import { test, expect, Page, Locator, Dialog } from '@playwright/test';

/**
 * Playwright spec for https://hizbu.com/regex/
 * Written against the page source (CodeMirror 6 x2, tabs, #fullscreen checkbox).
 *
 * Requires Playwright >= 1.45 (for the "ControlOrMeta" modifier) and network access
 * to esm.sh (the page loads CodeMirror from there).
 *
 * Reading cursor/selection/doc state uses CodeMirror's EditorView, found through the
 * DOM node (`cmView` / `cmTile` property). If a CodeMirror upgrade ever moves that
 * property, only the `__cmView` init script below needs updating.
 */
const URL = 'http://localhost:4000/regex/';

const KEY = {
  patterns: 'regex_patterns',
  docs: 'regex_documents',
  titles: 'regex_tab_titles',
  active: 'regex_active_tab',
};
const DEFAULT_TITLES = ['Emails & IDs', 'Code Snippet', 'Server Logs'];
const NEW_TAB_TEXT = '// Type or paste text here...\n';

// ---------- locators ----------
const topEditor = (p: Page) => p.locator('#regex-editor .cm-content');
const mainEditor = (p: Page) => p.locator('#cm6-editor .cm-content');
const tabs = (p: Page) => p.locator('#tab-bar [role="tab"]');
const tabLabel = (p: Page, i: number) => tabs(p).nth(i).locator('span[title="Double-click to rename"]');
const tabClose = (p: Page, i: number) => tabs(p).nth(i).locator('.tab-close');
const addTabBtn = (p: Page) => p.locator('#add-tab-btn');
const fullscreen = (p: Page) => p.locator('#fullscreen');
const matchTexts = (p: Page, n: number) =>
  p.locator(`#cm6-editor .cm-regex-match-${n}`).allTextContents();

// ---------- helpers ----------
const docText = (l: Locator): Promise<string> =>
  l.evaluate((el: any) => {
    try { return (window as any).__cmView(el).state.doc.toString(); }
    catch { return [...el.querySelectorAll('.cm-line')].map((x: any) => x.textContent).join('\n'); }
  });

const selection = (l: Locator): Promise<{ anchor: number; head: number }> =>
  l.evaluate((el: any) => {
    const s = (window as any).__cmView(el).state.selection.main;
    return { anchor: s.anchor, head: s.head };
  });

/** Focus the editor WITHOUT changing its selection (unlike click). */
const focusEditor = (l: Locator) => l.evaluate((el: any) => (window as any).__cmView(el).focus());

const storage = (p: Page, key: string) => p.evaluate((k) => localStorage.getItem(k), key);
const storageJson = async (p: Page, key: string) => JSON.parse((await storage(p, key)) ?? 'null');

async function waitReady(p: Page) {
  await expect(p.locator('#loading')).toHaveCount(0, { timeout: 30_000 });
  await expect(topEditor(p)).toBeVisible();
  await expect(mainEditor(p)).toBeVisible();
}

async function reload(p: Page) {
  await p.reload();
  await waitReady(p);
}

/** Replace the whole content of a CodeMirror editor by typing it. */
async function setDoc(p: Page, editor: Locator, lines: string[]) {
  await editor.click();
  await p.keyboard.press('ControlOrMeta+a');
  await p.keyboard.press('Backspace');
  for (let i = 0; i < lines.length; i++) {
    if (i > 0) await p.keyboard.press('Enter');
    if (lines[i]) await p.keyboard.type(lines[i]);
  }
}

/** Click a tab by its label (switches tab). */
const switchTo = (p: Page, i: number) => tabLabel(p, i).click();

async function redo(p: Page) {
  // CodeMirror historyKeymap: Mod-y = redo (Win/Linux), Mod-Shift-z = redo (Mac).
  // Ctrl+Shift+Z is avoided on purpose: on Linux Chromium it was observed to act as undo.
  const isMac = await p.evaluate(() => /Mac/i.test(navigator.platform));
  await p.keyboard.press(isMac ? 'Meta+Shift+z' : 'Control+y');
}

