// Fingers on the screen, in Chromium and in WebKit alike (plan §7.2, M7): a
// tap through Playwright's touchscreen; a press, a drag and two fingers
// through each engine's own touch input — Chromium's DevTools protocol
// (Input.dispatchTouchEvent), and WebKit's page protocol, whose command has
// the same name and points but which Playwright does not hand out: it is
// reached through the in-process connection (Playwright runs its server in
// the test's process). That seam belongs to Playwright's insides; the
// version is pinned (package.json), and a newer one may move it.

import type { CDPSession, Page } from '@playwright/test';

export interface Point {
  readonly x: number;
  readonly y: number;
}

type TouchType = 'touchStart' | 'touchMove' | 'touchEnd';

export interface Fingers {
  tap(at: Point): Promise<void>;
  /** One finger held where it is, then lifted (a long press: 700 ms). */
  press(at: Point, milliseconds?: number): Promise<void>;
  /** One finger moved from one point to another in steps. */
  drag(from: Point, to: Point, steps?: number): Promise<void>;
  /** Two fingers either side of a middle, moved from one distance apart to another. */
  pinch(middle: Point, from: number, to: number, steps?: number): Promise<void>;
}

interface WebKitSession {
  send(method: string, params: unknown): Promise<unknown>;
}

/** WebKit's page session: Playwright's own object behind the page, its page proxy's session. */
function webKitSession(page: Page): WebKitSession {
  const connection = (page as unknown as { _connection: { toImpl?: (object: unknown) => { delegate?: unknown; _delegate?: unknown } } })._connection;
  const server = connection.toImpl?.(page);
  const delegate = (server?.delegate ?? server?._delegate) as { _pageProxySession?: WebKitSession } | undefined;
  if (delegate?._pageProxySession === undefined) throw new Error("WebKit's page session is out of reach: Playwright's insides have changed");
  return delegate._pageProxySession;
}

export async function fingers(page: Page): Promise<Fingers> {
  const engine = page.context().browser()?.browserType().name();
  let send: (type: TouchType, points: readonly Point[]) => Promise<unknown>;
  if (engine === 'webkit') {
    const session = webKitSession(page);
    // WebKit ends a touch with the fingers lifted, not with none.
    let last: readonly Point[] = [];
    send = (type, points) => {
      const touched = type === 'touchEnd' ? last : points;
      if (type !== 'touchEnd') last = points;
      return session.send('Input.dispatchTouchEvent', { type, touchPoints: touched.map(({ x, y }, id) => ({ x: Math.round(x), y: Math.round(y), id })) });
    };
  } else {
    const cdp: CDPSession = await page.context().newCDPSession(page);
    send = (type, points) => cdp.send('Input.dispatchTouchEvent', { type, touchPoints: points.map(({ x, y }, id) => ({ x, y, id })) });
  }
  const steps = (count: number) => Array.from({ length: count }, (_, index) => (index + 1) / count);
  return {
    tap: (at) => page.touchscreen.tap(at.x, at.y),
    async press(at, milliseconds = 700) {
      await send('touchStart', [at]);
      await page.waitForTimeout(milliseconds);
      await send('touchEnd', []);
    },
    async drag(from, to, count = 8) {
      await send('touchStart', [from]);
      for (const share of steps(count)) await send('touchMove', [{ x: from.x + (to.x - from.x) * share, y: from.y + (to.y - from.y) * share }]);
      // Held still before it is lifted, as a finger that puts something down: lifted on the move, Chromium
      // takes it for a fling, and the next tap only stops the fling (no click).
      await page.waitForTimeout(150);
      await send('touchEnd', []);
    },
    async pinch(middle, from, to, count = 4) {
      const pair = (distance: number): Point[] => [
        { x: middle.x - distance, y: middle.y },
        { x: middle.x + distance, y: middle.y },
      ];
      await send('touchStart', pair(from));
      for (const share of steps(count)) await send('touchMove', pair(from + (to - from) * share));
      await page.waitForTimeout(150);
      await send('touchEnd', []);
    },
  };
}