/**
 * @fileoverview Unit tests for the CJK IME input module (input-cjk.js).
 *
 * Loads the browser module into a vm sandbox (no real DOM) and drives fake
 * composition/keydown/input event sequences against a stub textarea.
 * Focus: the intermittent "Chinese characters silently lost" failure modes —
 * stuck composition state, deferred flush racing the next composition, and
 * the keydown-echo suppression window swallowing a real IME commit.
 */
import { readFileSync } from 'node:fs';
import { resolve } from 'node:path';
import vm from 'node:vm';
import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';

const PHANTOM = '​';

interface FakeTextarea {
  value: string;
  valueWrites: number;
  blur: () => void;
  focus: () => void;
  classList: { contains: (c: string) => boolean };
  setSelectionRange: () => void;
  addEventListener: (ev: string, fn: (e?: unknown) => void) => void;
  removeEventListener: (ev: string, fn: (e?: unknown) => void) => void;
  fire: (ev: string, arg?: Record<string, unknown>) => void;
}

function makeTextarea(): FakeTextarea {
  const listeners = new Map<string, Array<(e?: unknown) => void>>();
  let val = '';
  return {
    get value() {
      return val;
    },
    set value(v: string) {
      this.valueWrites++;
      val = v;
    },
    valueWrites: 0,
    blur: () => {},
    focus: () => {},
    classList: { contains: (c: string) => c === 'cjk-input-visible' },
    setSelectionRange: () => {},
    addEventListener: (ev, fn) => {
      const list = listeners.get(ev) ?? [];
      listeners.set(ev, [...list, fn]);
    },
    removeEventListener: (ev, fn) => {
      const list = listeners.get(ev) ?? [];
      listeners.set(
        ev,
        list.filter((f) => f !== fn)
      );
    },
    fire(ev, arg = {}) {
      const base = { preventDefault: () => {}, stopPropagation: () => {}, ...arg };
      for (const fn of listeners.get(ev) ?? []) fn(base);
    },
  };
}

function loadCjkHarness() {
  const textarea = makeTextarea();
  const sent: string[] = [];
  const windowObj: Record<string, unknown> = {};
  const documentObj = {
    getElementById: (id: string) => (id === 'cjkInput' ? textarea : null),
    activeElement: null as unknown,
  };

  // Delegating closures so vitest fake timers (which patch the test realm's
  // globals) govern the vm context's timers/clock too.
  const context = vm.createContext({
    window: windowObj,
    document: documentObj,
    setTimeout: (fn: () => void, ms?: number) => setTimeout(fn, ms),
    clearTimeout: (t: ReturnType<typeof setTimeout>) => clearTimeout(t),
    performance: { now: () => performance.now() },
    console,
  });

  const src = readFileSync(resolve(import.meta.dirname, '../src/web/public/input-cjk.js'), 'utf8');
  vm.runInContext(src, context, { filename: 'input-cjk.js' });
  const CjkInput = vm.runInContext('CjkInput', context);

  CjkInput.init({ send: (text: string) => sent.push(text) });
  textarea.fire('focus');

  return { CjkInput, textarea, sent, windowObj, documentObj };
}

describe('CJK input module', () => {
  beforeEach(() => {
    vi.useFakeTimers({ toFake: ['setTimeout', 'clearTimeout', 'Date', 'performance'] });
  });

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

  it('sends committed text after a normal composition cycle', () => {
    const { textarea, sent } = loadCjkHarness();

    textarea.fire('compositionstart');
    textarea.value = PHANTOM + '你好';
    textarea.fire('input', { isComposing: true, inputType: 'insertCompositionText' });
    textarea.fire('compositionend');
    vi.advanceTimersByTime(10);

    expect(sent).toEqual(['你好']);
    expect(textarea.value).toBe(PHANTOM);
  });

  it('recovers committed text when compositionend never fires (stuck composition)', () => {
    const { textarea, sent } = loadCjkHarness();

    // IME fires compositionstart but never compositionend (WeChat/Sogou quirk).
    textarea.fire('compositionstart');
    textarea.value = PHANTOM + '你好';
    // The commit arrives as a plain input event outside composition.
    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
    vi.advanceTimersByTime(200);

    expect(sent).toEqual(['你好']);
  });

  it('does not flush or reset the textarea while the next composition is active', () => {
    const { textarea, sent } = loadCjkHarness();

