Keep the move action and default off while unknown (#173)

Switching drag off gated the whole move scope, which also removed the
TalkBack move action — a menu item can't cause an accidental drag, so it
stays; only the gesture is gated now, via EventMoveScope.dragEnabled.

The host flow also started at true, re-arming the gesture for the first
frames of a cold start for exactly the user who turned it off.

app/src/main/java/de/jeanlucmakiola/calendula/ui/CalendarHost.kt

@@ -312,12 +312,13 @@ fun CalendarHost(
         heldEditKey = key
         editKey = key
     }
-    // Off by preference (#173) means no scope at all: every block then registers
+    // Off by preference (#173) switches off the gesture, not the scope: blocks
-    // no drag gesture, and the edit form stays the way to reschedule.
+    // register no drag, while the edit form and its TalkBack action stay put.
     val dragToReschedule = viewModel.dragToReschedule.collectAsStateWithLifecycle().value
-    val moveScope = remember(movableCalendarIds, reschedule) {
+    val moveScope = remember(movableCalendarIds, reschedule, dragToReschedule) {
         EventMoveScope(
             movableCalendarIds = movableCalendarIds,
+            dragEnabled = dragToReschedule,
             move = reschedule::move,
             inFlight = reschedule.inFlight,
             undoStarted = reschedule.undoStarted,
@@ -342,7 +343,7 @@ fun CalendarHost(
         // navigation, so it fades through rather than sliding — paging *within* a
         // view keeps the directional slide. AnimatedContent keyed on the view type.
         val viewSwitch = fadeThrough()
-        CompositionLocalProvider(LocalEventMove provides moveScope.takeIf { dragToReschedule }) {
+        CompositionLocalProvider(LocalEventMove provides moveScope) {
         AnimatedContent(
             targetState = view,
             transitionSpec = { viewSwitch },

app/src/main/java/de/jeanlucmakiola/calendula/ui/CalendarHostViewModel.kt

@@ -54,11 +54,17 @@ class CalendarHostViewModel @Inject constructor(
             initialValue = false,
         )
 
-    /** Whether events may be dragged to another slot to reschedule them (#68, #173). */
+    /**
+     * Whether events may be dragged to another slot to reschedule them (#68, #173).
+     * Off until the stored value arrives, even though the preference itself defaults
+     * on: the wrong guess costs an enabled user a gesture for the few frames a cold
+     * start takes to read DataStore, but re-arms the one thing a disabled user
+     * switched off to be rid of.
+     */
     val dragToReschedule: StateFlow<Boolean> = prefs.dragToReschedule
         .stateIn(
             scope = viewModelScope,
             started = SharingStarted.WhileSubscribed(5_000L),
-            initialValue = true,
+            initialValue = false,
         )
 }

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/EventMoveScope.kt

@@ -29,6 +29,12 @@ class EventMoveScope(
      * the repository writes whatever it is handed — so this gate is load-bearing.
      */
     val movableCalendarIds: Set<Long>,
+    /**
+     * Whether the *gesture* is on (#173). Off gates the drag alone: [edit] and the
+     * TalkBack action below stay, since invoking a menu item can't cause the
+     * accidental drags the setting exists to stop.
+     */
+    val dragEnabled: Boolean,
     /** False when the drop was refused outright, so nothing will be written. */
     val move: (MoveRequest) -> Boolean,
     /**
@@ -91,6 +97,17 @@ fun ghostAlpha(lifted: Boolean): Float = animateFloatAsState(
     label = "ghost-alpha",
 ).value
 
+/**
+ * Whether [event] can be picked up and dragged — its calendar allows moving and
+ * the gesture is switched on. Not the same question as [eventMoveAction], which
+ * survives the setting.
+ */
+@Composable
+fun eventDragAllowed(event: EventInstance): Boolean {
+    val move = LocalEventMove.current ?: return false
+    return move.dragEnabled && move.allows(event)
+}
+
 /**
  * A TalkBack action that opens [event] in the edit form, so rescheduling isn't
  * pointer-only. Null when this event can't be moved.

app/src/main/java/de/jeanlucmakiola/calendula/ui/day/DayScreen.kt

@@ -92,6 +92,7 @@ import de.jeanlucmakiola.calendula.ui.common.TimelineDragController
 import de.jeanlucmakiola.calendula.ui.common.TimelineDragOverlay
 import de.jeanlucmakiola.calendula.ui.common.TimelineDrop
 import de.jeanlucmakiola.calendula.ui.common.beginsOn
+import de.jeanlucmakiola.calendula.ui.common.eventDragAllowed
 import de.jeanlucmakiola.calendula.ui.common.eventMoveAction
 import de.jeanlucmakiola.calendula.ui.common.rememberEventDragSource
 import de.jeanlucmakiola.calendula.ui.common.rememberTimelineDragController
@@ -737,7 +738,7 @@ private fun EventBlock(
     val moveAction = eventMoveAction(block.event)
     // A block clipped at the top continues from the previous day: its top edge
     // is midnight, not the event's start, so dragging it would invent a time.
-    val draggable = moveAction != null && block.beginsOn(date, zone)
+    val draggable = eventDragAllowed(block.event) && block.beginsOn(date, zone)
     val dragModifier = rememberEventDragSource(
         enabled = draggable,
         key = block.event.instanceId,

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthScreen.kt

@@ -2172,7 +2172,7 @@ private fun monthChipDragModifier(
     rowHeightPx: Float,
     isRtl: Boolean,
 ): Modifier = rememberDragSurface(
-    enabled = moveScope != null && controller != null,
+    enabled = moveScope?.dragEnabled == true && controller != null,
     key = week.days.first(),
     onPickUp = { local, pointerInRoot, nodeInRoot, size ->
         val bandTop = band[0]?.takeIf { it.isAttached }?.positionInRoot()?.y

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -100,6 +100,7 @@ import de.jeanlucmakiola.calendula.ui.common.TimelineDragController
 import de.jeanlucmakiola.calendula.ui.common.TimelineDragOverlay
 import de.jeanlucmakiola.calendula.ui.common.TimelineDrop
 import de.jeanlucmakiola.calendula.ui.common.beginsOn
+import de.jeanlucmakiola.calendula.ui.common.eventDragAllowed
 import de.jeanlucmakiola.calendula.ui.common.eventMoveAction
 import de.jeanlucmakiola.calendula.ui.common.rememberEventDragSource
 import de.jeanlucmakiola.calendula.ui.common.rememberTimelineDragController
@@ -905,7 +906,7 @@ private fun EventBlock(
     val moveAction = eventMoveAction(block.event)
     // A block clipped at the top continues from the previous day: its top edge
     // is midnight, not the event's start, so dragging it would invent a time.
-    val draggable = moveAction != null && block.beginsOn(date, zone)
+    val draggable = eventDragAllowed(block.event) && block.beginsOn(date, zone)
     val dragModifier = rememberEventDragSource(
         enabled = draggable,
         key = block.event.instanceId,