import { describe, expect, it } from 'bun:test';
import { queryAcross } from './mail-scope';

// The merge is the part that can be silently wrong: a page with a hole in it looks like missing mail rather
// than like a bug. These pin the property that makes it exact — each mailbox is asked for offset+limit.
const mailbox = (dates: string[]) =>
  ({
    account: { id: dates.length, email: `a${dates.length}@x` },
    db: {} as never,
  }) as never;

describe('queryAcross', () => {
  const A = ['2026-08-10', '2026-08-08', '2026-08-02'];
  const B = ['2026-08-09', '2026-08-07', '2026-08-01'];

  const opened = [
    { account: { id: 1, email: 'a@x' }, db: 'A' },
    { account: { id: 2, email: 'b@x' }, db: 'B' },
  ] as never as Parameters<typeof queryAcross>[0];

  const run = (db: unknown, take: number) =>
    ((db as unknown as string) === 'A' ? A : B).slice(0, take).map((date) => ({ date }));

  it('interleaves newest-first across mailboxes', () => {
    const rows = queryAcross(opened, run as never, { sortBy: (r) => String(r.date), limit: 4, offset: 0 });
    expect(rows.map((r) => r.date)).toEqual(['2026-08-10', '2026-08-09', '2026-08-08', '2026-08-07']);
  });

  it('labels every row with the mailbox it came from', () => {
    const rows = queryAcross(opened, run as never, { sortBy: (r) => String(r.date), limit: 2, offset: 0 });
    expect(rows.map((r) => r.accountEmail)).toEqual(['a@x', 'b@x']);
  });

  // The reason each mailbox is asked for offset+limit rather than limit: page 2 must not skip a row that
  // ranked low locally and high globally.
  it('pages without a hole', () => {
    const p1 = queryAcross(opened, run as never, { sortBy: (r) => String(r.date), limit: 2, offset: 0 });
    const p2 = queryAcross(opened, run as never, { sortBy: (r) => String(r.date), limit: 2, offset: 2 });
    const p3 = queryAcross(opened, run as never, { sortBy: (r) => String(r.date), limit: 2, offset: 4 });
    expect([...p1, ...p2, ...p3].map((r) => r.date)).toEqual([...A, ...B].sort().reverse());
  });

  // The contract, pinned: local order must match merge order. A mailbox handing back rows in the wrong
  // direction breaks top-K silently, which is why the `descending` option was removed rather than fixed —
  // it flipped the merge while every caller's SQL still said ORDER BY date DESC.
  it('trusts each mailbox to be newest-first', () => {
    const backwards = (db: unknown, take: number) =>
      ((db as unknown as string) === 'A' ? [...A].reverse() : [...B].reverse())
        .slice(0, take)
        .map((date) => ({ date }));
    const rows = queryAcross(opened, backwards as never, { sortBy: (r) => String(r.date), limit: 2, offset: 0 });
    // The true two newest are 08-10 and 08-09. Fed oldest-first mailboxes, the helper sorts correctly
    // within what it was handed and returns neither — no error, no gap, just quietly the wrong mail. That
    // is the failure the written contract exists to prevent, and it is why the `descending` option went.
    expect(rows.map((r) => r.date)).toEqual(['2026-08-08', '2026-08-07']);
    expect(rows.map((r) => r.date)).not.toContain('2026-08-10');
  });
});