Handle items deleted on server during sync

Change-Id: Ifa2250d9ce4b3dedf10804554a39fb4d62ffed9d

core-database/src/androidTest/java/com/google/samples/apps/nowinandroid/core/database/dao/NewsResourceDaoTest.kt

@@ -305,6 +305,49 @@ class NewsResourceDaoTest {
                 filteredNewsResources.map { it.entity.id }
             )
         }
+
+    @Test
+    fun newsResourceDao_deletes_items_by_ids() =
+        runTest {
+            val newsResourceEntities = listOf(
+                testNewsResource(
+                    id = 0,
+                    millisSinceEpoch = 0,
+                ),
+                testNewsResource(
+                    id = 1,
+                    millisSinceEpoch = 3,
+                ),
+                testNewsResource(
+                    id = 2,
+                    millisSinceEpoch = 1,
+                ),
+                testNewsResource(
+                    id = 3,
+                    millisSinceEpoch = 2,
+                ),
+            )
+            val episodeEntityShells = newsResourceEntities
+                .map(NewsResourceEntity::episodeEntityShell)
+                .distinct()
+
+            episodeDao.upsertEpisodes(episodeEntityShells)
+            newsResourceDao.upsertNewsResources(newsResourceEntities)
+
+            val (toDelete, toKeep) = newsResourceEntities.partition { it.id % 2 == 0 }
+
+            newsResourceDao.deleteNewsResources(
+                toDelete.map(NewsResourceEntity::id)
+            )
+
+            assertEquals(
+                toKeep.map(NewsResourceEntity::id)
+                    .toSet(),
+                newsResourceDao.getNewsResourcesStream().first()
+                    .map { it.entity.id }
+                    .toSet()
+            )
+        }
 }
 
 private fun testAuthorEntity(

core-database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/AuthorDao.kt

@@ -54,4 +54,15 @@ interface AuthorDao {
         insertMany = ::insertOrIgnoreAuthors,
         updateMany = ::updateAuthors
     )
+
+    /**
+     * Deletes rows in the db matching the specified [ids]
+     */
+    @Query(
+        value = """
+            DELETE FROM authors
+            WHERE id in (:ids)
+        """
+    )
+    suspend fun deleteAuthors(ids: List<Int>)
 }

core-database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/EpisodeDao.kt

@@ -56,4 +56,15 @@ interface EpisodeDao {
         insertMany = ::insertOrIgnoreEpisodes,
         updateMany = ::updateEpisodes
     )
+
+    /**
+     * Deletes rows in the db matching the specified [ids]
+     */
+    @Query(
+        value = """
+            DELETE FROM episodes
+            WHERE id in (:ids)
+        """
+    )
+    suspend fun deleteEpisodes(ids: List<Int>)
 }

core-database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/NewsResourceDao.kt

@@ -94,4 +94,15 @@ interface NewsResourceDao {
     suspend fun insertOrIgnoreAuthorCrossRefEntities(
         newsResourceAuthorCrossReferences: List<NewsResourceAuthorCrossRef>
     )
+
+    /**
+     * Deletes rows in the db matching the specified [ids]
+     */
+    @Query(
+        value = """
+            DELETE FROM news_resources
+            WHERE id in (:ids)
+        """
+    )
+    suspend fun deleteNewsResources(ids: List<Int>)
 }

core-database/src/main/java/com/google/samples/apps/nowinandroid/core/database/dao/TopicDao.kt

@@ -70,4 +70,15 @@ interface TopicDao {
         insertMany = ::insertOrIgnoreTopics,
         updateMany = ::updateTopics
     )
+
+    /**
+     * Deletes rows in the db matching the specified [ids]
+     */
+    @Query(
+        value = """
+            DELETE FROM topics
+            WHERE id in (:ids)
+        """
+    )
+    suspend fun deleteTopics(ids: List<Int>)
 }

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

@@ -18,12 +18,38 @@ package com.google.samples.apps.nowinandroid.core.domain
 
 import android.util.Log
 import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
-import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
 import kotlin.coroutines.cancellation.CancellationException
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
 
+/**
+ * Interface marker for a class that manages synchronization between local data and a remote
+ * source for a [Syncable].
+ */
+interface Synchronizer {
+    suspend fun getChangeListVersions(): ChangeListVersions
+
+    suspend fun updateChangeListVersions(update: ChangeListVersions.() -> ChangeListVersions)
+
+    /**
+     * Syntactic sugar to call [Syncable.syncWith] while omitting the synchronizer argument
+     */
+    suspend fun Syncable.sync() = this@sync.syncWith(this@Synchronizer)
+}
+
+/**
+ * Interface marker for a class that is synchronized with a remote source. Syncing must not be
+ * performed concurrently and it is the [Synchronizer]'s responsibility to ensure this.
+ */
+interface Syncable {
+    /**
+     * Synchronizes the local database in backing the repository with the network.
+     * Returns if the sync was successful or not.
+     */
+    suspend fun syncWith(synchronizer: Synchronizer): Boolean
+}
+
 /**
  * Attempts [block], returning a successful [Result] if it succeeds, otherwise a [Result.Failure]
  * taking care not to break structured concurrency
@@ -46,30 +72,35 @@ private suspend fun <T> suspendRunCatching(block: suspend () -> T): Result<T> =
  * [versionReader] Reads the current version of the model that needs to be synced
  * [changeListFetcher] Fetches the change list for the model
  * [versionUpdater] Updates the [ChangeListVersions] after a successful sync
- * [modelUpdater] Updates the model by consuming the ids of the models that have changed.
+ * [modelDeleter] Deletes models by consuming the ids of the models that have been deleted.
+ * [modelUpdater] Updates models by consuming the ids of the models that have changed.
  *
- * Note that the blocks defined above may be run concurrently due to concurrent calls
+ * Note that the blocks defined above are never run concurrently, and the [Synchronizer]
- * to [changeListSync]. It is the caller's responsibility to make [modelUpdater] performs atomic
+ * implementation must guarantee this.
- * operations.
  */
-suspend fun changeListSync(
+suspend fun Synchronizer.changeListSync(
-    niaPreferences: NiaPreferences,
     versionReader: (ChangeListVersions) -> Int,
     changeListFetcher: suspend (Int) -> List<NetworkChangeList>,
     versionUpdater: ChangeListVersions.(Int) -> ChangeListVersions,
-    modelUpdater: suspend (List<Int>) -> Unit
+    modelDeleter: suspend (List<Int>) -> Unit,
+    modelUpdater: suspend (List<Int>) -> Unit,
 ) = suspendRunCatching {
     // Fetch the change list since last sync (akin to a git fetch)
-    val currentVersion = versionReader(niaPreferences.getChangeListVersions())
+    val currentVersion = versionReader(getChangeListVersions())
     val changeList = changeListFetcher(currentVersion)
     if (changeList.isEmpty()) return@suspendRunCatching true
 
