// The two-part fallback gate.
//
// `lib/jmap/client.ts`'s read methods swallow their own errors and return
// plausible success, so a "looks empty" result is NOT evidence of a network
// failure - it is also what a genuinely empty folder returns, and
// `getMailboxes()` fabricates a synthetic Inbox rather than throwing. Falling back
// on the shape alone would serve stale replica rows over a folder the user had
// just emptied. So the gate is: suspicious result AND a `fetch` rejection recorded
// during that exact call.

import { beforeEach, describe, expect, it, vi } from 'vitest';
import type { IJMAPClient } from '@/lib/jmap/client-interface';
import type { Email, Mailbox } from '@/lib/jmap/types';
import { noteTransportFailure, resetTransportHealth } from '@/lib/jmap/transport-health';

const readOfflineMailboxes = vi.fn();
const readOfflineList = vi.fn();
const readOfflineMessage = vi.fn();
const isReplicaUnavailable = vi.fn(() => false);

vi.mock('@/lib/offline-replica-client', () => ({
  readOfflineMailboxes: (...a: unknown[]) => readOfflineMailboxes(...a),
  readOfflineList: (...a: unknown[]) => readOfflineList(...a),
  readOfflineMessage: (...a: unknown[]) => readOfflineMessage(...a),
  isReplicaUnavailable: () => isReplicaUnavailable(),
}));

vi.mock('@/stores/account-store', () => ({
  useAccountStore: {
    getState: () => ({
      accounts: [{ id: 'alice@mail.example.org', cookieSlot: 3, serverIdentifiers: [] }],
    }),
  },
}));

const { withOfflineFallback } = await import('@/lib/offline-fallback-client');

function replicaEmail(id: string): Email {
  return {
    id, threadId: 't', mailboxIds: { inbox: true }, keywords: {}, size: 1,
    receivedAt: '2026-08-01T00:00:00.000Z', hasAttachment: false,
    htmlBody: [{ partId: '1', blobId: 'b', size: 1, type: 'text/html' }],
    bodyValues: { '1': { value: '<p>from the replica</p>' } },
  };
}

interface Stub extends Partial<IJMAPClient> {
  getEmail: IJMAPClient['getEmail'];
  getEmails: IJMAPClient['getEmails'];
  getMailboxes: IJMAPClient['getMailboxes'];
  getAllMailboxes: IJMAPClient['getAllMailboxes'];
}

/** Reproduces the client's real error-swallowing shapes. */
function stubClient(overrides: Partial<Stub> = {}): IJMAPClient {
  const stub = {
    getUsername: () => 'alice',
    getServerUrl: () => 'https://mail.example.org',
    getAccountId: () => 'primary',
    getEmail: async () => null,
    getEmails: async () => ({ emails: [] as Email[], hasMore: false, total: 0 }),
    getMailboxes: async () => ([
      // The exact placeholder client.ts fabricates on failure.
      { id: 'INBOX', name: 'Inbox', role: 'inbox', sortOrder: 0, totalEmails: 0,
        unreadEmails: 0, totalThreads: 0, unreadThreads: 0, isSubscribed: true,
        myRights: {} } as unknown as Mailbox,
    ]),
    getAllMailboxes: async () => ([
      { id: 'INBOX', name: 'Inbox', role: 'inbox', sortOrder: 0, totalEmails: 0,
        unreadEmails: 0, totalThreads: 0, unreadThreads: 0, isSubscribed: true,
        myRights: {} } as unknown as Mailbox,
    ]),
    ...overrides,
  };
  return stub as unknown as IJMAPClient;
}

describe('withOfflineFallback', () => {
  beforeEach(() => {
    resetTransportHealth();
    vi.clearAllMocks();
    isReplicaUnavailable.mockReturnValue(false);
  });

  it('does NOT consult the replica when the server answered "empty"', async () => {
    // The whole point. An empty folder must render empty, not as whatever the
    // replica last held.
    const client = withOfflineFallback(stubClient());
    const result = await client.getEmails('inbox');
    expect(result.emails).toEqual([]);
    expect(readOfflineList).not.toHaveBeenCalled();

    expect(await client.getEmail('e1')).toBeNull();
    expect(readOfflineMessage).not.toHaveBeenCalled();
  });

  it('consults the replica when a transport failure happened DURING the call', async () => {
    readOfflineList.mockResolvedValue({
      emails: [replicaEmail('e1')], total: 1, hasMore: false,
    });
    const client = withOfflineFallback(
      stubClient({
        getEmails: async () => {
          // What authenticatedFetch does when `fetch` rejects.
          noteTransportFailure();
          return { emails: [], hasMore: false, total: 0 };
        },
      }),
    );
    const result = await client.getEmails('inbox', undefined, 25, 0);
    expect(result.emails.map((e) => e.id)).toEqual(['e1']);
    expect(result.total).toBe(1);
    // And it asks for the right slot, so a multi-account shell reads the right file.
    expect(readOfflineList).toHaveBeenCalledWith('inbox', { limit: 25, offset: 0, slot: 3 });
  });

