minesweeper/sidecar/session.ts

import type { Subprocess } from 'bun';
import { existsSync, rmSync } from 'node:fs';
import { GAME_EXE, RUN_DIR, VNC_SOCKET, ensureDirs } from './paths';
import { WINE_ENV, confineAndVerify, ensurePrefix, prefixReady } from './prefix';
import { run, waitFor } from './run';

/**
 * The Minesweeper session: a virtual display, one Windows game on it, and x11vnc serving that display over
 * a private unix socket.
 *
 * ── The sidecar owns these processes ──
 *
 * They are spawned as its children, so PM2's tree-kill reaches them and a `pm2 restart officer-minesweeper`
 * genuinely restarts the session. The version this replaced had the PLATFORM spawn a detached shell script:
 * the game outlived every platform restart, nothing supervised it, and a crashed run left wine processes
 * holding the prefix so the next start hung rather than failed. That last one was diagnosed the hard way —
 * four `winedevice` processes survived a stop that reported success.
 *
 * ── Stopping wine properly ──
 *
 * Killing the game is not enough: `wineserver` and `winedevice` outlive it and keep the prefix locked. The
 * script this replaces reached for `pkill -f wineserver`, which would also kill every OTHER wine prefix on
 * the machine — someone's actual application, killed by a game of Minesweeper. `wineserver -k` with
 * `WINEPREFIX` set is the scoped equivalent and is what wine provides for exactly this.
 */

type Proc = Subprocess<'ignore', 'pipe', 'pipe'>;

export type WindowGeometry = { width: number; height: number; x: number; y: number };
export type SessionStatus = {
  /** The game is present and the host has what it needs to run it. */
  installed: boolean;
  running: boolean;
  /** Null until the game has drawn its window. */
  window: WindowGeometry | null;
  /** Set when the last start failed, so the panel can say why instead of showing an empty canvas. */
  error?: string;
};

/**
 * The stage: a fixed framebuffer, with the game centred in it.
 *
 * The game window changes size with the difficulty — 152x214 on beginner, 504x342 on expert, larger
 * again on a custom board — and the whole framebuffer is what gets streamed, so the panel sees one
 * stable rectangle whatever is being played. The alternative, and what this replaced, was parking the
 * window at the origin and having the client crop to its size: that made the panel resize under the
 * player mid-game, and it was wrong by the 3x29 wine puts between the root origin and the window, which
 * showed as a black strip on top and a row of cut-off cells at the bottom.
 *
 * 800x600 is generous on beginner and that is deliberate: it holds the largest board Minesweeper X can
 * make (30x24 custom, 504x470) with room to spare, so no difficulty ever reaches an edge.
 */
const SCREEN_W = 800;
const SCREEN_H = 600;

/**
 * How often to check whether the board changed size.
 *
 * Nothing announces a resize — not RFB, which keeps the framebuffer, and not X without a window manager
 * to listen through. The game only resizes when somebody picks a difficulty, so this is idle almost
 * always; one chained `xdotool` per second is the price of the re-centre feeling immediate when it is
 * not.
 */
const CENTRE_INTERVAL_MS = 1_000;

/** The desktop behind the game. Windows 95's own, because that is what this is a picture of. */
const STAGE_COLOUR = '#008080';

let xvfb: Proc | null = null;
let game: Proc | null = null;
let vnc: Proc | null = null;
let display: string | null = null;
let lastError: string | null = null;
let starting: Promise<SessionStatus> | null = null;

const alive = (p: Proc | null): boolean => !!p && p.exitCode === null && p.signalCode === null;

/**
 * A display number nothing else is using.
 *
 * An X display IS a unix socket at `/tmp/.X11-unix/X<n>`, so this is a real check rather than a guess. The
 * version this replaces hardcoded `:7`, which silently attaches to whatever is already there — including
 * the owner's own session if they happen to run one on that number.
 */
function pickDisplay(): string | null {
  for (let n = 20; n < 100; n++) {
    if (!existsSync(`/tmp/.X11-unix/X${n}`)) return `:${n}`;
  }
  return null;
}

type FoundWindow = WindowGeometry & { id: string };

/**
 * The game's window, with the id needed to move it.
 *
 * wine creates several 1x1 owner stubs under the same name, so the largest candidate is the real one.
 *
 * One `xdotool` process, not one per candidate: `search … getwindowgeometry --shell %@` chains the two
 * commands and prints a block per window. That matters because this now runs on a timer rather than once
 * at startup, and the old shape spawned five processes a tick.
 */
async function findWindow(): Promise<FoundWindow | null> {
  if (!display) return null;
  const found = await run(
    ['xdotool', 'search', '--name', 'Minesweeper X', 'getwindowgeometry', '--shell', '%@'],
    { DISPLAY: display },
    5_000,
  );
  if (!found.ok) return null;

