Share the drag controller's piece building, settling, column flip and slot snap

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

@@ -390,17 +390,20 @@ internal fun resizedSpan(
         }
         if (wrongWay) return startMin to endMin
     }
-    val snapped = (edgeMin / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
+    val snapped = snapToSlot(edgeMin)
     return when (edge) {
         ResizeEdge.Top -> minOf(snapped, endMin - DRAG_SNAP_MINUTES) to endMin
         ResizeEdge.Bottom -> startMin to maxOf(snapped, startMin + DRAG_SNAP_MINUTES)
     }
 }
 
+/** [minutes] rounded to the nearest [DRAG_SNAP_MINUTES] slot. */
+internal fun snapToSlot(minutes: Float): Int = (minutes / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
+
 /** [minutes] snapped, kept at [held] until three quarters of a step away. */
 internal fun stickySnap(minutes: Float, held: Int?): Int {
     if (held != null && kotlin.math.abs(minutes - held) < DRAG_SNAP_MINUTES * 0.75f) return held
-    return (minutes / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
+    return snapToSlot(minutes)
 }
 
 /** How far past its column's side the finger has to go before a resize changes day. */
@@ -766,6 +769,12 @@ class TimelineDragController {
         if (landed == null || landed.slot == origin) return null
         // A draft dropped on a day off screen would vanish, so it stays where it was (#153).
         if (landed.edgeOnly && landed.event.isDraft) return null
+        settle(landed)
+        return TimelineDrop(landed.event, landed.date, landed.startMin, clipOffset)
+    }
+
+    /** Keep [landed]'s copy on the target as [settling] until [release]; [end] is a resize's. */
+    private fun settle(landed: TimelineDrag, end: Instant? = null) {
         settlingSelected = selection?.event?.instanceId == landed.event.instanceId
         // An edge piece is a hint for the finger, not a preview of the landing
         // slot: the event belongs to a day this timeline has no column for, so
@@ -775,8 +784,8 @@ class TimelineDragController {
         liftedInstanceId = landed.event.instanceId
         settledOrigin = landed.event.eventId to landed.event.start
         settledAbandonedMark = abandonedTicks?.value ?: 0
+        settledEnd = end
         drops++
-        return TimelineDrop(landed.event, landed.date, landed.startMin, clipOffset)
     }
 
     /**
@@ -807,7 +816,7 @@ class TimelineDragController {
         val edgeDay = if (edge == ResizeEdge.Top) 0 else (resizeEndMin - 1).floorDiv(MINUTES_PER_DAY).coerceAtLeast(0)
         val edgeIndex = geometry.days.indexOf(span.day.plus(edgeDay, DateTimeUnit.DAY))
         resizeColumn = edgeIndex.takeIf { it >= 0 }
-            ?.let { if (geometry.isRtl) geometry.days.lastIndex - it else it }
+            ?.let { column(it) }
         resizeGrabMin = (pointerResizeMinutes() ?: 0f) -
             if (edge == ResizeEdge.Top) resizeStartMin else resizeEndMin
         originSlot = null
@@ -845,13 +854,7 @@ class TimelineDragController {
         cancel()
         if (landed == null || landed.slot == origin) return null
         val drop = resizedDrop(landed.event, edge, landed.date, landed.eventStartMin, landed.eventSpanMin, zone)
-        settlingSelected = selection?.event?.instanceId == landed.event.instanceId
+        settle(landed, end = drop.end)
-        settling = if (landed.edgeOnly) landed.copy(pieces = emptyList()) else landed
-        liftedInstanceId = landed.event.instanceId
-        settledOrigin = landed.event.eventId to landed.event.start
-        settledAbandonedMark = abandonedTicks?.value ?: 0
-        settledEnd = drop.end
-        drops++
         return drop
     }
 
