From 4139c9e8c4fe9f136c21b80e4127ac0c851cbdca Mon Sep 17 00:00:00 2001
From: Tobias Jordan <mail@tobiasjordan.com>
Date: Thu, 2 Jun 2022 00:43:32 +0200
Subject: [PATCH] Fix batch moving of rows in NSTableView

`NSTableView` doesn't support batch updating so every change (insert, delete, move) may alter its row indexes, making it difficult to apply moves generated from a `StagedChangeset` unless indexes are corrected accordingly and it is ensured that inserts are always performed after any moves.
---
 Sources/Extensions/AppKitExtension.swift | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/Sources/Extensions/AppKitExtension.swift b/Sources/Extensions/AppKitExtension.swift
index 8616187..0570448 100644
--- a/Sources/Extensions/AppKitExtension.swift
+++ b/Sources/Extensions/AppKitExtension.swift
@@ -73,16 +73,24 @@ public extension NSTableView {
                 removeRows(at: IndexSet(changeset.elementDeleted.map { $0.element }), withAnimation: deleteRowsAnimation())
             }
 
-            if !changeset.elementInserted.isEmpty {
-                insertRows(at: IndexSet(changeset.elementInserted.map { $0.element }), withAnimation: insertRowsAnimation())
-            }
-
             if !changeset.elementUpdated.isEmpty {
                 reloadData(forRowIndexes: IndexSet(changeset.elementUpdated.map { $0.element }), columnIndexes: IndexSet(0..<tableColumns.count))
             }
 
-            for (source, target) in changeset.elementMoved {
-                moveRow(at: source.element, to: target.element)
+            if !changeset.elementMoved.isEmpty {
+                let insertionIndices = IndexSet(changeset.elementInserted.map { $0.element })
+                var movedSourceIndices = IndexSet()
+
+                for (source, target) in changeset.elementMoved {
+                    let sourceElementOffset = movedSourceIndices.count(in: source.element...)
+                    let targetElementOffset = insertionIndices.count(in: 0..<target.element)
+                    moveRow(at: source.element + sourceElementOffset, to: target.element - targetElementOffset)
+                    movedSourceIndices.insert(source.element)
+                }
+            }
+
+            if !changeset.elementInserted.isEmpty {
+                insertRows(at: IndexSet(changeset.elementInserted.map { $0.element }), withAnimation: insertRowsAnimation())
             }
 
             endUpdates()