feat: add selection state to BookmarksViewModel with enter/exit/toggle/selectAll

Co-Authored-By: Claude <noreply@anthropic.com>

feature/bookmarks/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/BookmarksViewModel.kt

@@ -44,6 +44,31 @@ class BookmarksViewModel @Inject constructor(
     var shouldDisplayUndoBookmark by mutableStateOf(false)
     private var lastRemovedBookmarkId: String? = null
 
+    var isInSelectionMode by mutableStateOf(false)
+        private set
+
+    var selectedIds by mutableStateOf(emptySet<String>())
+        private set
+
+    fun enterSelectionMode(initialId: String) {
+        isInSelectionMode = true
+        selectedIds = setOf(initialId)
+    }
+
+    fun exitSelectionMode() {
+        isInSelectionMode = false
+        selectedIds = emptySet()
+    }
+
+    fun toggleSelection(id: String) {
+        selectedIds = if (id in selectedIds) selectedIds - id else selectedIds + id
+    }
+
+    fun selectAll() {
+        val currentFeed = (feedUiState.value as? NewsFeedUiState.Success)?.feed ?: return
+        selectedIds = currentFeed.map { it.id }.toSet()
+    }
+
     val feedUiState: StateFlow<NewsFeedUiState> =
         userNewsResourceRepository.observeAllBookmarked()
             .map<List<UserNewsResource>, NewsFeedUiState>(NewsFeedUiState::Success)

feature/bookmarks/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/BookmarksViewModelTest.kt

@@ -112,6 +112,30 @@ class BookmarksViewModelTest {
         assertTrue(item.feed.first().hasBeenViewed)
     }
 
+    @Test
+    fun enterSelectionMode_setsSelectedId() = runTest {
+        viewModel.enterSelectionMode("news1")
+        assertTrue(viewModel.isInSelectionMode)
+        assertEquals(setOf("news1"), viewModel.selectedIds)
+    }
+
+    @Test
+    fun toggleSelection_addsAndRemovesId() = runTest {
+        viewModel.enterSelectionMode("news1")
+        viewModel.toggleSelection("news2")
+        assertEquals(setOf("news1", "news2"), viewModel.selectedIds)
+        viewModel.toggleSelection("news1")
+        assertEquals(setOf("news2"), viewModel.selectedIds)
+    }
+
+    @Test
+    fun exitSelectionMode_clearsState() = runTest {
+        viewModel.enterSelectionMode("news1")
+        viewModel.exitSelectionMode()
+        assertFalse(viewModel.isInSelectionMode)
+        assertTrue(viewModel.selectedIds.isEmpty())
+    }
+
     @Test
     fun feedUiState_undoneBookmarkRemoval_bookmarkIsRestored() = runTest {
         backgroundScope.launch(UnconfinedTestDispatcher()) { viewModel.feedUiState.collect() }