Enhance TrainingUnitSectionsEditor with improved section visibility logic

- Added logic to determine visibility of drop bands for sections in parallel phases, enhancing user experience during reordering.
- Updated the reorderBlocksImmutableWithPlanLoc function to better handle plan location adjustments based on section types and their positions.
- Improved handling of section indices for parallel streams, ensuring accurate representation of active streams and their corresponding sections.

frontend/src/components/TrainingUnitSectionsEditor.jsx

@@ -1173,8 +1173,28 @@ export default function TrainingUnitSectionsEditor({
           enableParallelPhaseControls &&
           pl?.phaseKind === 'parallel' &&
           (pl.parallelStreamOrderIndex ?? 0) !== activeParallelStream
+        const firstGlobalIdxThisPhase =
+          parallelPhaseOrder != null
+            ? firstSectionIndexByParallelPhase.get(parallelPhaseOrder)
+            : null
+        const firstVisibleIdxActiveStream =
+          parallelPhaseOrder != null && streamOrdersForParallelPhase.length
+            ? sectionIndicesForParallelStream(
+                list,
+                parallelPhaseOrder,
+                activeParallelStream
+              )[0]
+            : null
+        const hideDropBandBeforeOrphanFirstVisible =
+          parallelPhaseOrder != null &&
+          firstVisibleIdxActiveStream != null &&
+          sIdx === firstVisibleIdxActiveStream &&
+          firstGlobalIdxThisPhase != null &&
+          sIdx !== firstGlobalIdxThisPhase
+
         const showSectionDropBandBefore =
-          pl?.phaseKind !== 'parallel' || !hideParallelSection
+          (pl?.phaseKind !== 'parallel' || !hideParallelSection) &&
+          !hideDropBandBeforeOrphanFirstVisible
 
         const bandActiveBefore = (bx) =>
           enableSectionDragReorder &&

frontend/src/utils/trainingUnitSectionsForm.js

@@ -814,7 +814,19 @@ export function reorderBlocksImmutableWithPlanLoc(prev, fromI, toBeforeIdx) {
   const above = insertAt > 0 ? arr[insertAt - 1] : undefined
 
   let planLocNext = null
-  if (below?.planLoc?.phaseKind) {
+  const belowKind = below?.planLoc?.phaseKind
+  const aboveKind = above?.planLoc?.phaseKind
+
+  if (
+    belowKind === 'parallel' &&
+    (!above || aboveKind === 'whole_group')
+  ) {
+    if (aboveKind === 'whole_group') {
+      planLocNext = { ...above.planLoc }
+    } else {
+      planLocNext = defaultPlanLocWholeGroup(0)
+    }
+  } else if (belowKind) {
     planLocNext = { ...below.planLoc }
   } else if (insertAt === arr.length) {
     if (!above) {
@@ -875,7 +887,6 @@ export function reorderBlockIntoParallelStreamEnd(prev, fromI, phaseOrderIndex,
     insertAt = phaseIdx[phaseIdx.length - 1] + 1
   }
 
-  if (fromI < insertAt) insertAt -= 1
   insertAt = Math.max(0, Math.min(insertAt, arr.length))
   arr.splice(insertAt, 0, { ...moved, planLoc: { ...planLocTemplate } })
   return arr