/** Close a tab; asserts the native confirm() text, then accepts or dismisses it. */
async function closeTab(p: Page, index: number, accept: boolean, expectedName?: string) {
  // window.confirm() blocks the page, so click() cannot resolve until the dialog is answered.
  // The handler therefore must be registered BEFORE the click and answer immediately.
  const seen: { type: string; message: string }[] = [];
  const handler = async (d: Dialog) => {
    seen.push({ type: d.type(), message: d.message() });
    await (accept ? d.accept() : d.dismiss());
  };
  p.on('dialog', handler);
  try {
    await tabClose(p, index).click();
  } finally {
    p.off('dialog', handler);
  }

  expect(seen, 'expected exactly one confirm() dialog').toHaveLength(1);
  expect(seen[0].type).toBe('confirm');
  if (expectedName) expect(seen[0].message).toBe(`Are you sure you want to close "${expectedName}"?`);
}

test.beforeEach(async ({ page }) => {
  test.setTimeout(60_000);
  // Exposes CodeMirror's EditorView for a .cm-content node (cmView in older, cmTile in newer builds)
  await page.addInitScript(() => {
    (window as any).__cmView = (el: any) => {
      const t = el.cmView ?? el.cmTile;
      const v = t?.view ?? t?.root?.view ?? t?.rootView?.view;
      if (!v) throw new Error('Could not locate CodeMirror EditorView on .cm-content');
      return v;
    };
  });
  await page.goto(URL);
  await page.evaluate(() => localStorage.clear());
  await reload(page);
});

// =====================================================================
// 0. initial state
// =====================================================================
test.describe('initial state', () => {
  test('loads default tabs, regexes and highlights', async ({ page }) => {
    await expect(tabs(page)).toHaveCount(3);
    await expect(tabs(page).nth(0)).toHaveClass(/active/);
    for (let i = 0; i < 3; i++) await expect(tabLabel(page, i)).toHaveText(DEFAULT_TITLES[i]);

    await expect(topEditor(page)).toContainText('[0-9]{4}-[0-9]{2}-[0-9]{2}');
    await expect.poll(() => matchTexts(page, 0)).toContain('support@example.com');
    await expect.poll(() => matchTexts(page, 1)).toContain('2026-10-17');
  });
});

// =====================================================================
// 1. every regex line is reflected in the lower editor
// =====================================================================
test.describe('regex lines -> lower editor highlights', () => {
  test('each line is reflected (highlight class N = line index % 5) as it is typed', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['abc 123 DEF 456']);
    await setDoc(page, topEditor(page), []); // clear default regexes, leaves top editor focused

    const lines = [
      { text: '/[a-z]+/', expected: ['abc'] },
      { text: '/[0-9]+/', expected: ['123', '456'] },
      { text: '/[A-Z]+/', expected: ['DEF'] },
      { text: '/zzz/', expected: [] },
      { text: '/ /', expected: [' ', ' ', ' '] },
    ];

    for (let i = 0; i < lines.length; i++) {
      if (i > 0) await page.keyboard.press('Enter');
      await page.keyboard.type(lines[i].text);

      // lower editor shows this line's matches with its colour class
      await expect.poll(() => matchTexts(page, i)).toEqual(lines[i].expected);
      // top editor line fringe uses the same colour index
      await expect(page.locator('#regex-editor .cm-line').nth(i))
        .toHaveClass(new RegExp(`cm-regex-line-${i % 5}`));
      // all earlier lines are still reflected
      for (let j = 0; j < i; j++) expect(await matchTexts(page, j)).toEqual(lines[j].expected);
    }
    await expect.poll(() => storage(page, KEY.patterns)).toBe(lines.map((l) => l.text).join('\n'));
  });

