fix(MemoryStorage): correctly respect the desc option (#1666)

packages/memory-storage/src/resource-clients/dataset.ts

@@ -132,7 +132,10 @@ export class DatasetClient<Data extends Dictionary = Dictionary> extends BaseCli
             this.throwOnNonExisting(StorageTypes.Dataset);
         }
 
-        const [start, end] = existingStoreById.getStartAndEndIndexes(offset, limit);
+        const [start, end] = existingStoreById.getStartAndEndIndexes(
+            desc ? Math.max(existingStoreById.itemCount - offset - limit, 0) : offset,
+            limit,
+        );
 
         const items: Data[] = [];
 

packages/memory-storage/test/reverse-datataset-list.test.ts

@@ -0,0 +1,55 @@
+import { rm } from 'node:fs/promises';
+import { resolve } from 'node:path';
+import { MemoryStorage } from '@crawlee/memory-storage';
+import type { DatasetClient } from '@crawlee/types';
+
+const elements = Array.from({ length: 10 }, (_, i) => ({ number: i }));
+
+describe('Dataset#listItems respects the desc option', () => {
+    const localDataDirectory = resolve(__dirname, './tmp/desc');
+    const storage = new MemoryStorage({
+        localDataDirectory,
+        persistStorage: false,
+    });
+
+    let dataset: DatasetClient;
+
+    afterAll(async () => {
+        await rm(localDataDirectory, { force: true, recursive: true });
+    });
+
+    beforeAll(async () => {
+        const { id: falseDatasetId } = await storage.datasets().getOrCreate('false');
+        dataset = storage.dataset(falseDatasetId);
+
+        await dataset.pushItems(elements);
+    });
+
+    test('with desc: false', async () => {
+        const result = await dataset.listItems({ desc: false, limit: 5 });
+
+        expect(result.items).toHaveLength(5);
+        expect(result.items).toStrictEqual(elements.slice(0, 5));
+    });
+
+    test('with desc: true', async () => {
+        const result = await dataset.listItems({ desc: true, limit: 5 });
+
+        expect(result.items).toHaveLength(5);
+        expect(result.items).toStrictEqual(elements.slice().reverse().slice(0, 5));
+    });
+
+    test('with desc: false and offset: 2', async () => {
+        const result = await dataset.listItems({ desc: false, limit: 5, offset: 2 });
+
+        expect(result.items).toHaveLength(5);
+        expect(result.items).toStrictEqual(elements.slice(2, 7));
+    });
+
+    test('with desc: true and offset: 2', async () => {
+        const result = await dataset.listItems({ desc: true, limit: 5, offset: 2 });
+
+        expect(result.items).toHaveLength(5);
+        expect(result.items).toStrictEqual(elements.slice().reverse().slice(2, 7));
+    });
+});