+    val (deleted, updated) = changeList.partition(NetworkChangeList::isDelete)
+
+    // Delete models that have been deleted server-side
+    modelDeleter(deleted.map(NetworkChangeList::id))
+
     // Using the change list, pull down and save the changes (akin to a git pull)
-    modelUpdater(changeList.map(NetworkChangeList::id))
+    modelUpdater(updated.map(NetworkChangeList::id))
 
     // Update the last synced version (akin to updating local git HEAD)
     val latestVersion = changeList.last().changeListVersion
-    niaPreferences.updateChangeListVersion {
+    updateChangeListVersions {
         versionUpdater(latestVersion)
     }
 }.isSuccess

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/AuthorsRepository.kt

@@ -16,10 +16,11 @@
 
 package com.google.samples.apps.nowinandroid.core.domain.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Syncable
 import com.google.samples.apps.nowinandroid.core.model.data.Author
 import kotlinx.coroutines.flow.Flow
 
-interface AuthorsRepository {
+interface AuthorsRepository : Syncable {
     /**
      * Gets the available Authors as a stream
      */
@@ -39,10 +40,4 @@ interface AuthorsRepository {
      * Returns the users currently followed authors
      */
     fun getFollowedAuthorIdsStream(): Flow<Set<Int>>
-
-    /**
-     * Synchronizes the local database in backing the repository with the network.
-     * Returns if the sync was successful or not.
-     */
-    suspend fun sync(): Boolean
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalAuthorsRepository.kt

@@ -21,6 +21,7 @@ import com.google.samples.apps.nowinandroid.core.database.model.AuthorEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.changeListSync
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
 import com.google.samples.apps.nowinandroid.core.model.data.Author
@@ -51,20 +52,21 @@ class LocalAuthorsRepository @Inject constructor(
 
     override fun getFollowedAuthorIdsStream(): Flow<Set<Int>> = niaPreferences.followedAuthorIds
 
-    override suspend fun sync(): Boolean = changeListSync(
+    override suspend fun syncWith(synchronizer: Synchronizer): Boolean =
-        niaPreferences = niaPreferences,
+        synchronizer.changeListSync(
-        versionReader = ChangeListVersions::authorVersion,
+            versionReader = ChangeListVersions::authorVersion,
-        changeListFetcher = { currentVersion ->
+            changeListFetcher = { currentVersion ->
-            network.getAuthorChangeList(after = currentVersion)
+                network.getAuthorChangeList(after = currentVersion)
-        },
+            },
-        versionUpdater = { latestVersion ->
+            versionUpdater = { latestVersion ->
-            copy(authorVersion = latestVersion)
+                copy(authorVersion = latestVersion)
-        },
+            },
-        modelUpdater = { changedIds ->
+            modelDeleter = authorDao::deleteAuthors,
-            val networkAuthors = network.getAuthors(ids = changedIds)
+            modelUpdater = { changedIds ->
-            authorDao.upsertAuthors(
+                val networkAuthors = network.getAuthors(ids = changedIds)
-                entities = networkAuthors.map(NetworkAuthor::asEntity)
+                authorDao.upsertAuthors(
-            )
+                    entities = networkAuthors.map(NetworkAuthor::asEntity)
-        }
+                )
-    )
+            }
+        )
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalNewsRepository.kt

@@ -26,7 +26,7 @@ import com.google.samples.apps.nowinandroid.core.database.model.PopulatedNewsRes
 import com.google.samples.apps.nowinandroid.core.database.model.TopicEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
-import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.changeListSync
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
 import com.google.samples.apps.nowinandroid.core.domain.model.authorCrossReferences
@@ -50,7 +50,6 @@ class LocalNewsRepository @Inject constructor(
     private val authorDao: AuthorDao,
     private val topicDao: TopicDao,
     private val network: NiANetwork,
-    private val niaPreferences: NiaPreferences,
 ) : NewsRepository {
 
     override fun getNewsResourcesStream(): Flow<List<NewsResource>> =
@@ -66,53 +65,54 @@ class LocalNewsRepository @Inject constructor(
     )
         .map { it.map(PopulatedNewsResource::asExternalModel) }
 
-    override suspend fun sync() = changeListSync(
+    override suspend fun syncWith(synchronizer: Synchronizer) =
-        niaPreferences = niaPreferences,
+        synchronizer.changeListSync(
-        versionReader = ChangeListVersions::newsResourceVersion,
+            versionReader = ChangeListVersions::newsResourceVersion,
-        changeListFetcher = { currentVersion ->
+            changeListFetcher = { currentVersion ->
-            network.getNewsResourceChangeList(after = currentVersion)
+                network.getNewsResourceChangeList(after = currentVersion)
-        },
+            },
-        versionUpdater = { latestVersion ->
+            versionUpdater = { latestVersion ->
-            copy(newsResourceVersion = latestVersion)
+                copy(newsResourceVersion = latestVersion)
-        },
+            },
-        modelUpdater = { changedIds ->
+            modelDeleter = newsResourceDao::deleteNewsResources,
-            val networkNewsResources = network.getNewsResources(ids = changedIds)
+            modelUpdater = { changedIds ->
+                val networkNewsResources = network.getNewsResources(ids = changedIds)
 
-            // Order of invocation matters to satisfy id and foreign key constraints!
+                // Order of invocation matters to satisfy id and foreign key constraints!
 
