import { afterEach, describe, expect, it, vi } from 'vitest';
import { collectRecentSince } from 'docmost-client';

/**
 * Unit tests for the pure cursor-pagination helper behind listRecentSince.
 * `fetchPage` is faked (no network); each test models a different server
 * behaviour to exercise one stop condition.
 */

type Item = { id: string; updatedAt: string };

/**
 * Build a fake `fetchPage` from a list of pages. Each page is served in order;
 * the nextCursor of page i points at page i+1 (the last page has no cursor).
 * The handed-back cursor is asserted to match what we previously emitted so a
 * caller that mis-threads the cursor would fail loudly. Tracks the call count.
 */
function fakeServer(pages: Item[][]) {
  let calls = 0;
  const cursorFor = (i: number) => (i < pages.length - 1 ? `c${i}` : null);
  const fetchPage = async (cursor: string | null) => {
    // Resolve which page this cursor selects: null -> page 0, "cN" -> page N+1.
    const idx = cursor === null ? 0 : Number(cursor.slice(1)) + 1;
    calls++;
    const items = pages[idx] ?? [];
    return { items, nextCursor: cursorFor(idx) };
  };
  return {
    fetchPage,
    get calls() {
      return calls;
    },
  };
}

afterEach(() => {
  vi.restoreAllMocks();
});

describe('collectRecentSince', () => {
  it('stops at the cutoff page and does not fetch beyond it', async () => {
    // Page 0: all newer than the cutoff. Page 1: contains the cutoff item, so
    // the walk must stop here and never request page 2.
    const server = fakeServer([
      [
        { id: 'a', updatedAt: '2026-06-16T10:00:00Z' },
        { id: 'b', updatedAt: '2026-06-16T09:00:00Z' },
      ],
      [
        { id: 'c', updatedAt: '2026-06-16T08:00:00Z' },
        { id: 'd', updatedAt: '2026-06-16T05:00:00Z' }, // <= cutoff -> stop
        { id: 'e', updatedAt: '2026-06-16T04:00:00Z' },
      ],
      [{ id: 'f', updatedAt: '2026-06-16T03:00:00Z' }], // must NOT be fetched
    ]);

    const out = await collectRecentSince(
      server.fetchPage,
      '2026-06-16T05:00:00Z',
    );

    // Only strictly-newer items, in server order; the cutoff item 'd' and
    // everything after it is excluded.
    expect(out.map((i) => i.id)).toEqual(['a', 'b', 'c']);
    // Fetched page 0 and page 1 only — stopped at the cutoff page.
    expect(server.calls).toBe(2);
  });

  it('dedups ids that overlap across pages', async () => {
    // The cursor advances, but page boundaries overlap: 'b' appears on both
    // pages. The dedup-by-id Set must keep it exactly once.
    const server = fakeServer([
      [
        { id: 'a', updatedAt: '2026-06-16T10:00:00Z' },
        { id: 'b', updatedAt: '2026-06-16T09:00:00Z' },
      ],
      [
        { id: 'b', updatedAt: '2026-06-16T09:00:00Z' }, // overlap
        { id: 'c', updatedAt: '2026-06-16T08:00:00Z' },
      ],
    ]);

    const out = await collectRecentSince(
      server.fetchPage,
      '2026-06-16T01:00:00Z',
    );

    expect(out.map((i) => i.id)).toEqual(['a', 'b', 'c']);
  });

  it('terminates when the server ignores the cursor (zero new items)', async () => {
    // A broken server that returns the SAME first page on every call and always
    // claims a nextCursor. Without the zero-new-items guard this loops to the
    // cap; with it, the second fetch contributes nothing and the walk stops.
    let calls = 0;
    const fetchPage = async (_cursor: string | null) => {
      calls++;
      return {
        items: [
          { id: 'a', updatedAt: '2026-06-16T10:00:00Z' },
          { id: 'b', updatedAt: '2026-06-16T09:00:00Z' },
        ] as Item[],
        nextCursor: 'always', // server always claims another page
      };
    };

    const out = await collectRecentSince(fetchPage, '2026-06-16T01:00:00Z');

    // The newer items are returned exactly once (no hang, no duplicates).
    expect(out.map((i) => i.id)).toEqual(['a', 'b']);
    // First page collects, second page is all-seen -> stop. Capped well below
    // the default hardPageCap, proving the loop terminated.
    expect(calls).toBe(2);
  });

  it('returns only the first page when sinceIso is null', async () => {
    const server = fakeServer([
      [
        { id: 'a', updatedAt: '2026-06-16T10:00:00Z' },
        { id: 'b', updatedAt: '2026-06-16T09:00:00Z' },
      ],
      [{ id: 'c', updatedAt: '2026-06-16T08:00:00Z' }],
    ]);

    const out = await collectRecentSince(server.fetchPage, null);

    expect(out.map((i) => i.id)).toEqual(['a', 'b']);
    // Exactly one page fetched.
    expect(server.calls).toBe(1);
  });

  it('stops at hardPageCap and warns when results may be truncated', async () => {
    // Every page is all-newer-than-cutoff, every item is unique, and there is
    // always a nextCursor: the only thing that can stop the walk is the cap.
    let n = 0;
    const fetchPage = async (_cursor: string | null) => {
      const id = `id${n++}`;
      return {
        items: [{ id, updatedAt: '2026-06-16T10:00:00Z' }] as Item[],
        nextCursor: 'next', // never runs out
      };
    };

    const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});

    const cap = 5;
    const out = await collectRecentSince(
      fetchPage,
      '2020-01-01T00:00:00Z',
      cap,
    );

    // Exactly `cap` pages were collected (one unique item each).
    expect(out).toHaveLength(cap);
    expect(warn).toHaveBeenCalledTimes(1);
    expect(String(warn.mock.calls[0][0])).toContain('hardPageCap=5');
  });

  it('preserves server (descending) order across pages', async () => {
    const server = fakeServer([
      [
        { id: 'a', updatedAt: '2026-06-16T10:00:00Z' },
        { id: 'b', updatedAt: '2026-06-16T09:00:00Z' },
      ],
      [
        { id: 'c', updatedAt: '2026-06-16T08:00:00Z' },
        { id: 'd', updatedAt: '2026-06-16T07:00:00Z' },
      ],
    ]);

    const out = await collectRecentSince(
      server.fetchPage,
      '2026-06-16T01:00:00Z',
    );

    expect(out.map((i) => i.id)).toEqual(['a', 'b', 'c', 'd']);
  });
});