNewsResource::asExternalModel) }
 
-    override suspend fun syncWith(synchronizer: Synchronizer) =
+    override suspend fun syncWith(synchronizer: Synchronizer): Boolean {
-        synchronizer.changeListSync(
+        var isFirstSync = false
+        return synchronizer.changeListSync(
             versionReader = ChangeListVersions::newsResourceVersion,
             changeListFetcher = { currentVersion ->
+                isFirstSync = currentVersion <= 0
                 network.getNewsResourceChangeList(after = currentVersion)
             },
             versionUpdater = { latestVersion ->
@@ -94,6 +96,12 @@ class OfflineFirstNewsRepository @Inject constructor(
                     else -> emptySet()
                 }
 
+                if (isFirstSync) {
+                    // When we first retrieve news, mark everything viewed, so that we aren't
+                    // overwhelmed with all historical news.
+                    niaPreferencesDataSource.setNewsResourcesViewed(changedIds, true)
+                }
+
                 // Obtain the news resources which have changed from the network and upsert them locally
                 changedIds.chunked(SYNC_BATCH_SIZE).forEach { chunkedIds ->
                     val networkNewsResources = network.getNewsResources(ids = chunkedIds)
@@ -138,3 +146,4 @@ class OfflineFirstNewsRepository @Inject constructor(
             },
         )
     }
+}

core/data/src/test/java/com/google/samples/apps/nowinandroid/core/data/repository/OfflineFirstNewsRepositoryTest.kt

@@ -288,6 +288,33 @@ class OfflineFirstNewsRepositoryTest {
             )
         }
 
+    @Test
+    fun offlineFirstNewsRepository_sync_marks_as_read_on_first_run() =
+        testScope.runTest {
+            subject.syncWith(synchronizer)
+
+            assertEquals(
+                network.getNewsResources().map { it.id }.toSet(),
+                niaPreferencesDataSource.userData.first().viewedNewsResources,
+            )
+        }
+
+    @Test
+    fun offlineFirstNewsRepository_sync_does_not_mark_as_read_on_subsequent_run() =
+        testScope.runTest {
+            // Pretend that we already have up to change list 7
+            synchronizer.updateChangeListVersions {
+                copy(newsResourceVersion = 7)
+            }
+
+            subject.syncWith(synchronizer)
+
+            assertEquals(
+                emptySet(),
+                niaPreferencesDataSource.userData.first().viewedNewsResources,
+            )
+        }
+
     @Test
     fun offlineFirstNewsRepository_sends_notifications_for_newly_synced_news_that_is_followed() =
         testScope.runTest {

core/datastore/src/main/java/com/google/samples/apps/nowinandroid/core/datastore/NiaPreferencesDataSource.kt

@@ -139,12 +139,18 @@ class NiaPreferencesDataSource @Inject constructor(
     }
 
     suspend fun setNewsResourceViewed(newsResourceId: String, viewed: Boolean) {
+        setNewsResourcesViewed(listOf(newsResourceId), viewed)
+    }
+
+    suspend fun setNewsResourcesViewed(newsResourceIds: List<String>, viewed: Boolean) {
         userPreferences.updateData {
             it.copy {
+                newsResourceIds.forEach {
                     if (viewed) {
-                    viewedNewsResourceIds.put(newsResourceId, true)
+                        viewedNewsResourceIds.put(it, true)
                     } else {
-                    viewedNewsResourceIds.remove(newsResourceId)
+                        viewedNewsResourceIds.remove(it)
+                    }
                 }
             }
         }