-            topicDao.insertOrIgnoreTopics(
+                topicDao.insertOrIgnoreTopics(
-                topicEntities = networkNewsResources
+                    topicEntities = networkNewsResources
-                    .map(NetworkNewsResource::topicEntityShells)
+                        .map(NetworkNewsResource::topicEntityShells)
-                    .flatten()
+                        .flatten()
-                    .distinctBy(TopicEntity::id)
+                        .distinctBy(TopicEntity::id)
-            )
+                )
-            authorDao.insertOrIgnoreAuthors(
+                authorDao.insertOrIgnoreAuthors(
-                authorEntities = networkNewsResources
+                    authorEntities = networkNewsResources
-                    .map(NetworkNewsResource::authorEntityShells)
+                        .map(NetworkNewsResource::authorEntityShells)
-                    .flatten()
+                        .flatten()
-                    .distinctBy(AuthorEntity::id)
+                        .distinctBy(AuthorEntity::id)
-            )
+                )
-            episodeDao.insertOrIgnoreEpisodes(
+                episodeDao.insertOrIgnoreEpisodes(
-                episodeEntities = networkNewsResources
+                    episodeEntities = networkNewsResources
-                    .map(NetworkNewsResource::episodeEntityShell)
+                        .map(NetworkNewsResource::episodeEntityShell)
-                    .distinctBy(EpisodeEntity::id)
+                        .distinctBy(EpisodeEntity::id)
-            )
+                )
-            newsResourceDao.upsertNewsResources(
+                newsResourceDao.upsertNewsResources(
-                newsResourceEntities = networkNewsResources
+                    newsResourceEntities = networkNewsResources
-                    .map(NetworkNewsResource::asEntity)
+                        .map(NetworkNewsResource::asEntity)
-            )
+                )
-            newsResourceDao.insertOrIgnoreTopicCrossRefEntities(
+                newsResourceDao.insertOrIgnoreTopicCrossRefEntities(
-                newsResourceTopicCrossReferences = networkNewsResources
+                    newsResourceTopicCrossReferences = networkNewsResources
-                    .map(NetworkNewsResource::topicCrossReferences)
+                        .map(NetworkNewsResource::topicCrossReferences)
-                    .distinct()
+                        .distinct()
-                    .flatten()
+                        .flatten()
-            )
+                )
-            newsResourceDao.insertOrIgnoreAuthorCrossRefEntities(
+                newsResourceDao.insertOrIgnoreAuthorCrossRefEntities(
-                newsResourceAuthorCrossReferences = networkNewsResources
+                    newsResourceAuthorCrossReferences = networkNewsResources
-                    .map(NetworkNewsResource::authorCrossReferences)
+                        .map(NetworkNewsResource::authorCrossReferences)
-                    .distinct()
+                        .distinct()
-                    .flatten()
+                        .flatten()
-            )
+                )
-        }
+            }
-    )
+        )
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalTopicsRepository.kt

@@ -21,6 +21,7 @@ import com.google.samples.apps.nowinandroid.core.database.model.TopicEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.changeListSync
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
 import com.google.samples.apps.nowinandroid.core.model.data.Topic
@@ -54,20 +55,21 @@ class LocalTopicsRepository @Inject constructor(
 
     override fun getFollowedTopicIdsStream() = niaPreferences.followedTopicIds
 
-    override suspend fun sync(): Boolean = changeListSync(
+    override suspend fun syncWith(synchronizer: Synchronizer): Boolean =
-        niaPreferences = niaPreferences,
+        synchronizer.changeListSync(
-        versionReader = ChangeListVersions::topicVersion,
+            versionReader = ChangeListVersions::topicVersion,
-        changeListFetcher = { currentVersion ->
+            changeListFetcher = { currentVersion ->
-            network.getTopicChangeList(after = currentVersion)
+                network.getTopicChangeList(after = currentVersion)
-        },
+            },
-        versionUpdater = { latestVersion ->
+            versionUpdater = { latestVersion ->
-            copy(topicVersion = latestVersion)
+                copy(topicVersion = latestVersion)
-        },
+            },
-        modelUpdater = { changedIds ->
+            modelDeleter = topicDao::deleteTopics,
-            val networkTopics = network.getTopics(ids = changedIds)
+            modelUpdater = { changedIds ->
-            topicDao.upsertTopics(
+                val networkTopics = network.getTopics(ids = changedIds)
-                entities = networkTopics.map(NetworkTopic::asEntity)
+                topicDao.upsertTopics(
-            )
+                    entities = networkTopics.map(NetworkTopic::asEntity)
-        }
+                )
-    )
+            }
+        )
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/NewsRepository.kt

@@ -16,13 +16,14 @@
 
 package com.google.samples.apps.nowinandroid.core.domain.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Syncable
 import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
 import kotlinx.coroutines.flow.Flow
 
 /**
  * Data layer implementation for [NewsResource]
  */
-interface NewsRepository {
+interface NewsRepository : Syncable {
     /**
      * Returns available news resources as a stream.
      */
@@ -35,10 +36,4 @@ interface NewsRepository {
         filterAuthorIds: Set<Int> = emptySet(),
         filterTopicIds: Set<Int> = emptySet(),
     ): Flow<List<NewsResource>>
-
-    /**
-     * Synchronizes the local database in backing the repository with the network.
-     * Returns if the sync was successful or not.
-     */
-    suspend fun sync(): Boolean
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/TopicsRepository.kt

@@ -16,10 +16,11 @@
 
 package com.google.samples.apps.nowinandroid.core.domain.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Syncable
 import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import kotlinx.coroutines.flow.Flow
 
-interface TopicsRepository {
+interface TopicsRepository : Syncable {
     /**
      * Gets the available topics as a stream
      */
@@ -44,10 +45,4 @@ interface TopicsRepository {
      * Returns the users currently followed topics
      */
     fun getFollowedTopicIdsStream(): Flow<Set<Int>>
-
-    /**
-     * Synchronizes the local database in backing the repository with the network.
-     * Returns if the sync was successful or not.
-     */
-    suspend fun sync(): Boolean
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/fake/FakeAuthorsRepository.kt

@@ -17,6 +17,7 @@
 package com.google.samples.apps.nowinandroid.core.domain.repository.fake
 
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.AuthorsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.Author
 import com.google.samples.apps.nowinandroid.core.network.Dispatcher
@@ -68,5 +69,5 @@ class FakeAuthorsRepository @Inject constructor(
 
     override fun getFollowedAuthorIdsStream(): Flow<Set<Int>> = niaPreferences.followedAuthorIds
 
-    override suspend fun sync() = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/fake/FakeNewsRepository.kt

@@ -18,6 +18,7 @@ package com.google.samples.apps.nowinandroid.core.domain.repository.fake
 
 import com.google.samples.apps.nowinandroid.core.database.model.NewsResourceEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
 import com.google.samples.apps.nowinandroid.core.domain.repository.NewsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
@@ -71,5 +72,5 @@ class FakeNewsRepository @Inject constructor(
         }
             .flowOn(ioDispatcher)
 
-    override suspend fun sync() = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

core-domain/src/main/java/com/google/samples/apps/nowinandroid/core/domain/repository/fake/FakeTopicsRepository.kt