  test('colour index wraps after 5 lines', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['w0 w1 w2 w3 w4 w5']);
    await setDoc(page, topEditor(page), [0, 1, 2, 3, 4, 5].map((i) => `/w${i}/`));

    await expect.poll(() => matchTexts(page, 0)).toEqual(['w0', 'w5']);
    for (const n of [1, 2, 3, 4]) expect(await matchTexts(page, n)).toEqual([`w${n}`]);
    await expect(page.locator('#regex-editor .cm-line').nth(5)).toHaveClass(/cm-regex-line-0/);
  });

  test('blank lines are skipped but still consume a line index', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['abc 123']);
    await setDoc(page, topEditor(page), ['/abc/', '', '/123/']);

    await expect.poll(() => matchTexts(page, 0)).toEqual(['abc']);
    expect(await matchTexts(page, 1)).toEqual([]);
    expect(await matchTexts(page, 2)).toEqual(['123']);
  });

  test('editing a line updates highlights; deleting all lines removes them', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['cat dog bird']);
    await setDoc(page, topEditor(page), ['/cat/']);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['cat']);

    // replace line 0
    await page.keyboard.press('ControlOrMeta+Home');
    await page.keyboard.press('Shift+End');
    await page.keyboard.type('/dog/');
    await expect.poll(() => matchTexts(page, 0)).toEqual(['dog']);

    // delete everything
    await page.keyboard.press('ControlOrMeta+a');
    await page.keyboard.press('Backspace');
    await expect(page.locator('#cm6-editor [class*="cm-regex-match-"]')).toHaveCount(0);
  });

  test('editing the lower editor text refreshes highlights', async ({ page }) => {
    await setDoc(page, topEditor(page), ['/foo/']);
    await setDoc(page, mainEditor(page), ['nothing here']);
    await expect(page.locator('#cm6-editor .cm-regex-match-0')).toHaveCount(0);

    await page.keyboard.type(' foo foo');
    await expect.poll(() => matchTexts(page, 0)).toEqual(['foo', 'foo']);
  });

  test('flags: g default, explicit flags honoured, no-g matches only once', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['abc ABC abc']);

    await setDoc(page, topEditor(page), ['/abc/gi']);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['abc', 'ABC', 'abc']);

    await setDoc(page, topEditor(page), ['/abc/i']); // no g -> first match only
    await expect.poll(() => matchTexts(page, 0)).toEqual(['abc']);

    await setDoc(page, topEditor(page), ['abc']); // no slashes -> raw pattern, g flag
    await expect.poll(() => matchTexts(page, 0)).toEqual(['abc', 'abc']);
  });

  test('invalid regex line is ignored without breaking other lines', async ({ page }) => {
    const errors: string[] = [];
    page.on('pageerror', (e) => errors.push(e.message));

    await setDoc(page, mainEditor(page), ['abc 123']);
    await setDoc(page, topEditor(page), ['/(/', '/123/']);

    await expect.poll(() => matchTexts(page, 1)).toEqual(['123']);
    expect(await matchTexts(page, 0)).toEqual([]);
    expect(errors).toEqual([]);
  });

  test('top editor gets one fringe-coloured line per regex line', async ({ page }) => {
    await setDoc(page, topEditor(page), ['a', 'b', 'c', 'd', 'e', 'f']);
    const lines = page.locator('#regex-editor .cm-line');
    await expect(lines).toHaveCount(6);
    for (let i = 0; i < 6; i++) await expect(lines.nth(i)).toHaveClass(new RegExp(`cm-regex-line-${i % 5}`));
  });
});