@@ -867,14 +870,13 @@ class TimelineDragController {
         val days = geometry.days
         if (hourPx <= 0f || columnPx <= 0f || days.isEmpty()) return null
         val origin = grid.positionInRoot()
-        val column = stickyColumn(
+        val held = stickyColumn(
             position = (pointer.x - origin.x) / columnPx,
             held = resizeColumn,
             lastIndex = days.lastIndex,
         )
-        resizeColumn = column
+        resizeColumn = held
-        val dayIndex = if (geometry.isRtl) days.lastIndex - column else column
+        val dayOffset = (days[column(held)].toEpochDays() - day.toEpochDays()).toInt()
-        val dayOffset = (days[dayIndex].toEpochDays() - day.toEpochDays()).toInt()
         resizeEdgeDay = dayOffset
         return dayOffset * MINUTES_PER_DAY + (pointer.y - origin.y) / hourPx * 60f
     }
@@ -887,8 +889,6 @@ class TimelineDragController {
         resizeSlot = slot
         val (start, end) = resizedSpan(edge, resizeStartMin, resizeEndMin, slot.toFloat(), resizeEdgeDay)
         val days = geometry.days
-        val hourPx = geometry.hourPx
-        val columnPx = geometry.columnWidthPx
         val origin = geometry.grid?.takeIf { it.isAttached }?.positionInRoot() ?: return
         // Which column the start day sits in, possibly off either end of the view.
         val startIndex = (day.toEpochDays() - days.first().toEpochDays()).toInt()
@@ -901,20 +901,7 @@ class TimelineDragController {
             eventStartMin = start,
             eventSpanMin = end - start,
             titleLines = titleLines,
-            pieces = slices.map { slice ->
+            pieces = pieces(slices, startIndex, origin),
-                val dayIndex = startIndex + slice.dayOffset
-                val col = if (geometry.isRtl) days.lastIndex - dayIndex else dayIndex
-                val bounds = dragPieceBounds(slice, hourPx, geometry.blockInsetPx)
-                TimelineDragPiece(
-                    topLeftInRoot = Offset(x = origin.x + col * columnPx, y = origin.y + bounds.top),
-                    sizePx = IntSize(
-                        (columnPx - geometry.columnGapPx).roundToInt(),
-                        bounds.height.roundToInt(),
-                    ),
-                    continuesBefore = slice.continuesBefore,
-                    continuesAfter = slice.continuesAfter,
-                )
-            },
             edgeOnly = slices.isEmpty(),
             markerMin = if (edge == ResizeEdge.Top) {
                 start.mod(MINUTES_PER_DAY)
@@ -972,10 +959,9 @@ class TimelineDragController {
 
         val origin = grid.positionInRoot()
         val rawMinutes = (pointer.y - grab.y - origin.y) / hourPx * 60f
-        val snapped = (rawMinutes / DRAG_SNAP_MINUTES).roundToInt() * DRAG_SNAP_MINUTES
+        val snapped = snapToSlot(rawMinutes)
         val zone = dragZone ?: return
-        val column = ((pointer.x - origin.x) / columnPx).toInt().coerceIn(0, days.lastIndex)
+        val dayIndex = column(((pointer.x - origin.x) / columnPx).toInt().coerceIn(0, days.lastIndex))
-        val dayIndex = if (geometry.isRtl) days.lastIndex - column else column
         val target = days[dayIndex]
         val keep = dragKept
         // Measured where it would land: the drop keeps the real duration, which in
@@ -1003,14 +989,19 @@ class TimelineDragController {
             titleLines = titleLines,
             // Bounded to the columns this timeline actually shows: a day it
             // doesn't has no piece to draw. The write is unaffected.
-            pieces = slices
+            pieces = pieces(slices, dayIndex, origin),
-                .map { slice ->
+            edgeOnly = onGrid.isEmpty(),
-                    val day = dayIndex + slice.dayOffset
+        )
-                    val col = if (geometry.isRtl) days.lastIndex - day else day
+    }
-                    val bounds = dragPieceBounds(slice, hourPx, geometry.blockInsetPx)
+
+    /** [slices] as floating pieces, the first slice's day being [dayIndex] in the shown days. */
+    private fun pieces(slices: List<DragSlice>, dayIndex: Int, origin: Offset): List<TimelineDragPiece> {
+        val columnPx = geometry.columnWidthPx
+        return slices.map { slice ->
+            val bounds = dragPieceBounds(slice, geometry.hourPx, geometry.blockInsetPx)
             TimelineDragPiece(
                 topLeftInRoot = Offset(
-                            x = origin.x + col * columnPx,
+                    x = origin.x + column(dayIndex + slice.dayOffset) * columnPx,
                     y = origin.y + bounds.top,
                 ),
                 sizePx = IntSize(
@@ -1020,10 +1011,11 @@ class TimelineDragController {
                 continuesBefore = slice.continuesBefore,
                 continuesAfter = slice.continuesAfter,
             )
-                },
-            edgeOnly = onGrid.isEmpty(),
-        )
         }
+    }
+
+    /** The on-screen column of a day index, and back: right-to-left lays the days out mirrored. */
+    private fun column(index: Int): Int = if (geometry.isRtl) geometry.days.lastIndex - index else index
 
     /**
      * Hold the scroll for the whole drag and nudge it once per frame while the