@@ -17,6 +17,7 @@
 package com.google.samples.apps.nowinandroid.core.domain.repository.fake
 
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.TopicsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import com.google.samples.apps.nowinandroid.core.network.Dispatcher
@@ -72,5 +73,5 @@ class FakeTopicsRepository @Inject constructor(
 
     override fun getFollowedTopicIdsStream() = niaPreferences.followedTopicIds
 
-    override suspend fun sync() = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalAuthorsRepositoryTest.kt

@@ -21,10 +21,14 @@ import com.google.samples.apps.nowinandroid.core.database.model.AuthorEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
 import com.google.samples.apps.nowinandroid.core.datastore.test.testUserPreferencesDataStore
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
+import com.google.samples.apps.nowinandroid.core.domain.testdoubles.CollectionType
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestAuthorDao
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestNiaNetwork
+import com.google.samples.apps.nowinandroid.core.model.data.Author
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkAuthor
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert
@@ -41,7 +45,7 @@ class LocalAuthorsRepositoryTest {
 
     private lateinit var network: TestNiaNetwork
 
-    private lateinit var niaPreferences: NiaPreferences
+    private lateinit var synchronizer: Synchronizer
 
     @get:Rule
     val tmpFolder: TemporaryFolder = TemporaryFolder.builder().assureDeletion().build()
@@ -50,9 +54,10 @@ class LocalAuthorsRepositoryTest {
     fun setup() {
         authorDao = TestAuthorDao()
         network = TestNiaNetwork()
-        niaPreferences = NiaPreferences(
+        val niaPreferences = NiaPreferences(
             tmpFolder.testUserPreferencesDataStore()
         )
+        synchronizer = TestSynchronizer(niaPreferences)
 
         subject = LocalAuthorsRepository(
             authorDao = authorDao,
@@ -76,23 +81,23 @@ class LocalAuthorsRepositoryTest {
     @Test
     fun localAuthorsRepository_sync_pulls_from_network() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
-            val network = network.getAuthors()
+            val networkAuthors = network.getAuthors()
                 .map(NetworkAuthor::asEntity)
 
-            val db = authorDao.getAuthorEntitiesStream()
+            val dbAuthors = authorDao.getAuthorEntitiesStream()
                 .first()
 
             Assert.assertEquals(
-                network.map(AuthorEntity::id),
+                networkAuthors.map(AuthorEntity::id),
-                db.map(AuthorEntity::id)
+                dbAuthors.map(AuthorEntity::id)
             )
 
             // After sync version should be updated
             Assert.assertEquals(
-                network.lastIndex,
+                network.latestChangeListVersion(CollectionType.Authors),
-                niaPreferences.getChangeListVersions().authorVersion
+                synchronizer.getChangeListVersions().authorVersion
             )
         }
 
@@ -100,16 +105,23 @@ class LocalAuthorsRepositoryTest {
     fun localAuthorsRepository_incremental_sync_pulls_from_network() =
         runTest {
             // Set author version to 5
-            niaPreferences.updateChangeListVersion {
+            synchronizer.updateChangeListVersions {
                 copy(authorVersion = 5)
             }
 
-            subject.sync()
+            subject.syncWith(synchronizer)
+
+            val changeList = network.changeListsAfter(
+                CollectionType.Authors,
+                version = 5
+            )
+            val changeListIds = changeList
+                .map(NetworkChangeList::id)
+                .toSet()
 
             val network = network.getAuthors()
                 .map(NetworkAuthor::asEntity)
-                // Drop 5 to simulate the first 5 items being unchanged
+                .filter { it.id in changeListIds }
-                .drop(5)
 
             val db = authorDao.getAuthorEntitiesStream()
                 .first()
@@ -121,8 +133,47 @@ class LocalAuthorsRepositoryTest {
 
             // After sync version should be updated
             Assert.assertEquals(
-                network.lastIndex + 5,
+                changeList.last().changeListVersion,
-                niaPreferences.getChangeListVersions().authorVersion
+                synchronizer.getChangeListVersions().authorVersion
+            )
+        }
+
+    @Test
+    fun localAuthorsRepository_sync_deletes_items_marked_deleted_on_network() =
+        runTest {
+            val networkAuthors = network.getAuthors()
+                .map(NetworkAuthor::asEntity)
+                .map(AuthorEntity::asExternalModel)
+
+            val deletedItems = networkAuthors
+                .map(Author::id)
+                .partition { it % 2 == 0 }
+                .first
+                .toSet()
+
+            deletedItems.forEach {
+                network.editCollection(
+                    collectionType = CollectionType.Authors,
+                    id = it,
+                    isDelete = true
+                )
+            }
+
+            subject.syncWith(synchronizer)
+
+            val dbAuthors = authorDao.getAuthorEntitiesStream()
+                .first()
+                .map(AuthorEntity::asExternalModel)
+
+            Assert.assertEquals(
+                networkAuthors.map(Author::id) - deletedItems,
+                dbAuthors.map(Author::id)
+            )
+
+            // After sync version should be updated
+            Assert.assertEquals(
+                network.latestChangeListVersion(CollectionType.Authors),
+                synchronizer.getChangeListVersions().authorVersion
             )
         }
 }

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalNewsRepositoryTest.kt

@@ -25,12 +25,14 @@ import com.google.samples.apps.nowinandroid.core.database.model.TopicEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
 import com.google.samples.apps.nowinandroid.core.datastore.test.testUserPreferencesDataStore
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
 import com.google.samples.apps.nowinandroid.core.domain.model.authorCrossReferences
 import com.google.samples.apps.nowinandroid.core.domain.model.authorEntityShells
 import com.google.samples.apps.nowinandroid.core.domain.model.episodeEntityShell
 import com.google.samples.apps.nowinandroid.core.domain.model.topicCrossReferences
 import com.google.samples.apps.nowinandroid.core.domain.model.topicEntityShells
+import com.google.samples.apps.nowinandroid.core.domain.testdoubles.CollectionType
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestAuthorDao
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestEpisodeDao
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestNewsResourceDao
@@ -39,6 +41,7 @@ import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestTopicDao
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.filteredInterestsIds
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.nonPresentInterestsIds
 import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkNewsResource
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
@@ -62,7 +65,7 @@ class LocalNewsRepositoryTest {
 
     private lateinit var network: TestNiaNetwork
 
-    private lateinit var niaPreferences: NiaPreferences
+    private lateinit var synchronizer: Synchronizer
 