// =====================================================================
// 2. localStorage
// =====================================================================
test.describe('localStorage', () => {
  test('nothing is written until the first change, then all keys exist', async ({ page }) => {
    expect(await storage(page, KEY.docs)).toBeNull();
    await setDoc(page, topEditor(page), ['/x/']);
    await expect.poll(() => storage(page, KEY.patterns)).toBe('/x/');
    expect(await storageJson(page, KEY.titles)).toEqual(DEFAULT_TITLES);
    expect(await storage(page, KEY.active)).toBe('0');
    expect((await storageJson(page, KEY.docs)).length).toBe(3);
  });

  test('regex editor text is stored and restored', async ({ page }) => {
    await setDoc(page, topEditor(page), ['/one/', '/two/g']);
    await expect.poll(() => storage(page, KEY.patterns)).toBe('/one/\n/two/g');
    await reload(page);
    expect(await docText(topEditor(page))).toBe('/one/\n/two/g');
  });

  test('lower editor text is stored per tab and restored', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['tab zero text']);
    await switchTo(page, 1);
    await setDoc(page, mainEditor(page), ['tab one text']);

    await expect.poll(async () => (await storageJson(page, KEY.docs))?.[0]).toBe('tab zero text');
    expect((await storageJson(page, KEY.docs))[1]).toBe('tab one text');
    expect(await storage(page, KEY.active)).toBe('1');

    await reload(page);
    await expect(tabs(page).nth(1)).toHaveClass(/active/); // active tab restored
    expect(await docText(mainEditor(page))).toBe('tab one text');
    await switchTo(page, 0);
    expect(await docText(mainEditor(page))).toBe('tab zero text');
  });

  test('tab titles and tab count are stored and restored', async ({ page }) => {
    await addTabBtn(page).click();
    await tabLabel(page, 0).dblclick();
    await page.locator('#tab-bar input').fill('Renamed');
    await page.keyboard.press('Enter');

    await expect.poll(() => storageJson(page, KEY.titles)).toEqual(['Renamed', 'Code Snippet', 'Server Logs', 'Dataset 4']);
    await reload(page);
    await expect(tabs(page)).toHaveCount(4);
    await expect(tabLabel(page, 0)).toHaveText('Renamed');
    await expect(tabLabel(page, 3)).toHaveText('Dataset 4');
  });

  test('highlights are re-applied after reload', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['needle hay needle']);
    await setDoc(page, topEditor(page), ['/needle/']);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['needle', 'needle']);
    await reload(page);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['needle', 'needle']);
  });

  test('clearing localStorage resets to defaults', async ({ page }) => {
    await setDoc(page, topEditor(page), ['/wiped/']);
    await expect.poll(() => storage(page, KEY.patterns)).toBe('/wiped/');
    await page.evaluate(() => localStorage.clear());
    await reload(page);
    await expect(tabs(page)).toHaveCount(3);
    expect(await docText(topEditor(page))).not.toContain('wiped');
  });
});

// =====================================================================
// 3. rename tab on double click
// =====================================================================
test.describe('rename tab', () => {
  const input = (p: Page) => p.locator('#tab-bar input');

  test('double click shows a focused input with the current name selected', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await expect(input(page)).toBeVisible();
    await expect(input(page)).toBeFocused();
    await expect(input(page)).toHaveValue(DEFAULT_TITLES[0]);
    expect(await input(page).evaluate((el: HTMLInputElement) => el.selectionEnd! - el.selectionStart!))
      .toBe(DEFAULT_TITLES[0].length);
  });

  test('Enter commits, trims, and persists across reload', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await input(page).fill('  My Tab  ');
    await page.keyboard.press('Enter');

    await expect(input(page)).toHaveCount(0);
    await expect(tabLabel(page, 0)).toHaveText('My Tab');
    await expect.poll(async () => (await storageJson(page, KEY.titles))[0]).toBe('My Tab');
    await reload(page);
    await expect(tabLabel(page, 0)).toHaveText('My Tab');
  });

  test('Escape cancels', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await input(page).fill('nope');
    await page.keyboard.press('Escape');
    await expect(tabLabel(page, 0)).toHaveText(DEFAULT_TITLES[0]);
  });

  test('blur commits', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await input(page).fill('Blurred');
    await mainEditor(page).click();
    await expect(tabLabel(page, 0)).toHaveText('Blurred');
  });