    // Word 1 commits; the deferred flush is queued but has not run yet.
    textarea.fire('compositionstart');
    textarea.value = PHANTOM + '你好';
    textarea.fire('compositionend');
    // Word 2 composition begins immediately (fast continuous typing).
    textarea.fire('compositionstart');
    textarea.value = PHANTOM + '你好世界';

    // Deferred flush from word 1 fires now — it must NOT touch the textarea
    // (a programmatic reset here cancels the live IME composition on iOS).
    vi.advanceTimersByTime(10);
    expect(sent).toEqual([]);
    expect(textarea.value).toBe(PHANTOM + '你好世界');

    textarea.fire('compositionend');
    vi.advanceTimersByTime(10);
    expect(sent).toEqual(['你好世界']);
  });

  it('does not discard an IME commit landing inside the keydown echo window', () => {
    const { textarea, sent } = loadCjkHarness();

    // English char goes out immediately via keydown.
    textarea.fire('keydown', { key: 'a', ctrlKey: false, altKey: false, metaKey: false });
    expect(sent).toEqual(['a']);

    // Within 100ms the IME commits Chinese via a bare input event.
    vi.advanceTimersByTime(50);
    textarea.value = PHANTOM + '你好';
    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
    vi.advanceTimersByTime(200);

    expect(sent).toEqual(['a', '你好']);
  });

  it('still suppresses the true textarea echo of a keydown-sent character', () => {
    const { textarea, sent } = loadCjkHarness();

    textarea.fire('keydown', { key: 'a', ctrlKey: false, altKey: false, metaKey: false });
    expect(sent).toEqual(['a']);

    // Third-party IME ignored preventDefault — the same char echoes into
    // the textarea. It must be dropped, not sent twice.
    vi.advanceTimersByTime(10);
    textarea.value = PHANTOM + 'a';
    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
    vi.advanceTimersByTime(300);

    expect(sent).toEqual(['a']);
    expect(textarea.value).toBe(PHANTOM);
  });

  it('re-tapping the focused empty field restarts the IME session (wedged-IME recovery)', () => {
    const { textarea, documentObj } = loadCjkHarness();
    documentObj.activeElement = textarea;
    let blurred = 0;
    let focused = 0;
    textarea.blur = () => {
      blurred++;
    };
    textarea.focus = () => {
      focused++;
    };

    textarea.fire('pointerdown');
    expect(blurred).toBe(1);
    vi.advanceTimersByTime(10);
    expect(focused).toBe(1);

    // First tap on an unfocused field must NOT cycle (normal focus flow).
    documentObj.activeElement = null;
    textarea.fire('pointerdown');
    expect(blurred).toBe(1);
  });

  it('skips redundant textarea writes when already reset (Android IME desync guard)', () => {
    const { CjkInput, textarea } = loadCjkHarness();
    const before = textarea.valueWrites;

    // Value is already the phantom — external clears (session switch / SSE
    // reconnect) must not rewrite it, or they race the IME session setup.
    CjkInput.clear();
    CjkInput.clear();

    expect(textarea.valueWrites).toBe(before);
  });

  it('routes terminal.focus() to the CJK field while it is visible (focus router)', () => {
    // Regression guard for the intermittent "Chinese input goes nowhere" bug:
    // session-select / SSE-reconnect paths call terminal.focus(), which lands
    // on xterm's hidden textarea; with the CJK gate active, everything typed
    // there is swallowed. terminal-ui must (a) route focus() to the CJK field
    // when visible and (b) self-heal inside the onData gate.
    const src = readFileSync(resolve(import.meta.dirname, '../src/web/public/terminal-ui.js'), 'utf8');

    expect(src).toContain('Focus router');
    expect(src).toMatch(/this\.terminal\.focus = \(\) => \{/);
    expect(src).toContain("cjkEl?.classList.contains('cjk-input-visible')");
    expect(src).toContain('CJK regain-focus (onData swallowed input)');
  });

  it('sends text plus carriage return on Enter', () => {
    const { textarea, sent } = loadCjkHarness();

    textarea.value = PHANTOM + '你好';
    textarea.fire('keydown', { key: 'Enter' });

    expect(sent).toEqual(['你好\r']);
    expect(textarea.value).toBe(PHANTOM);
  });
});