     @get:Rule
     val tmpFolder: TemporaryFolder = TemporaryFolder.builder().assureDeletion().build()
@@ -74,8 +77,10 @@ class LocalNewsRepositoryTest {
         authorDao = TestAuthorDao()
         topicDao = TestTopicDao()
         network = TestNiaNetwork()
-        niaPreferences = NiaPreferences(
+        synchronizer = TestSynchronizer(
-            tmpFolder.testUserPreferencesDataStore()
+            NiaPreferences(
+                tmpFolder.testUserPreferencesDataStore()
+            )
         )
 
         subject = LocalNewsRepository(
@@ -84,7 +89,6 @@ class LocalNewsRepositoryTest {
             authorDao = authorDao,
             topicDao = topicDao,
             network = network,
-            niaPreferences = niaPreferences,
         )
     }
 
@@ -151,7 +155,7 @@ class LocalNewsRepositoryTest {
     @Test
     fun localNewsRepository_sync_pulls_from_network() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             val newsResourcesFromNetwork = network.getNewsResources()
                 .map(NetworkNewsResource::asEntity)
@@ -168,8 +172,47 @@ class LocalNewsRepositoryTest {
 
             // After sync version should be updated
             assertEquals(
-                newsResourcesFromNetwork.lastIndex,
+                network.latestChangeListVersion(CollectionType.NewsResources),
-                niaPreferences.getChangeListVersions().newsResourceVersion
+                synchronizer.getChangeListVersions().newsResourceVersion
+            )
+        }
+
+    @Test
+    fun localNewsRepository_sync_deletes_items_marked_deleted_on_network() =
+        runTest {
+            val newsResourcesFromNetwork = network.getNewsResources()
+                .map(NetworkNewsResource::asEntity)
+                .map(NewsResourceEntity::asExternalModel)
+
+            val deletedItems = newsResourcesFromNetwork
+                .map(NewsResource::id)
+                .partition { it % 2 == 0 }
+                .first
+                .toSet()
+
+            deletedItems.forEach {
+                network.editCollection(
+                    collectionType = CollectionType.NewsResources,
+                    id = it,
+                    isDelete = true
+                )
+            }
+
+            subject.syncWith(synchronizer)
+
+            val newsResourcesFromDb = newsResourceDao.getNewsResourcesStream()
+                .first()
+                .map(PopulatedNewsResource::asExternalModel)
+
+            assertEquals(
+                newsResourcesFromNetwork.map(NewsResource::id) - deletedItems,
+                newsResourcesFromDb.map(NewsResource::id)
+            )
+
+            // After sync version should be updated
+            assertEquals(
+                network.latestChangeListVersion(CollectionType.NewsResources),
+                synchronizer.getChangeListVersions().newsResourceVersion
             )
         }
 
@@ -177,17 +220,24 @@ class LocalNewsRepositoryTest {
     fun localNewsRepository_incremental_sync_pulls_from_network() =
         runTest {
             // Set news version to 7
-            niaPreferences.updateChangeListVersion {
+            synchronizer.updateChangeListVersions {
                 copy(newsResourceVersion = 7)
             }
 
-            subject.sync()
+            subject.syncWith(synchronizer)
+
+            val changeList = network.changeListsAfter(
+                CollectionType.NewsResources,
+                version = 7
+            )
+            val changeListIds = changeList
+                .map(NetworkChangeList::id)
+                .toSet()
 
             val newsResourcesFromNetwork = network.getNewsResources()
                 .map(NetworkNewsResource::asEntity)
                 .map(NewsResourceEntity::asExternalModel)
-                // Drop 7 to simulate the first 7 items being unchanged
+                .filter { it.id in changeListIds }
-                .drop(7)
 
             val newsResourcesFromDb = newsResourceDao.getNewsResourcesStream()
                 .first()
@@ -200,15 +250,15 @@ class LocalNewsRepositoryTest {
 
             // After sync version should be updated
             assertEquals(
-                newsResourcesFromNetwork.lastIndex + 7,
+                changeList.last().changeListVersion,
-                niaPreferences.getChangeListVersions().newsResourceVersion
+                synchronizer.getChangeListVersions().newsResourceVersion
             )
         }
 
     @Test
     fun localNewsRepository_sync_saves_shell_topic_entities() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             assertEquals(
                 network.getNewsResources()
@@ -223,7 +273,7 @@ class LocalNewsRepositoryTest {
     @Test
     fun localNewsRepository_sync_saves_shell_author_entities() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             assertEquals(
                 network.getNewsResources()
@@ -238,7 +288,7 @@ class LocalNewsRepositoryTest {
     @Test
     fun localNewsRepository_sync_saves_shell_episode_entities() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             assertEquals(
                 network.getNewsResources()
@@ -253,7 +303,7 @@ class LocalNewsRepositoryTest {
     @Test
     fun localNewsRepository_sync_saves_topic_cross_references() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             assertEquals(
                 network.getNewsResources()
@@ -267,7 +317,7 @@ class LocalNewsRepositoryTest {
     @Test
     fun localNewsRepository_sync_saves_author_cross_references() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
             assertEquals(
                 network.getNewsResources()

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/repository/LocalTopicsRepositoryTest.kt

@@ -21,10 +21,12 @@ import com.google.samples.apps.nowinandroid.core.database.model.TopicEntity
 import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
 import com.google.samples.apps.nowinandroid.core.datastore.test.testUserPreferencesDataStore
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.model.asEntity
+import com.google.samples.apps.nowinandroid.core.domain.testdoubles.CollectionType
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestNiaNetwork
 import com.google.samples.apps.nowinandroid.core.domain.testdoubles.TestTopicDao
-import com.google.samples.apps.nowinandroid.core.network.NiANetwork
+import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkTopic
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
@@ -40,10 +42,12 @@ class LocalTopicsRepositoryTest {
 
     private lateinit var topicDao: TopicDao
 
-    private lateinit var network: NiANetwork
+    private lateinit var network: TestNiaNetwork
 
     private lateinit var niaPreferences: NiaPreferences
 
+    private lateinit var synchronizer: Synchronizer
+
     @get:Rule
     val tmpFolder: TemporaryFolder = TemporaryFolder.builder().assureDeletion().build()
 
