Fix items not being movable when the next sort index wasn't plus or minus 1.

source/settings/settings.ts

@@ -68,19 +68,13 @@ export class Settings {
       throw new Error(`Failed to move item with ID: ${id}`);
     }
 
-    const previousIndex = targetItem.sortIndex;
-    let targetIndex = previousIndex;
-    if (direction === 'down') {
-      targetIndex += 1;
-    } else if (direction === 'up') {
-      targetIndex -= 1;
-    }
-
+    const currentIndex = targetItem.sortIndex;
+    const targetIndex = this.nextQueueItemSortIndex(currentIndex, direction);
     const existingItem = this.queue.find(
       (item) => item.sortIndex === targetIndex,
     );
-    if (existingItem !== undefined) {
-      existingItem.sortIndex = previousIndex;
+    if (existingItem !== undefined && targetIndex !== undefined) {
+      existingItem.sortIndex = currentIndex;
       targetItem.sortIndex = targetIndex;
       await this.save();
     }
@@ -95,6 +89,28 @@ export class Settings {
     return this.queue.sort((a, b) => a.sortIndex - b.sortIndex)[0];
   }
 
+  public nextQueueItemSortIndex(
+    currentIndex: number,
+    direction: Queue.MoveDirection,
+  ): number | undefined {
+    this.queue.sort((a, b) => {
+      return direction === 'up'
+        ? b.sortIndex - a.sortIndex
+        : a.sortIndex - b.sortIndex;
+    });
+
+    let foundCurrent = false;
+    for (const item of this.queue) {
+      if (foundCurrent) {
+        return item.sortIndex;
+      }
+
+      if (item.sortIndex === currentIndex) {
+        foundCurrent = true;
+      }
+    }
+  }
+
   public async removeQueueItem(id: number): Promise<void> {
     const itemIndex = this.queue.findIndex((item) => item.id === id);
     if (itemIndex === -1) {