fix: Prevent broken/strange checklist reordering

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Fixed inconsistent checklist sorting when the "Move checked items to the bottom" option is enabled ([#59])
+
 ## [1.6.0] - 2025-10-29
 ### Changed
 - Compatibility updates for Android 15 & 16
@@ -91,6 +94,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Initial release
 
+[#59]: https://github.com/FossifyOrg/Notes/issues/59
 [#81]: https://github.com/FossifyOrg/Notes/issues/81
 [#83]: https://github.com/FossifyOrg/Notes/issues/83
 [#99]: https://github.com/FossifyOrg/Notes/issues/99

app/src/main/kotlin/org/fossify/notes/fragments/TasksFragment.kt

@@ -288,13 +288,28 @@ class TasksFragment : NoteFragment(), TasksActionListener {
 
     override fun moveTask(fromPosition: Int, toPosition: Int) {
         switchToCustomSorting()
+
+        val sortableIndices = mutableListOf<Int>()
+        val checkedCanBeMoved = config?.moveDoneChecklistItems == false
+        for (i in 0 until tasks.size) {
+            if (checkedCanBeMoved || !tasks[i].isDone) {
+                sortableIndices.add(i)
+            }
+        }
+
         if (fromPosition < toPosition) {
             for (i in fromPosition until toPosition) {
-                tasks.swap(i, i + 1)
+                val toMoveIndex = sortableIndices[i]
+                if (i + 1 < sortableIndices.size) {
+                    val headingIndex = sortableIndices[i + 1]
+                    tasks.swap(toMoveIndex, headingIndex)
+                }
             }
         } else {
             for (i in fromPosition downTo toPosition + 1) {
-                tasks.swap(i, i - 1)
+                val toMoveIndex = sortableIndices[i]
+                val headingIndex = sortableIndices[i - 1]
+                tasks.swap(toMoveIndex, headingIndex)
             }
         }