@@ -54,6 +58,7 @@ class LocalTopicsRepositoryTest {
         niaPreferences = NiaPreferences(
             tmpFolder.testUserPreferencesDataStore()
         )
+        synchronizer = TestSynchronizer(niaPreferences)
 
         subject = LocalTopicsRepository(
             topicDao = topicDao,
@@ -88,23 +93,23 @@ class LocalTopicsRepositoryTest {
     @Test
     fun localTopicsRepository_sync_pulls_from_network() =
         runTest {
-            subject.sync()
+            subject.syncWith(synchronizer)
 
-            val network = network.getTopics()
+            val networkTopics = network.getTopics()
                 .map(NetworkTopic::asEntity)
 
-            val db = topicDao.getTopicEntitiesStream()
+            val dbTopics = topicDao.getTopicEntitiesStream()
                 .first()
 
             Assert.assertEquals(
-                network.map(TopicEntity::id),
+                networkTopics.map(TopicEntity::id),
-                db.map(TopicEntity::id)
+                dbTopics.map(TopicEntity::id)
             )
 
             // After sync version should be updated
             Assert.assertEquals(
-                network.lastIndex,
+                network.latestChangeListVersion(CollectionType.Topics),
-                niaPreferences.getChangeListVersions().topicVersion
+                synchronizer.getChangeListVersions().topicVersion
             )
         }
 
@@ -112,29 +117,68 @@ class LocalTopicsRepositoryTest {
     fun localTopicsRepository_incremental_sync_pulls_from_network() =
         runTest {
             // Set topics version to 10
-            niaPreferences.updateChangeListVersion {
+            synchronizer.updateChangeListVersions {
                 copy(topicVersion = 10)
             }
 
-            subject.sync()
+            subject.syncWith(synchronizer)
 
-            val network = network.getTopics()
+            val networkTopics = network.getTopics()
                 .map(NetworkTopic::asEntity)
                 // Drop 10 to simulate the first 10 items being unchanged
                 .drop(10)
 
-            val db = topicDao.getTopicEntitiesStream()
+            val dbTopics = topicDao.getTopicEntitiesStream()
+                .first()
+
+            Assert.assertEquals(
+                networkTopics.map(TopicEntity::id),
+                dbTopics.map(TopicEntity::id)
+            )
+
+            // After sync version should be updated
+            Assert.assertEquals(
+                network.latestChangeListVersion(CollectionType.Topics),
+                synchronizer.getChangeListVersions().topicVersion
+            )
+        }
+
+    @Test
+    fun localTopicsRepository_sync_deletes_items_marked_deleted_on_network() =
+        runTest {
+            val networkTopics = network.getTopics()
+                .map(NetworkTopic::asEntity)
+                .map(TopicEntity::asExternalModel)
+
+            val deletedItems = networkTopics
+                .map(Topic::id)
+                .partition { it % 2 == 0 }
+                .first
+                .toSet()
+
+            deletedItems.forEach {
+                network.editCollection(
+                    collectionType = CollectionType.Topics,
+                    id = it,
+                    isDelete = true
+                )
+            }
+
+            subject.syncWith(synchronizer)
+
+            val dbTopics = topicDao.getTopicEntitiesStream()
                 .first()
+                .map(TopicEntity::asExternalModel)
 
             Assert.assertEquals(
-                network.map(TopicEntity::id),
+                networkTopics.map(Topic::id) - deletedItems,
-                db.map(TopicEntity::id)
+                dbTopics.map(Topic::id)
             )
 
             // After sync version should be updated
             Assert.assertEquals(
-                network.lastIndex + 10,
+                network.latestChangeListVersion(CollectionType.Topics),
-                niaPreferences.getChangeListVersions().topicVersion
+                synchronizer.getChangeListVersions().topicVersion
             )
         }
 

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/repository/TestSynchronizer.kt

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2022 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.domain.repository
+
+import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
+import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
+
+/**
+ * Test synchronizer that delegates to [NiaPreferences]
+ */
+class TestSynchronizer(
+    private val niaPreferences: NiaPreferences
+) : Synchronizer {
+    override suspend fun getChangeListVersions(): ChangeListVersions =
+        niaPreferences.getChangeListVersions()
+
+    override suspend fun updateChangeListVersions(
+        update: ChangeListVersions.() -> ChangeListVersions
+    ) = niaPreferences.updateChangeListVersion(update)
+}

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/testdoubles/TestAuthorDao.kt

@@ -20,6 +20,7 @@ import com.google.samples.apps.nowinandroid.core.database.dao.AuthorDao
 import com.google.samples.apps.nowinandroid.core.database.model.AuthorEntity
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.update
 
 /**
  * Test double for [AuthorDao]
@@ -50,4 +51,11 @@ class TestAuthorDao : AuthorDao {
     override suspend fun updateAuthors(entities: List<AuthorEntity>) {
         throw NotImplementedError("Unused in tests")
     }
+
+    override suspend fun deleteAuthors(ids: List<Int>) {
+        val idSet = ids.toSet()
+        entitiesStateFlow.update { entities ->
+            entities.filterNot { idSet.contains(it.id) }
+        }
+    }
 }

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/testdoubles/TestEpisodeDao.kt

@@ -22,6 +22,7 @@ import com.google.samples.apps.nowinandroid.core.database.model.PopulatedEpisode
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.update
 import kotlinx.datetime.Instant
 
 /**
@@ -55,6 +56,13 @@ class TestEpisodeDao : EpisodeDao {
     override suspend fun updateEpisodes(entities: List<EpisodeEntity>) {
         throw NotImplementedError("Unused in tests")
     }
+
+    override suspend fun deleteEpisodes(ids: List<Int>) {
+        val idSet = ids.toSet()
+        entitiesStateFlow.update { entities ->
+            entities.filterNot { idSet.contains(it.id) }
+        }
+    }
 }
 
 private fun EpisodeEntity.asPopulatedEpisode() = PopulatedEpisode(

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/testdoubles/TestNewsResourceDao.kt

@@ -28,6 +28,7 @@ import com.google.samples.apps.nowinandroid.core.model.data.NewsResourceType.Vid
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.update
 import kotlinx.datetime.Instant
 
 val filteredInterestsIds = setOf(1)
@@ -97,6 +98,13 @@ class TestNewsResourceDao : NewsResourceDao {
     ) {
         authorCrossReferences = newsResourceAuthorCrossReferences
     }
+
+    override suspend fun deleteNewsResources(ids: List<Int>) {
+        val idSet = ids.toSet()
+        entitiesStateFlow.update { entities ->
+            entities.filterNot { idSet.contains(it.id) }
+        }
+    }
 }
 
 private fun NewsResourceEntity.asPopulatedNewsResource() = PopulatedNewsResource(

