add function diffArraysSimple for more efficient change detection

packages/backend/test/unit/misc/diff-arrays.ts

@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { diffArrays } from '@/misc/diff-arrays.js';
+import { diffArrays, diffArraysSimple } from '@/misc/diff-arrays.js';
 
 describe(diffArrays, () => {
 	it('should return empty result when both inputs are null', () => {
@@ -51,3 +51,41 @@ describe(diffArrays, () => {
 		expect(result.removed).toEqual(['b', 'd']);
 	});
 });
+
+describe(diffArraysSimple, () => {
+	it('should return false when both inputs are null', () => {
+		const result = diffArraysSimple(null, null);
+		expect(result).toBe(false);
+	});
+
+	it('should return false when both inputs are empty', () => {
+		const result = diffArraysSimple([], []);
+		expect(result).toBe(false);
+	});
+
+	it('should return true when before is populated and after is empty', () => {
+		const result = diffArraysSimple([1, 2, 3], []);
+		expect(result).toBe(true);
+	});
+
+	it('should return true when before is empty and after is populated', () => {
+		const result = diffArraysSimple([], [1, 2, 3]);
+		expect(result).toBe(true);
+	});
+
+	it('should return true when values have changed', () => {
+		const result = diffArraysSimple(
+			['a', 'a', 'b', 'c'],
+			['a', 'b', 'c', 'd'],
+		);
+		expect(result).toBe(true);
+	});
+
+	it('should return false when values have not changed', () => {
+		const result = diffArraysSimple(
+			['a', 'a', 'b', 'c'],
+			['a', 'b', 'c', 'c'],
+		);
+		expect(result).toBe(false);
+	});
+});