/**
 * LivePreview — busy overlay guard (spec §04; arch §10.2).
 *
 * The render pipeline is integration-heavy (vega-embed, IndexedDB, Monaco); the
 * busy OVERLAY itself is purely a function of `PreviewStore.busy`. These tests
 * set that flag directly and assert the DOM result — no timing, no mocking of the
 * async render path.
 */

import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
import { act } from 'react';
import { createRoot, type Root } from 'react-dom/client';
import { usePreviewStore } from '../stores/PreviewStore';
import { useSnippetStore } from '../stores/SnippetStore';
import { useDatasetStore } from '../stores/DatasetStore';
import { LivePreview } from './LivePreview';

// Controllable renderSpec: each call gets an id and parks a resolver in `H.pending`
// so a test can decide exactly when (and in what order) embeds settle — the only
// way to exercise the overlapping-render serialization deterministically. `destroy`
// records its id and clears the node, mirroring the real handle (which calls
// node.replaceChildren()), so a wrongful blank would be observable.
const H = vi.hoisted(() => ({
  calls: 0,
  pending: [] as Array<() => void>,
  destroyed: [] as number[],
}));
vi.mock('../services/chart-renderer', () => ({
  renderSpec: (node: HTMLElement) => {
    const id = ++H.calls;
    return new Promise((resolve) => {
      H.pending.push(() => {
        node.replaceChildren(); // a real embed wipes then rebuilds the host
        const mark = document.createElement('div');
        mark.dataset.render = String(id);
        node.appendChild(mark);
        resolve({
          destroy() {
            node.replaceChildren();
            H.destroyed.push(id);
          },
          resize() {},
        });
      });
    });
  },
}));
vi.mock('./SettingsPopover', () => ({
  SettingsPopover: () => null,
  SettingRow: () => null,
  RangeControl: () => null,
}));
// Isolate the busy-overlay assertions (which locate the overlay by its
// `aria-hidden="true"`) from the export control's own decorative icon: the
// per-chart export is a sibling header control, mocked out like SettingsPopover.
vi.mock('./ChartExport', () => ({ ChartExport: () => null }));

(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;

let container: HTMLDivElement;
let root: Root;

beforeEach(() => {
  H.calls = 0;
  H.pending.length = 0;
  H.destroyed.length = 0;
  usePreviewStore.setState({ error: null, busy: false });
  useSnippetStore.getState().reset();
  useDatasetStore.getState().reset();

  container = document.createElement('div');
  document.body.appendChild(container);
  root = createRoot(container);
  act(() => root.render(<LivePreview />));
});

afterEach(() => {
  act(() => root.unmount());
  container.remove();
  usePreviewStore.setState({ error: null, busy: false });
  vi.clearAllMocks();
});

describe('LivePreview busy overlay', () => {
  test('does not render the busy overlay when busy=false', () => {
    // The overlay element should not be in the DOM at all during normal operation.
    expect(container.querySelector('[aria-hidden="true"]')).toBeNull();
  });

  test('renders the busy overlay when PreviewStore.busy=true', () => {
    act(() => usePreviewStore.setState({ busy: true }));
    const overlay = container.querySelector('[aria-hidden="true"]');
    expect(overlay).not.toBeNull();
  });

  test('overlay carries a visible label for sighted users', () => {
    act(() => usePreviewStore.setState({ busy: true }));
    const label = container.querySelector('[aria-hidden="true"]')?.textContent;
    expect(label).toMatch(/rendering/i);
  });

  test('the preview body carries aria-busy=true when busy', () => {
    act(() => usePreviewStore.setState({ busy: true }));
    // The body element has aria-busy when the store says busy.
    const busyEl = container.querySelector('[aria-busy="true"]');
    expect(busyEl).not.toBeNull();
  });

  test('aria-busy is absent when busy=false (no aria-busy="false" noise)', () => {
    // aria-busy="false" is technically valid but needlessly verbose; we omit it.
    expect(container.querySelector('[aria-busy]')).toBeNull();
  });

  test('overlay disappears when busy returns to false', () => {
    act(() => usePreviewStore.setState({ busy: true }));
    expect(container.querySelector('[aria-hidden="true"]')).not.toBeNull();
    act(() => usePreviewStore.setState({ busy: false }));
    expect(container.querySelector('[aria-hidden="true"]')).toBeNull();
  });
});

describe('LivePreview render serialization', () => {
  /** Drive the debounced render effect to completion under fake timers. */
  const tick = (ms = 6000) => act(async () => void (await vi.advanceTimersByTimeAsync(ms)));

  test('a second render waits for the in-flight one, which is finalized when superseded', async () => {
    vi.useFakeTimers();
    try {
      // Render A: valid, ref-less spec so prepareSpecForRender passes and we reach
      // renderSpec (which now parks, awaiting our resolver).
      act(() => {
        useSnippetStore.setState({ draftText: '{"data":{"values":[]},"mark":"point"}' });
      });
      await tick();
      expect(H.calls).toBe(1); // A invoked renderSpec and is in flight

      // Render B arrives while A is still embedding. It must NOT start a second
      // embed on the shared node — it queues behind A's lock.
      act(() => {
        useSnippetStore.setState({ draftText: '{"data":{"values":[]},"mark":"bar"}' });
      });
      await tick();
      expect(H.calls).toBe(1); // still only A's embed; B is serialized behind it

      // A settles. It was superseded by B, so its handle is finalized (destroy),
      // and only now does B acquire the lock and start its embed.
      act(() => H.pending[0]());
      await tick(0);
      expect(H.destroyed).toContain(1); // superseded A finalized
      expect(H.calls).toBe(2); // B now embeds

      // B settles and becomes the live chart — never destroyed, and its node
      // content survives (A's finalize ran before B drew, so nothing blanked it).
      act(() => H.pending[1]());
      await tick(0);
      expect(H.destroyed).not.toContain(2);
      expect(container.querySelector('[data-render="2"]')).not.toBeNull();
    } finally {
      vi.useRealTimers();
    }
  });

  test('clearing the editor invalidates a pending render (no stale redraw)', async () => {
    vi.useFakeTimers();
    try {
      act(() => {
        useSnippetStore.setState({ draftText: '{"data":{"values":[]},"mark":"point"}' });
      });
      await tick();
      expect(H.calls).toBe(1); // render A in flight

      // Editor cleared while A embeds. The clear advances the generation token, so
      // when A finally resolves it knows it is stale and finalizes instead of
      // committing — the pane ends up empty, not showing A's chart.
      act(() => {
        useSnippetStore.setState({ draftText: '' });
      });
      await tick();
      act(() => H.pending[0]());
      await tick(0);

      expect(H.destroyed).toContain(1); // stale A finalized, not committed
      expect(container.querySelector('[data-render="1"]')).toBeNull();
    } finally {
      vi.useRealTimers();
    }
  });
});