  test('empty / whitespace-only name keeps the old name', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await input(page).fill('   ');
    await page.keyboard.press('Enter');
    await expect(tabLabel(page, 0)).toHaveText(DEFAULT_TITLES[0]);
  });

  test('typing in the rename input (incl. Enter) never edits the editors', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['keep me']);
    await setDoc(page, topEditor(page), ['/keep/']);
    await tabLabel(page, 0).dblclick();
    await input(page).fill('abc');
    await page.keyboard.press('Enter');
    expect(await docText(mainEditor(page))).toBe('keep me');
    expect(await docText(topEditor(page))).toBe('/keep/');
  });

  test('renaming a non-active tab also works (and activates it)', async ({ page }) => {
    await tabLabel(page, 2).dblclick();
    await input(page).fill('Logs!');
    await page.keyboard.press('Enter');
    await expect(tabLabel(page, 2)).toHaveText('Logs!');
    await expect(tabs(page).nth(2)).toHaveClass(/active/);
  });

  test('clicking inside the rename input does not switch tabs', async ({ page }) => {
    await tabLabel(page, 0).dblclick();
    await input(page).click();
    await expect(input(page)).toBeVisible();
    await expect(tabs(page).nth(0)).toHaveClass(/active/);
  });
});

// =====================================================================
// 4. add / delete tab (with confirmation)
// =====================================================================
test.describe('add and delete tabs', () => {
  test('add creates "Dataset N" with starter text and activates it', async ({ page }) => {
    await addTabBtn(page).click();
    await expect(tabs(page)).toHaveCount(4);
    await expect(tabLabel(page, 3)).toHaveText('Dataset 4');
    await expect(tabs(page).nth(3)).toHaveClass(/active/);
    expect(await docText(mainEditor(page))).toBe(NEW_TAB_TEXT);

    await addTabBtn(page).click();
    await expect(tabLabel(page, 4)).toHaveText('Dataset 5');
  });

  test('add keeps the previous tab content intact', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['original']);
    await addTabBtn(page).click();
    await switchTo(page, 0);
    expect(await docText(mainEditor(page))).toBe('original');
  });

  test('delete shows confirm() with the tab name; cancelling keeps the tab', async ({ page }) => {
    await closeTab(page, 1, false, 'Code Snippet');
    await expect(tabs(page)).toHaveCount(3);
    await expect(tabLabel(page, 1)).toHaveText('Code Snippet');
  });

  test('accepting removes the tab and persists', async ({ page }) => {
    await closeTab(page, 1, true, 'Code Snippet');
    await expect(tabs(page)).toHaveCount(2);
    await expect(tabLabel(page, 0)).toHaveText('Emails & IDs');
    await expect(tabLabel(page, 1)).toHaveText('Server Logs');

    await expect.poll(() => storageJson(page, KEY.titles)).toEqual(['Emails & IDs', 'Server Logs']);
    expect((await storageJson(page, KEY.docs)).length).toBe(2);
    await reload(page);
    await expect(tabs(page)).toHaveCount(2);
  });

  test('close click does not switch to the tab being closed when cancelled', async ({ page }) => {
    await closeTab(page, 2, false);
    await expect(tabs(page).nth(0)).toHaveClass(/active/);
  });

  test('deleting a tab BEFORE the active one keeps the same tab and content active', async ({ page }) => {
    await switchTo(page, 2);
    const before = await docText(mainEditor(page));
    await closeTab(page, 0, true);
    await expect(tabs(page)).toHaveCount(2);
    await expect(tabs(page).nth(1)).toHaveClass(/active/);
    await expect(tabLabel(page, 1)).toHaveText('Server Logs');
    expect(await docText(mainEditor(page))).toBe(before);
  });

  test('deleting the active LAST tab activates the new last tab', async ({ page }) => {
    await switchTo(page, 2);
    await closeTab(page, 2, true);
    await expect(tabs(page)).toHaveCount(2);
    await expect(tabs(page).nth(1)).toHaveClass(/active/);
    await expect(tabLabel(page, 1)).toHaveText('Code Snippet');
  });

