Hold a timeline resize in one ResizeSession

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

@@ -626,25 +626,8 @@ class TimelineDragController {
      */
     private var originSlot: Triple<LocalDate, Int, Int>? = null
 
-    /** The edge a resize is dragging, or null for a plain drag (#141). */
-    private var resizeEdge: ResizeEdge? = null
-
-    /** The day the resized event starts on; its edges are minutes from that midnight. */
-    private var resizeDay: LocalDate? = null
-    private var resizeStartMin = 0
-    private var resizeEndMin = 0
-
-    /** How far the finger sits past the edge it grabbed, so the edge doesn't jump to it. */
-    private var resizeGrabMin = 0f
-
-    /** The column the resized edge is in, held until the finger is well into another. */
-    private var resizeColumn: Int? = null
-
-    /** The slot the resized edge sits on, held against a finger trembling between two. */
-    private var resizeSlot: Int? = null
-
-    /** The day, counted from the event's start day, the finger is resizing in. */
-    private var resizeEdgeDay = 0
+    /** The resize in progress, or null for a plain drag (#141). */
+    private var resize: ResizeSession? = null
 
     fun begin(
         block: TimedBlock,
@@ -691,10 +674,7 @@ class TimelineDragController {
     }
 
     fun cancel() {
-        resizeEdge = null
-        resizeDay = null
-        resizeColumn = null
-        resizeSlot = null
+        resize = null
         source = null
         clipOffsetMin = 0
         dragZone = null
@@ -800,11 +780,9 @@ class TimelineDragController {
         pointerInRoot: Offset,
     ) {
         val span = wallClockSpan(block.event, zone)
+        val session = ResizeSession(edge, span.day, span.startMin, span.endMin)
         source = block
-        resizeEdge = edge
-        resizeDay = span.day
-        resizeStartMin = span.startMin
-        resizeEndMin = span.endMin
+        resize = session
         clipOffsetMin = 0
         this.titleLines = titleLines
         settling = null
@@ -813,12 +791,12 @@ class TimelineDragController {
         liftedInstanceId = block.event.instanceId
         pointer = pointerInRoot
         // Measured from the edge's own column: the handle overhangs into the next.
-        val edgeDay = if (edge == ResizeEdge.Top) 0 else (resizeEndMin - 1).floorDiv(MINUTES_PER_DAY).coerceAtLeast(0)
+        val edgeDay = if (edge == ResizeEdge.Top) 0 else (session.endMin - 1).floorDiv(MINUTES_PER_DAY).coerceAtLeast(0)
         val edgeIndex = geometry.days.indexOf(span.day.plus(edgeDay, DateTimeUnit.DAY))
-        resizeColumn = edgeIndex.takeIf { it >= 0 }
+        session.column = edgeIndex.takeIf { it >= 0 }
             ?.let { column(it) }
-        resizeGrabMin = (pointerResizeMinutes() ?: 0f) -
-            if (edge == ResizeEdge.Top) resizeStartMin else resizeEndMin
+        session.grabMin = (pointerResizeMinutes(session) ?: 0f) -
+            if (edge == ResizeEdge.Top) session.startMin else session.endMin
         originSlot = null
         recompute()
         originSlot = drag?.slot
@@ -834,7 +812,7 @@ class TimelineDragController {
     fun preview(zone: TimeZone): EventInstance? {
         val (date, startMin, spanMin) = landingSlot?.takeIf { it != originSlot } ?: return null
         val event = source?.event ?: return null
-        val edge = resizeEdge
+        val edge = resize?.edge
         if (edge != null) {
             val drop = resizedDrop(event, edge, date, startMin, spanMin, zone)
             return event.copy(start = drop.start, end = drop.end)
@@ -850,7 +828,7 @@ class TimelineDragController {
     fun finishResize(zone: TimeZone): TimelineResizeDrop? {
         val landed = drag
         val origin = originSlot
-        val edge = resizeEdge
+        val edge = resize?.edge
         cancel()
         if (landed == null || landed.slot == origin) return null
         val drop = resizedDrop(landed.event, edge, landed.date, landed.eventStartMin, landed.eventSpanMin, zone)
@@ -862,9 +840,8 @@ class TimelineDragController {
      * Where the finger is, in minutes from the resized event's start day —
      * past 1440 in a later column, negative in an earlier one.
      */
-    private fun pointerResizeMinutes(): Float? {
+    private fun pointerResizeMinutes(session: ResizeSession): Float? {
         val grid = geometry.grid?.takeIf { it.isAttached } ?: return null
-        val day = resizeDay ?: return null
         val hourPx = geometry.hourPx
         val columnPx = geometry.columnWidthPx
         val days = geometry.days
@@ -872,22 +849,23 @@ class TimelineDragController {
         val origin = grid.positionInRoot()
         val held = stickyColumn(
             position = (pointer.x - origin.x) / columnPx,
-            held = resizeColumn,
+            held = session.column,
             lastIndex = days.lastIndex,
         )
-        resizeColumn = held
-        val dayOffset = (days[column(held)].toEpochDays() - day.toEpochDays()).toInt()
-        resizeEdgeDay = dayOffset
+        session.column = held
+        val dayOffset = (days[column(held)].toEpochDays() - session.day.toEpochDays()).toInt()
+        session.edgeDay = dayOffset
         return dayOffset * MINUTES_PER_DAY + (pointer.y - origin.y) / hourPx * 60f
     }
 
-    private fun recomputeResize(edge: ResizeEdge) {
+    private fun recomputeResize(session: ResizeSession) {
         val block = source ?: return
-        val day = resizeDay ?: return
-        val raw = pointerResizeMinutes() ?: return
-        val slot = stickySnap(raw - resizeGrabMin, resizeSlot)
-        resizeSlot = slot
-        val (start, end) = resizedSpan(edge, resizeStartMin, resizeEndMin, slot.toFloat(), resizeEdgeDay)
+        val edge = session.edge
+        val day = session.day
+        val raw = pointerResizeMinutes(session) ?: return
+        val slot = stickySnap(raw - session.grabMin, session.slot)
+        session.slot = slot
+        val (start, end) = resizedSpan(edge, session.startMin, session.endMin, slot.toFloat(), session.edgeDay)
         val days = geometry.days
         val origin = geometry.grid?.takeIf { it.isAttached }?.positionInRoot() ?: return
         // Which column the start day sits in, possibly off either end of the view.
@@ -946,7 +924,7 @@ class TimelineDragController {
      * no move events while auto-scroll walks the content underneath it.
      */
     fun recompute() {
-        resizeEdge?.let {
+        resize?.let {
             recomputeResize(it)
             return
         }
@@ -1049,6 +1027,27 @@ class TimelineDragController {
     }
 }
 
+/** One resize gesture (#141): the edge it drags, and the edges as minutes from [day]'s midnight. */
+private class ResizeSession(
+    val edge: ResizeEdge,
+    /** The day the resized event starts on. */
+    val day: LocalDate,
+    val startMin: Int,
+    val endMin: Int,
+) {
+    /** How far the finger sits past the edge it grabbed, so the edge doesn't jump to it. */
+    var grabMin = 0f
+
+    /** The column the resized edge is in, held until the finger is well into another. */
+    var column: Int? = null
+
+    /** The slot the resized edge sits on, held against a finger trembling between two. */
+    var slot: Int? = null
+
+    /** The day, counted from the event's start day, the finger is resizing in. */
+    var edgeDay = 0
+}
+
 @Composable
 fun rememberTimelineDragController(): TimelineDragController {
     val controller = remember { TimelineDragController() }