  it('ignores a stale transport failure from BEFORE the call', async () => {
    // The counter is sampled per call precisely so an old failure cannot make a
    // later successful-but-empty read look offline.
    noteTransportFailure();
    const client = withOfflineFallback(stubClient());
    await client.getEmails('inbox');
    expect(readOfflineList).not.toHaveBeenCalled();
  });

  it('serves a full message from the replica, but refuses an envelope-only hit', async () => {
    // An envelope with no bodyValues would render blank AND leave the viewer's
    // isBodyLoading gate stuck on its skeleton, which is worse than saying the
    // message is unavailable.
    readOfflineMessage.mockResolvedValue({ email: replicaEmail('e1'), hasBody: true });
    const client = withOfflineFallback(
      stubClient({ getEmail: async () => { noteTransportFailure(); return null; } }),
    );
    const email = await client.getEmail('e1');
    expect(email?.bodyValues?.['1'].value).toContain('from the replica');

    resetTransportHealth();
    readOfflineMessage.mockResolvedValue({ email: replicaEmail('e2'), hasBody: false });
    const client2 = withOfflineFallback(
      stubClient({ getEmail: async () => { noteTransportFailure(); return null; } }),
    );
    expect(await client2.getEmail('e2')).toBeNull();
  });

  it('recognises the synthetic Inbox placeholder and replaces it', async () => {
    readOfflineMailboxes.mockResolvedValue([
      { id: 'mb1', name: 'Inbox', role: 'inbox', sortOrder: 0, totalEmails: 9, unreadEmails: 2,
        totalThreads: 9, unreadThreads: 2, isSubscribed: true, myRights: {} } as unknown as Mailbox,
    ]);
    const client = withOfflineFallback(
      stubClient({
        getAllMailboxes: async () => {
          noteTransportFailure();
          return [
            { id: 'INBOX', name: 'Inbox', role: 'inbox', sortOrder: 0, totalEmails: 0,
              unreadEmails: 0, totalThreads: 0, unreadThreads: 0, isSubscribed: true,
              myRights: {} } as unknown as Mailbox,
          ];
        },
      }),
    );
    const mailboxes = await client.getAllMailboxes();
    expect(mailboxes.map((m) => m.id)).toEqual(['mb1']);
  });

  it('keeps a REAL single-mailbox server result even after a transport failure', async () => {
    // A genuine server that happens to return one inbox has a real id and real
    // counts; only the exact placeholder shape may be replaced.
    const real = {
      id: 'real-inbox-id', name: 'Inbox', role: 'inbox', sortOrder: 0, totalEmails: 12,
      unreadEmails: 1, totalThreads: 12, unreadThreads: 1, isSubscribed: true, myRights: {},
    } as unknown as Mailbox;
    const client = withOfflineFallback(
      stubClient({ getAllMailboxes: async () => { noteTransportFailure(); return [real]; } }),
    );
    expect((await client.getAllMailboxes())[0].id).toBe('real-inbox-id');
    expect(readOfflineMailboxes).not.toHaveBeenCalled();
  });

  it('never answers a read scoped to a delegated account', async () => {
    // v1 replicates the PRIMARY mail account only, so the replica has no rows for
    // a shared account and answering "empty" would be worse than the client's own.
    const client = withOfflineFallback(
      stubClient({
        getEmails: async () => { noteTransportFailure(); return { emails: [], hasMore: false, total: 0 }; },
      }),
    );
    await client.getEmails('inbox', 'someone-elses-account');
    expect(readOfflineList).not.toHaveBeenCalled();
  });

  it('never answers a keyword- or category-filtered query', async () => {
    // Those are server-side queries the replica does not reproduce. Serving an
    // unfiltered page in their place would silently show the wrong set.
    const failing = async () => { noteTransportFailure(); return { emails: [], hasMore: false, total: 0 }; };
    const c1 = withOfflineFallback(stubClient({ getEmails: failing }));
    await c1.getEmails('inbox', undefined, 25, 0, '$flagged');
    expect(readOfflineList).not.toHaveBeenCalled();

    resetTransportHealth();
    const c2 = withOfflineFallback(stubClient({ getEmails: failing }));
    await c2.getEmails('inbox', undefined, 25, 0, undefined, true, { from: 'x' });
    expect(readOfflineList).not.toHaveBeenCalled();
  });

  it('stops asking once the replica reports itself absent', async () => {
    isReplicaUnavailable.mockReturnValue(true);
    const client = withOfflineFallback(
      stubClient({ getEmail: async () => { noteTransportFailure(); return null; } }),
    );
    expect(await client.getEmail('e1')).toBeNull();
    expect(readOfflineMessage).not.toHaveBeenCalled();
  });

  it('is idempotent, so re-wrapping a client does not stack fallbacks', async () => {
    readOfflineMessage.mockResolvedValue({ email: replicaEmail('e1'), hasBody: true });
    const base = stubClient({ getEmail: async () => { noteTransportFailure(); return null; } });
    const once = withOfflineFallback(base);
    const twice = withOfflineFallback(once);
    expect(twice).toBe(once);
    await twice.getEmail('e1');
    expect(readOfflineMessage).toHaveBeenCalledTimes(1);
  });
});