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/testdoubles/TestNiaNetwork.kt

@@ -25,6 +25,13 @@ import com.google.samples.apps.nowinandroid.core.network.model.NetworkTopic
 import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.json.Json
 
+enum class CollectionType {
+    Topics,
+    Authors,
+    Episodes,
+    NewsResources
+}
+
 /**
  * Test double for [NiANetwork]
  */
@@ -32,46 +39,80 @@ class TestNiaNetwork : NiANetwork {
 
     private val networkJson = Json
 
-    override suspend fun getTopics(ids: List<Int>?): List<NetworkTopic> =
+    private val allTopics =
         networkJson.decodeFromString<List<NetworkTopic>>(FakeDataSource.topicsData)
-            .matchIds(
-                ids = ids,
-                idGetter = NetworkTopic::id
-            )
 
-    override suspend fun getAuthors(ids: List<Int>?): List<NetworkAuthor> =
+    private val allAuthors =
         networkJson.decodeFromString<List<NetworkAuthor>>(FakeDataSource.authors)
-            .matchIds(
-                ids = ids,
-                idGetter = NetworkAuthor::id
-            )
 
-    override suspend fun getNewsResources(ids: List<Int>?): List<NetworkNewsResource> =
+    private val allNewsResources =
         networkJson.decodeFromString<List<NetworkNewsResource>>(FakeDataSource.data)
-            .matchIds(
-                ids = ids,
-                idGetter = NetworkNewsResource::id
-            )
 
-    override suspend fun getTopicChangeList(after: Int?): List<NetworkChangeList> =
+    private val changeLists: MutableMap<CollectionType, List<NetworkChangeList>> = mutableMapOf(
-        getTopics(ids = null).mapToChangeList(
+        CollectionType.Topics to allTopics
-            after = after,
+            .mapToChangeList(idGetter = NetworkTopic::id),
+        CollectionType.Authors to allAuthors
+            .mapToChangeList(idGetter = NetworkAuthor::id),
+        CollectionType.Episodes to listOf(),
+        CollectionType.NewsResources to allNewsResources
+            .mapToChangeList(idGetter = NetworkNewsResource::id),
+    )
+
+    override suspend fun getTopics(ids: List<Int>?): List<NetworkTopic> =
+        allTopics.matchIds(
+            ids = ids,
             idGetter = NetworkTopic::id
         )
 
-    override suspend fun getAuthorChangeList(after: Int?): List<NetworkChangeList> =
+    override suspend fun getAuthors(ids: List<Int>?): List<NetworkAuthor> =
-        getAuthors(ids = null).mapToChangeList(
+        allAuthors.matchIds(
-            after = after,
+            ids = ids,
             idGetter = NetworkAuthor::id
         )
 
-    override suspend fun getNewsResourceChangeList(after: Int?): List<NetworkChangeList> =
+    override suspend fun getNewsResources(ids: List<Int>?): List<NetworkNewsResource> =
-        getNewsResources(ids = null).mapToChangeList(
+        allNewsResources.matchIds(
-            after = after,
+            ids = ids,
             idGetter = NetworkNewsResource::id
         )
+
+    override suspend fun getTopicChangeList(after: Int?): List<NetworkChangeList> =
+        changeLists.getValue(CollectionType.Topics).after(after)
+
+    override suspend fun getAuthorChangeList(after: Int?): List<NetworkChangeList> =
+        changeLists.getValue(CollectionType.Authors).after(after)
+
+    override suspend fun getNewsResourceChangeList(after: Int?): List<NetworkChangeList> =
+        changeLists.getValue(CollectionType.NewsResources).after(after)
+
+    fun latestChangeListVersion(collectionType: CollectionType) =
+        changeLists.getValue(collectionType).last().changeListVersion
+
+    fun changeListsAfter(collectionType: CollectionType, version: Int) =
+        changeLists.getValue(collectionType).after(version)
+
+    /**
+     * Edits the change list for the backing [collectionType] for the given [id] mimicking
+     * the server's change list registry
+     */
+    fun editCollection(collectionType: CollectionType, id: Int, isDelete: Boolean) {
+        val changeList = changeLists.getValue(collectionType)
+        val latestVersion = changeList.lastOrNull()?.changeListVersion ?: 0
+        val change = NetworkChangeList(
+            id = id,
+            isDelete = isDelete,
+            changeListVersion = latestVersion + 1,
+        )
+        changeLists[collectionType] = changeList.filterNot { it.id == id } + change
+    }
 }
 
+fun List<NetworkChangeList>.after(version: Int?): List<NetworkChangeList> =
+    when (version) {
+        null -> this
+        else -> this.filter { it.changeListVersion > version }
+    }
+
 /**
  * Return items from [this] whose id defined by [idGetter] is in [ids] if [ids] is not null
  */
@@ -88,12 +129,11 @@ private fun <T> List<T>.matchIds(
  * [after] simulates which models have changed by excluding items before it
  */
 private fun <T> List<T>.mapToChangeList(
-    after: Int?,
     idGetter: (T) -> Int
 ) = mapIndexed { index, item ->
     NetworkChangeList(
         id = idGetter(item),
-        changeListVersion = index,
+        changeListVersion = index + 1,
         isDelete = false,
     )
-}.drop(after ?: 0)
+}

core-domain/src/test/java/com/google/samples/apps/nowinandroid/core/domain/testdoubles/TestTopicDao.kt

@@ -21,6 +21,7 @@ import com.google.samples.apps.nowinandroid.core.database.model.TopicEntity
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.update
 
 /**
  * Test double for [TopicDao]
@@ -60,4 +61,11 @@ class TestTopicDao : TopicDao {
     override suspend fun updateTopics(entities: List<TopicEntity>) {
         throw NotImplementedError("Unused in tests")
     }
+
+    override suspend fun deleteTopics(ids: List<Int>) {
+        val idSet = ids.toSet()
+        entitiesStateFlow.update { entities ->
+            entities.filterNot { idSet.contains(it.id) }
+        }
+    }
 }

core-network/src/main/java/com/google/samples/apps/nowinandroid/core/network/model/NetworkChangeList.kt

@@ -19,11 +19,25 @@ package com.google.samples.apps.nowinandroid.core.network.model
 import kotlinx.serialization.Serializable
 
