Fix pagination (#11448)

Co-authored-by: Eric Bailey <git@esb.lol>

src/lib/api/feed/merge.test.ts

@@ -0,0 +1,106 @@
+import {type Client} from '@atproto/lex'
+
+import {app} from '#/lexicons'
+import {MergeFeedAPI} from './merge'
+
+const post = {} as app.bsky.feed.defs.FeedViewPost
+
+describe('MergeFeedAPI', () => {
+  it('drains a terminal following queue without restarting the source', async () => {
+    const api = new MergeFeedAPI({
+      client: {} as Client,
+      feedParams: {},
+      feedTuners: [],
+    })
+    api.reset()
+    api.following.queue = [post, post, post]
+    api.following.hasMore = false
+
+    const first = await api.fetch({cursor: 'started', limit: 2})
+    const second = await api.fetch({cursor: first.cursor, limit: 2})
+
+    expect(first.feed).toHaveLength(2)
+    expect(first.cursor).toBeDefined()
+    expect(second.feed).toHaveLength(1)
+    expect(second.cursor).toBeUndefined()
+  })
+
+  it('stops when the following source repeats its cursor', async () => {
+    const call = jest
+      .fn()
+      .mockResolvedValueOnce({feed: [], cursor: 'a'})
+      .mockResolvedValueOnce({feed: [], cursor: 'a'})
+    const api = new MergeFeedAPI({
+      client: {call} as unknown as Client,
+      feedParams: {},
+      feedTuners: [],
+    })
+
+    const first = await api.fetch({cursor: undefined, limit: 1})
+    const second = await api.fetch({cursor: first.cursor, limit: 1})
+
+    expect(first.cursor).toBeDefined()
+    expect(second.cursor).toBeUndefined()
+    expect(call).toHaveBeenCalledTimes(2)
+  })
+
+  it('stops when the following source returns an empty cursor', async () => {
+    const call = jest.fn().mockResolvedValue({feed: [], cursor: ''})
+    const api = new MergeFeedAPI({
+      client: {call} as unknown as Client,
+      feedParams: {},
+      feedTuners: [],
+    })
+
+    const result = await api.fetch({cursor: undefined, limit: 1})
+
+    expect(result.cursor).toBeUndefined()
+    expect(call).toHaveBeenCalledTimes(1)
+  })
+
+  it('stops when the following source cycles to an earlier cursor', async () => {
+    const call = jest
+      .fn()
+      .mockResolvedValueOnce({feed: [], cursor: 'a'})
+      .mockResolvedValueOnce({feed: [], cursor: 'b'})
+      .mockResolvedValueOnce({feed: [], cursor: 'a'})
+    const api = new MergeFeedAPI({
+      client: {call} as unknown as Client,
+      feedParams: {},
+      feedTuners: [],
+    })
+
+    const first = await api.fetch({cursor: undefined, limit: 1})
+    const second = await api.fetch({cursor: first.cursor, limit: 1})
+    const third = await api.fetch({cursor: second.cursor, limit: 1})
+
+    expect(third.cursor).toBeUndefined()
+    expect(call).toHaveBeenCalledTimes(3)
+  })
+
+  it('drains a terminal custom-feed queue without restarting the source', async () => {
+    const call = jest.fn()
+    const api = new MergeFeedAPI({
+      client: {call} as unknown as Client,
+      feedParams: {
+        mergeFeedEnabled: true,
+        mergeFeedSources: [
+          'at://did:example:feed/app.bsky.feed.generator/test',
+        ],
+      },
+      feedTuners: [],
+    })
+    api.reset()
+    api.following.hasMore = false
+    api.customFeeds[0].queue = [post, post, post]
+    api.customFeeds[0].hasMore = false
+
+    const first = await api.fetch({cursor: 'started', limit: 2})
+    const second = await api.fetch({cursor: first.cursor, limit: 2})
+
+    expect(first.feed).toHaveLength(2)
+    expect(second.feed).toHaveLength(1)
+    expect(second.cursor).toBeUndefined()
+    expect(call).not.toHaveBeenCalled()
+  })
+})