  test('deleting the active FIRST tab activates the tab that took its place', async ({ page }) => {
    await closeTab(page, 0, true);
    await expect(tabs(page).nth(0)).toHaveClass(/active/);
    await expect(tabLabel(page, 0)).toHaveText('Code Snippet');
  });

  test('last remaining tab cannot be closed (no close button)', async ({ page }) => {
    await closeTab(page, 0, true);
    await closeTab(page, 0, true);
    await expect(tabs(page)).toHaveCount(1);
    await expect(page.locator('#tab-bar .tab-close')).toHaveCount(0);
  });

  test('deleted tab edits do not leak into remaining tabs', async ({ page }) => {
    await switchTo(page, 1);
    await setDoc(page, mainEditor(page), ['doomed']);
    await closeTab(page, 1, true);
    for (let i = 0; i < 2; i++) {
      await switchTo(page, i);
      expect(await docText(mainEditor(page))).not.toBe('doomed');
    }
  });
});

// =====================================================================
// 5. fullscreen (body margin / padding / max-width)
// =====================================================================
test.describe('fullscreen', () => {
  const bodyMetrics = (p: Page) =>
    p.evaluate(() => {
      const cs = getComputedStyle(document.body);
      return {
        margin: [cs.marginTop, cs.marginRight, cs.marginBottom, cs.marginLeft],
        padding: [cs.paddingTop, cs.paddingRight, cs.paddingBottom, cs.paddingLeft],
        maxWidth: cs.maxWidth,
        inline: ['margin', 'padding', 'max-width'].map((k) => document.body.style.getPropertyValue(k)),
      };
    });
  const ZERO = ['0px', '0px', '0px', '0px'];

  test('checkbox is unchecked by default', async ({ page }) => {
    await expect(fullscreen(page)).not.toBeChecked();
  });

  test('checking removes body margin & padding and lifts max-width', async ({ page }) => {
    await fullscreen(page).check();
    const m = await bodyMetrics(page);
    expect(m.margin).toEqual(ZERO);
    expect(m.padding).toEqual(ZERO);
    expect(m.maxWidth).toBe('none');
    expect(m.inline).toEqual(['0px', '0px', 'none']);

    const box = (await page.locator('body').boundingBox())!;
    expect(box.x).toBe(0);
    const clientWidth = await page.evaluate(() => document.documentElement.clientWidth);
    expect(Math.round(box.width)).toBe(clientWidth);
  });

  test('unchecking restores the original body styles exactly', async ({ page }) => {
    const before = await bodyMetrics(page);
    await fullscreen(page).check();
    await fullscreen(page).uncheck();
    expect(await bodyMetrics(page)).toEqual(before);
  });

  test('editors become at least as wide in fullscreen', async ({ page }) => {
    const wBefore = (await page.locator('#regex-editor').boundingBox())!.width;
    await fullscreen(page).check();
    const wAfter = (await page.locator('#regex-editor').boundingBox())!.width;
    expect(wAfter).toBeGreaterThanOrEqual(wBefore);
  });

  test('fullscreen survives tab switching, add/rename and typing', async ({ page }) => {
    await fullscreen(page).check();
    await switchTo(page, 1);
    await addTabBtn(page).click();
    await setDoc(page, topEditor(page), ['/x/']);
    await tabLabel(page, 0).dblclick();
    await page.locator('#tab-bar input').fill('FS');
    await page.keyboard.press('Enter');

    const m = await bodyMetrics(page);
    expect(m.margin).toEqual(ZERO);
    expect(m.padding).toEqual(ZERO);
    await expect(fullscreen(page)).toBeChecked();
  });

  test('toggling repeatedly is stable', async ({ page }) => {
    const before = await bodyMetrics(page);
    for (let i = 0; i < 3; i++) {
      await fullscreen(page).check();
      expect((await bodyMetrics(page)).padding).toEqual(ZERO);
      await fullscreen(page).uncheck();
    }
    expect(await bodyMetrics(page)).toEqual(before);
  });
});

