From 556ec2ecf00dae11a486a75b860c860fa9766ef9 Mon Sep 17 00:00:00 2001
From: Calvin Liang <me@calvin.sh>
Date: Thu, 12 Dec 2024 01:24:08 -0800
Subject: [PATCH] fix #57

---
 .../reorderable/ReorderableLazyCollection.kt  | 31 +++++++++++++------
 .../kotlin/sh/calvin/reorderable/util.kt      |  6 ++++
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/ReorderableLazyCollection.kt b/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/ReorderableLazyCollection.kt
index 1e29d5a..f3eb127 100644
--- a/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/ReorderableLazyCollection.kt
+++ b/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/ReorderableLazyCollection.kt
@@ -511,26 +511,39 @@ open class ReorderableLazyCollectionState<out T> internal constructor(
             .reverseAxisWithLayoutDirectionIfLazyVerticalStaggeredGridRtlFix()
         val startOffset = draggingItem.offset.toOffset() + dragOffset
         val endOffset = startOffset + draggingItem.size.toSize()
-        val draggingItemRect = Rect(startOffset, endOffset).maxOutAxis(orientation)
+        val draggingItemRect = Rect(startOffset, endOffset).maxOutAxis(orientation.opposite)
+        val itemsInContentArea = state.layoutInfo.getItemsInContentArea(scrollThresholdPadding)
+            // if we can't find an item in the content area but still need to move the dragging item
+            // we will need to search outside the content area
+            .ifEmpty { state.layoutInfo.visibleItemsInfo }
         val targetItem = findTargetItem(
             draggingItemRect,
-            items = state.layoutInfo.getItemsInContentArea(scrollThresholdPadding),
+            items = itemsInContentArea,
             direction.opposite,
-        ) ?: state.layoutInfo.getItemsInContentArea(
-            scrollThresholdPadding
-        ).let {
+        ) ?: itemsInContentArea.let {
             val targetItemFunc = { item: LazyCollectionItemInfo<T> ->
-                item.key in reorderableKeys && item.index != state.firstVisibleItemIndex
+                item.key in reorderableKeys
             }
             when (direction) {
                 Scroller.Direction.FORWARD -> it.findLast(targetItemFunc)
                 Scroller.Direction.BACKWARD -> it.find(targetItemFunc)
             }
         }
+        if (targetItem == null) {
+            onMoveStateMutex.unlock()
+            return
+        }
+        // this solves https://github.com/Calvin-LL/Reorderable/issues/57
+        val isTargetDirectionCorrect = when (direction) {
+            Scroller.Direction.FORWARD -> targetItem.index > draggingItem.index
+            Scroller.Direction.BACKWARD -> targetItem.index < draggingItem.index
+        }
+        if (!isTargetDirectionCorrect) {
+            onMoveStateMutex.unlock()
+            return
+        }
         val job = scope.launch {
-            if (targetItem != null) {
-                moveItems(draggingItem, targetItem)
-            }
+            moveItems(draggingItem, targetItem)
         }
         onMoveStateMutex.unlock()
         job.join()
diff --git a/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/util.kt b/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/util.kt
index df945a9..6aa3676 100644
--- a/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/util.kt
+++ b/reorderable/src/commonMain/kotlin/sh/calvin/reorderable/util.kt
@@ -7,6 +7,12 @@ import androidx.compose.ui.unit.IntOffset
 import androidx.compose.ui.unit.IntSize
 import kotlinx.coroutines.sync.Mutex
 
+internal val Orientation.opposite
+    get() = when (this) {
+        Orientation.Vertical -> Orientation.Horizontal
+        Orientation.Horizontal -> Orientation.Vertical
+    }
+
 internal fun Offset.getAxis(orientation: Orientation) = when (orientation) {
     Orientation.Vertical -> y
     Orientation.Horizontal -> x