 /**
- * Network representation of a change list for a model
+ * Network representation of a change list for a model.
+ *
+ * Change lists are a representation of a server-side map like data structure of model ids to
+ * metadata about that model. In a single change list, a given model id can only show up once.
  */
 @Serializable
 data class NetworkChangeList(
+    /**
+     * The id of the model that was changed
+     */
     val id: Int,
+    /**
+     * Unique consecutive, monotonically increasing version number in the collection describing
+     * the relative point of change between models in the collection
+     */
     val changeListVersion: Int,
+    /**
+     * Summarizes the update to the model; whether it was deleted or updated.
+     * Updates include creations.
+     */
     val isDelete: Boolean,
 )

core-testing/src/main/java/com/google/samples/apps/nowinandroid/core/testing/repository/TestAuthorsRepository.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.core.testing.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.AuthorsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.Author
 import kotlinx.coroutines.channels.BufferOverflow
@@ -52,7 +53,7 @@ class TestAuthorsRepository : AuthorsRepository {
         }
     }
 
-    override suspend fun sync(): Boolean = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 
     /**
      * A test-only API to allow controlling the list of topics from tests.

core-testing/src/main/java/com/google/samples/apps/nowinandroid/core/testing/repository/TestNewsRepository.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.core.testing.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.NewsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.Author
 import com.google.samples.apps.nowinandroid.core.model.data.NewsResource
@@ -54,5 +55,5 @@ class TestNewsRepository : NewsRepository {
         newsResourcesFlow.tryEmit(newsResources)
     }
 
-    override suspend fun sync(): Boolean = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

core-testing/src/main/java/com/google/samples/apps/nowinandroid/core/testing/repository/TestTopicsRepository.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.core.testing.repository
 
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.TopicsRepository
 import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import kotlinx.coroutines.channels.BufferOverflow
@@ -69,5 +70,5 @@ class TestTopicsRepository : TopicsRepository {
      */
     fun getCurrentFollowedTopics(): Set<Int>? = _followedTopicIds.replayCache.firstOrNull()
 
-    override suspend fun sync(): Boolean = true
+    override suspend fun syncWith(synchronizer: Synchronizer) = true
 }

sync/src/main/java/com/google/samples/apps/nowinandroid/sync/initializers/SyncInitializer.kt

@@ -19,7 +19,7 @@ package com.google.samples.apps.nowinandroid.sync.initializers
 import android.content.Context
 import androidx.startup.AppInitializer
 import androidx.startup.Initializer
-import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.ExistingWorkPolicy
 import androidx.work.WorkManager
 import androidx.work.WorkManagerInitializer
 import com.google.samples.apps.nowinandroid.sync.workers.SyncWorker
@@ -43,11 +43,11 @@ private const val SyncWorkName = "SyncWorkName"
 class SyncInitializer : Initializer<Sync> {
     override fun create(context: Context): Sync {
         WorkManager.getInstance(context).apply {
-            enqueue(SyncWorker.startUpSyncWork())
+            // Run sync on app startup and ensure only one sync worker runs at any time
-            enqueueUniquePeriodicWork(
+            enqueueUniqueWork(
                 SyncWorkName,
-                ExistingPeriodicWorkPolicy.KEEP,
+                ExistingWorkPolicy.REPLACE,
-                SyncWorker.periodicSyncWork()
+                SyncWorker.startUpSyncWork()
             )
         }
 

sync/src/main/java/com/google/samples/apps/nowinandroid/sync/workers/SyncWorker.kt

@@ -22,8 +22,10 @@ import androidx.work.CoroutineWorker
 import androidx.work.ForegroundInfo
 import androidx.work.OneTimeWorkRequestBuilder
 import androidx.work.OutOfQuotaPolicy
-import androidx.work.PeriodicWorkRequestBuilder
 import androidx.work.WorkerParameters
+import com.google.samples.apps.nowinandroid.core.datastore.ChangeListVersions
+import com.google.samples.apps.nowinandroid.core.datastore.NiaPreferences
+import com.google.samples.apps.nowinandroid.core.domain.Synchronizer
 import com.google.samples.apps.nowinandroid.core.domain.repository.AuthorsRepository
 import com.google.samples.apps.nowinandroid.core.domain.repository.NewsRepository
 import com.google.samples.apps.nowinandroid.core.domain.repository.TopicsRepository
@@ -31,7 +33,6 @@ import com.google.samples.apps.nowinandroid.sync.initializers.SyncConstraints
 import com.google.samples.apps.nowinandroid.sync.initializers.syncForegroundInfo
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedInject
-import java.util.concurrent.TimeUnit
 import kotlinx.coroutines.async
 import kotlinx.coroutines.awaitAll
 import kotlinx.coroutines.coroutineScope
@@ -44,10 +45,11 @@ import kotlinx.coroutines.coroutineScope
 class SyncWorker @AssistedInject constructor(
     @Assisted private val appContext: Context,
     @Assisted workerParams: WorkerParameters,
+    private val niaPreferences: NiaPreferences,
     private val topicRepository: TopicsRepository,
     private val newsRepository: NewsRepository,
     private val authorsRepository: AuthorsRepository,
-) : CoroutineWorker(appContext, workerParams) {
+) : CoroutineWorker(appContext, workerParams), Synchronizer {
 
     override suspend fun getForegroundInfo(): ForegroundInfo =
         appContext.syncForegroundInfo()
@@ -64,10 +66,14 @@ class SyncWorker @AssistedInject constructor(
         else Result.retry()
     }
 
-    companion object {
+    override suspend fun getChangeListVersions(): ChangeListVersions =
-        private const val SyncInterval = 1L
+        niaPreferences.getChangeListVersions()
-        private val SyncIntervalTimeUnit = TimeUnit.DAYS
+
+    override suspend fun updateChangeListVersions(
+        update: ChangeListVersions.() -> ChangeListVersions
+    ) = niaPreferences.updateChangeListVersion(update)
 
+    companion object {
         /**
          * Expedited one time work to sync data on app startup
          */
@@ -76,16 +82,5 @@ class SyncWorker @AssistedInject constructor(
             .setConstraints(SyncConstraints)
             .setInputData(SyncWorker::class.delegatedData())
             .build()
-
-        /**
-         * Periodic sync work to routinely keep the app up to date
-         */
-        fun periodicSyncWork() = PeriodicWorkRequestBuilder<DelegatingWorker>(
-            SyncInterval,
-            SyncIntervalTimeUnit
-        )
-            .setConstraints(SyncConstraints)
-            .setInputData(SyncWorker::class.delegatedData())
-            .build()
     }
 }