feat(views): customizable quick-switch cycle + drawer order (#24)

Add a "Views" settings section that lets users pick which views the
top-bar quick-switch button cycles through and drag to reorder them,
plus an independent drag-to-reorder for the navigation drawer's view
list. Two separate configs: a view turned off in the quick-switch
cycle is still reachable from the drawer, which always lists every view.

- QuickSwitchConfig (order + enabled set) and a drawer order persisted
  in SettingsPrefs (comma-joined enum names; "!" marks a disabled view).
  Missing views append enabled and unknown names drop, so a future view
  defaults into both lists.
- The pill cycles through the configured enabled views in order; the
  drawer renders CalendarDrawer from the drawer order. Both threaded
  from CalendarHost via CalendarHostViewModel.
- New ReorderableColumn: dependency-free, measurement-driven drag
  reordering for the short grouped-card settings lists (no LazyColumn,
  since settings are a single verticalScroll column). Commits one write
  per gesture.
- The switch needs two targets, so the last two enabled views can't be
  turned off.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/calendula/data/prefs/SettingsPrefsTest.kt

@@ -6,6 +6,9 @@ import androidx.datastore.preferences.core.Preferences
 import com.google.common.truth.Truth.assertThat
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.ui.agenda.AgendaRange
+import de.jeanlucmakiola.calendula.ui.common.CalendarView
+import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
+import de.jeanlucmakiola.calendula.ui.common.QuickSwitchConfig
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
 import kotlinx.datetime.DayOfWeek
@@ -149,6 +152,78 @@ class SettingsPrefsTest {
         assertThat(prefs.defaultFormFields.first()).isEmpty()
     }
 
+    @Test
+    fun `quick-switch defaults to every view enabled in default order`(@TempDir tempDir: Path) = runTest {
+        val prefs = SettingsPrefs(newDataStore(tempDir))
+        val config = prefs.quickSwitchConfig.first()
+        assertThat(config.order).containsExactlyElementsIn(IMPLEMENTED_VIEWS).inOrder()
+        assertThat(config.enabled).containsExactlyElementsIn(IMPLEMENTED_VIEWS)
+        assertThat(config.cycle).containsExactlyElementsIn(IMPLEMENTED_VIEWS).inOrder()
+    }
+
+    @Test
+    fun `quick-switch config round-trips order and disabled views`(@TempDir tempDir: Path) = runTest {
+        val prefs = SettingsPrefs(newDataStore(tempDir))
+        val config = QuickSwitchConfig(
+            order = listOf(CalendarView.Agenda, CalendarView.Month, CalendarView.Week, CalendarView.Day),
+            enabled = setOf(CalendarView.Agenda, CalendarView.Month),
+        )
+        prefs.setQuickSwitchConfig(config)
+        val loaded = prefs.quickSwitchConfig.first()
+        assertThat(loaded.order).containsExactly(
+            CalendarView.Agenda, CalendarView.Month, CalendarView.Week, CalendarView.Day,
+        ).inOrder()
+        assertThat(loaded.enabled).containsExactly(CalendarView.Agenda, CalendarView.Month)
+        assertThat(loaded.cycle).containsExactly(CalendarView.Agenda, CalendarView.Month).inOrder()
+    }
+
+    @Test
+    fun `quick-switch parse appends missing views enabled and drops unknowns`(@TempDir tempDir: Path) = runTest {
+        val store = newDataStore(tempDir)
+        val prefs = SettingsPrefs(store)
+        // Only Day (disabled) and Week stored, plus a bogus name; Month & Agenda absent.
+        store.updateData { p ->
+            val m = p.toMutablePreferences()
+            m[SettingsPrefs.QUICK_SWITCH_VIEWS_KEY] = "!Day,Week,Hologram"
+            m
+        }
+        val config = prefs.quickSwitchConfig.first()
+        // Stored order first (Day, Week), then the omitted views in default order.
+        assertThat(config.order).containsExactly(
+            CalendarView.Day, CalendarView.Week, CalendarView.Month, CalendarView.Agenda,
+        ).inOrder()
+        // Day was explicitly disabled; the appended Month & Agenda default enabled.
+        assertThat(config.enabled).containsExactly(
+            CalendarView.Week, CalendarView.Month, CalendarView.Agenda,
+        )
+    }
+
+    @Test
+    fun `drawer order defaults to the implemented order and round-trips`(@TempDir tempDir: Path) = runTest {
+        val prefs = SettingsPrefs(newDataStore(tempDir))
+        assertThat(prefs.drawerViewOrder.first()).containsExactlyElementsIn(IMPLEMENTED_VIEWS).inOrder()
+        prefs.setDrawerViewOrder(
+            listOf(CalendarView.Agenda, CalendarView.Day, CalendarView.Week, CalendarView.Month),
+        )
+        assertThat(prefs.drawerViewOrder.first()).containsExactly(
+            CalendarView.Agenda, CalendarView.Day, CalendarView.Week, CalendarView.Month,
+        ).inOrder()
+    }
+
+    @Test
+    fun `drawer order parse appends missing views and drops unknowns`(@TempDir tempDir: Path) = runTest {
+        val store = newDataStore(tempDir)
+        val prefs = SettingsPrefs(store)
+        store.updateData { p ->
+            val m = p.toMutablePreferences()
+            m[SettingsPrefs.DRAWER_VIEW_ORDER_KEY] = "Agenda,Nope,Week"
+            m
+        }
+        assertThat(prefs.drawerViewOrder.first()).containsExactly(
+            CalendarView.Agenda, CalendarView.Week, CalendarView.Month, CalendarView.Day,
+        ).inOrder()
+    }
+
     @Test
     fun `unknown stored form-field names are dropped`(@TempDir tempDir: Path) = runTest {
         val store = newDataStore(tempDir)

app/src/test/java/de/jeanlucmakiola/calendula/ui/common/ViewBackStackTest.kt

@@ -91,4 +91,33 @@ class ViewBackStackTest {
         assertThat(viewBaseStack(CalendarView.Agenda, CalendarView.Agenda))
             .containsExactly(CalendarView.Agenda)
     }
+
+    @Test
+    fun `next cycles through the configured views in order, wrapping around`() {
+        val cycle = listOf(CalendarView.Month, CalendarView.Agenda)
+        assertThat(CalendarView.Month.next(cycle)).isEqualTo(CalendarView.Agenda)
+        // Wraps back to the first from the last.
+        assertThat(CalendarView.Agenda.next(cycle)).isEqualTo(CalendarView.Month)
+    }
+
+    @Test
+    fun `next from a view outside the cycle lands on the first enabled view`() {
+        // Day was disabled in the quick-switch cycle but is still the current view.
+        val cycle = listOf(CalendarView.Week, CalendarView.Month)
+        assertThat(CalendarView.Day.next(cycle)).isEqualTo(CalendarView.Week)
+    }
+
+    @Test
+    fun `next on an empty cycle stays put`() {
+        assertThat(CalendarView.Week.next(emptyList())).isEqualTo(CalendarView.Week)
+    }
+
+    @Test
+    fun `quick-switch cycle keeps enabled views in their configured order`() {
+        val config = QuickSwitchConfig(
+            order = listOf(CalendarView.Agenda, CalendarView.Day, CalendarView.Month, CalendarView.Week),
+            enabled = setOf(CalendarView.Agenda, CalendarView.Month),
+        )
+        assertThat(config.cycle).containsExactly(CalendarView.Agenda, CalendarView.Month).inOrder()
+    }
 }