// =====================================================================
// 6. undo / redo / selection / cursor preserved across tab movement
//    (each tab has its own EditorState in the lower editor)
// =====================================================================
test.describe('per-tab editor state', () => {
  const HISTORY_GAP = 700; // CodeMirror groups edits within 500ms into one undo step

  test('cursor position is preserved per tab', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['line one', 'line two', 'line three']);
    await page.keyboard.press('ControlOrMeta+Home');
    await page.keyboard.press('ArrowDown');
    for (let i = 0; i < 4; i++) await page.keyboard.press('ArrowRight');
    const cursor0 = await selection(mainEditor(page));
    expect(cursor0.head).toBe(9 + 4);
    expect(cursor0.anchor).toBe(cursor0.head);

    await switchTo(page, 1);
    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+End');
    const len1 = (await docText(mainEditor(page))).length;
    expect((await selection(mainEditor(page))).head).toBe(len1);

    await switchTo(page, 0);
    expect(await selection(mainEditor(page))).toEqual(cursor0);

    // typing at the restored position lands exactly there
    await focusEditor(mainEditor(page));
    await page.keyboard.type('X');
    expect(await docText(mainEditor(page))).toBe('line one\nlineX two\nline three');

    await switchTo(page, 1);
    expect((await selection(mainEditor(page))).head).toBe(len1);
  });

  test('selection range is preserved per tab', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['hello brave new world']);
    await page.keyboard.press('ControlOrMeta+Home');
    for (let i = 0; i < 6; i++) await page.keyboard.press('ArrowRight');
    for (let i = 0; i < 5; i++) await page.keyboard.press('Shift+ArrowRight'); // "brave"
    expect(await selection(mainEditor(page))).toEqual({ anchor: 6, head: 11 });

    await switchTo(page, 1);
    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+a');
    const all1 = await selection(mainEditor(page));
    expect(all1.anchor).toBe(0);
    expect(all1.head).toBeGreaterThan(0);

    await switchTo(page, 0);
    expect(await selection(mainEditor(page))).toEqual({ anchor: 6, head: 11 });
    await switchTo(page, 1);
    expect(await selection(mainEditor(page))).toEqual(all1);

    // selection is real: typing replaces exactly the preserved range
    await switchTo(page, 0);
    await focusEditor(mainEditor(page));
    await page.keyboard.type('BRAVE');
    expect(await docText(mainEditor(page))).toBe('hello BRAVE new world');
  });

  test('selection direction (anchor vs head) is preserved', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['abcdefghij']);
    await page.keyboard.press('ControlOrMeta+End');
    for (let i = 0; i < 4; i++) await page.keyboard.press('Shift+ArrowLeft'); // backwards
    const sel = await selection(mainEditor(page));
    expect(sel.head).toBeLessThan(sel.anchor);

    await switchTo(page, 1);
    await switchTo(page, 0);
    expect(await selection(mainEditor(page))).toEqual(sel);
  });

  test('undo history is preserved per tab and does not leak between tabs', async ({ page }) => {
    // tab 0: three separate undo steps
    await setDoc(page, mainEditor(page), ['base']);
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type(' one');
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type(' two');
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type(' three');
    expect(await docText(mainEditor(page))).toBe('base one two three');

    // tab 1: its own edit
    await switchTo(page, 1);
    const tab1Original = await docText(mainEditor(page));
    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+End');
    await page.keyboard.type(' T1');
    await page.waitForTimeout(HISTORY_GAP);
    expect(await docText(mainEditor(page))).toBe(tab1Original + ' T1');

    // back to tab 0: undo works step by step, with no tab-1 text involved
    await switchTo(page, 0);
    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe('base one two');
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe('base one');

    // tab 1: its undo only removes its own edit
    await switchTo(page, 1);
    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe(tab1Original);
    await page.keyboard.press('ControlOrMeta+z'); // nothing more to undo
    expect(await docText(mainEditor(page))).toBe(tab1Original);

    // tab 0 untouched by tab 1's undo
    await switchTo(page, 0);
    expect(await docText(mainEditor(page))).toBe('base one');
  });

  test('redo history is preserved across tab switches', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['alpha']);
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type(' beta');
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type(' gamma');
    await page.keyboard.press('ControlOrMeta+z');
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe('alpha');

    await switchTo(page, 2);
    await focusEditor(mainEditor(page));
    await page.keyboard.type('noise');
    await page.waitForTimeout(HISTORY_GAP);

    await switchTo(page, 0);
    expect(await docText(mainEditor(page))).toBe('alpha');
    await focusEditor(mainEditor(page));
    await redo(page);
    expect(await docText(mainEditor(page))).toBe('alpha beta');
    await redo(page);
    expect(await docText(mainEditor(page))).toBe('alpha beta gamma');
  });

  test('undo restores selection/cursor consistently after returning to a tab', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['12345']);
    await page.waitForTimeout(HISTORY_GAP);
    await page.keyboard.type('678');
    await page.keyboard.press('Home');
    const cursor = await selection(mainEditor(page));

    await switchTo(page, 1);
    await switchTo(page, 0);
    expect(await selection(mainEditor(page))).toEqual(cursor);

    await focusEditor(mainEditor(page));
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe('12345');
  });

  test('a newly added tab has a fresh history (undo is a no-op) and cursor at start', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['something']);
    await addTabBtn(page).click();
    await focusEditor(mainEditor(page));
    expect(await selection(mainEditor(page))).toEqual({ anchor: 0, head: 0 });
    await page.keyboard.press('ControlOrMeta+z');
    expect(await docText(mainEditor(page))).toBe(NEW_TAB_TEXT);
  });

  test('state survives many rapid tab switches', async ({ page }) => {
    await setDoc(page, mainEditor(page), ['AAAAAAAAAA']);
    await page.keyboard.press('ControlOrMeta+Home');
    for (let i = 0; i < 2; i++) await page.keyboard.press('ArrowRight');
    for (let i = 0; i < 3; i++) await page.keyboard.press('Shift+ArrowRight');
    const selA = await selection(mainEditor(page));

    await switchTo(page, 1);
    await setDoc(page, mainEditor(page), ['BBBBBBBBBB']);
    await page.keyboard.press('ControlOrMeta+Home');
    for (let i = 0; i < 6; i++) await page.keyboard.press('ArrowRight');
    const selB = await selection(mainEditor(page));

    for (let i = 0; i < 5; i++) {
      await switchTo(page, 0);
      await switchTo(page, 1);
    }
    expect(await selection(mainEditor(page))).toEqual(selB);
    await switchTo(page, 0);
    expect(await selection(mainEditor(page))).toEqual(selA);
  });

  test('highlights are refreshed per tab when switching (stale regex queries)', async ({ page }) => {
    await setDoc(page, topEditor(page), ['/zqx/']);
    await setDoc(page, mainEditor(page), ['zqx qqq']);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['zqx']);

    await switchTo(page, 1);
    await expect(page.locator('#cm6-editor .cm-regex-match-0')).toHaveCount(0);

    // change the regex while on tab 1, then return to tab 0: must use the NEW regex
    await setDoc(page, topEditor(page), ['/qqq/']);
    await switchTo(page, 0);
    await expect.poll(() => matchTexts(page, 0)).toEqual(['qqq']);
  });

  test('switching tabs does not alter the regex (top) editor', async ({ page }) => {
    await setDoc(page, topEditor(page), ['/keep/', '/me/']);
    await switchTo(page, 1);
    await switchTo(page, 2);
    expect(await docText(topEditor(page))).toBe('/keep/\n/me/');
  });
});