  // WINDOW= opens each block; the keys after it belong to that window until the next one.
  const blocks: Record<string, string>[] = [];
  for (const line of found.stdout.split('\n')) {
    const match = /^(\w+)=(.+)$/.exec(line.trim());
    if (!match) continue;
    const [, key, value] = match;
    if (key === undefined || value === undefined) continue; // the regex guarantees both; the compiler does not
    if (key === 'WINDOW') blocks.push({});
    const block = blocks[blocks.length - 1];
    if (block) block[key] = value;
  }

  let best: FoundWindow | null = null;
  for (const block of blocks) {
    const id = block.WINDOW;
    const candidate = {
      width: Number(block.WIDTH),
      height: Number(block.HEIGHT),
      x: Number(block.X),
      y: Number(block.Y),
    };
    if (!id || Object.values(candidate).some(Number.isNaN)) continue;
    if (!best || candidate.width * candidate.height > best.width * best.height) best = { id, ...candidate };
  }
  return best && best.width > 1 ? best : null;
}

/** The game's window geometry, for `/status`. Nothing in the panel needs it — it is a diagnostic. */
export async function windowGeometry(): Promise<WindowGeometry | null> {
  const found = await findWindow();
  return found ? { width: found.width, height: found.height, x: found.x, y: found.y } : null;
}

/**
 * Put the game in the middle of the stage.
 *
 * Clamped at zero so a board wider or taller than the framebuffer loses its right and bottom edges
 * rather than its menu bar — a negative origin would push the part you need to click off the top.
 */
async function centre(): Promise<void> {
  const win = await findWindow();
  if (!win || !display) return;
  const x = Math.max(0, Math.round((SCREEN_W - win.width) / 2));
  const y = Math.max(0, Math.round((SCREEN_H - win.height) / 2));
  if (win.x === x && win.y === y) return;
  await run(['xdotool', 'windowmove', win.id, String(x), String(y)], { DISPLAY: display }, 5_000);
}

let centring: ReturnType<typeof setTimeout> | null = null;

/**
 * Re-centre whenever the board changes size, for as long as the session is up.
 *
 * Self-scheduling rather than `setInterval`: a tick spawns a process and awaits it, and an interval that
 * fires faster than that completes would stack ticks on a slow machine.
 */
function watchForResize(): void {
  if (centring) return;
  const tick = async () => {
    if (!isRunning()) {
      centring = null;
      return;
    }
    await centre().catch(() => undefined);
    centring = setTimeout(tick, CENTRE_INTERVAL_MS);
  };
  centring = setTimeout(tick, CENTRE_INTERVAL_MS);
}

/**
 * Whether the session is up, decided by the socket file plus a live x11vnc.
 *
 * Deliberately NOT by connecting. An earlier version opened a connection and dropped it, which wedged the
 * server: libvncserver peeks at every new connection to decide whether it is a WebSocket handshake, and
 * that peek blocks its main loop until the client speaks or the peek times out. A health check that
 * connects and says nothing is therefore a small stall — and the panel polls status on a timer, so the
 * stalls overlapped, the accept backlog filled, and the real viewer stopped getting in.
 *
 * The rule that cost: a liveness check must not be indistinguishable from a client.
 */
export const isRunning = (): boolean => alive(vnc) && alive(xvfb) && existsSync(VNC_SOCKET);

export async function status(): Promise<SessionStatus> {
  const installed = existsSync(GAME_EXE) && !!Bun.which('wine') && !!Bun.which('Xvfb') && !!Bun.which('x11vnc');
  const running = isRunning();
  return {
    installed,
    running,
    window: running ? await windowGeometry() : null,
    ...(lastError && !running ? { error: lastError } : {}),
  };
}

const spawn = (cmd: string[], env: Record<string, string>, logName: string): Proc => {
  const proc = Bun.spawn(cmd, { env: { ...process.env, ...env }, stdin: 'ignore', stdout: 'pipe', stderr: 'pipe' });
  // Wine and x11vnc both say useful things only when something is wrong. Prefixed so `pm2 logs
  // officer-minesweeper` shows which process is complaining.
  for (const stream of [proc.stdout, proc.stderr]) {
    void (async () => {
      for await (const chunk of stream as ReadableStream<Uint8Array>) {
        const text = new TextDecoder().decode(chunk).trimEnd();
        if (text) console.log(`[minesweeper:${logName}] ${text}`);
      }
    })().catch(() => {
      /* stream closed with the process */
    });
  }
  return proc as Proc;
};

async function startInner(log: (line: string) => void): Promise<SessionStatus> {
  ensureDirs();
  lastError = null;

  if (!existsSync(GAME_EXE)) {
    lastError = 'the game executable is missing from the plugin directory';
    return status();
  }

  // ── the display ──
  if (!alive(xvfb)) {
    display = pickDisplay();
    if (!display) {
      lastError = 'no free X display number between :20 and :99';
      return status();
    }
    log(`Xvfb on ${display} at ${SCREEN_W}x${SCREEN_H}`);
    // `-nolisten tcp` — the display is reached through its unix socket and has no business on a port.
    xvfb = spawn(['Xvfb', display, '-screen', '0', `${SCREEN_W}x${SCREEN_H}x24`, '-nolisten', 'tcp'], {}, 'xvfb');

    const up = await waitFor(async () => (await run(['xdpyinfo', '-display', display!], {}, 5_000)).ok, 15_000);
    if (!up) {
      lastError = 'the virtual display never became usable';
      await stop();
      return status();
    }
  }

  // The prefix is built HERE, after the display exists and before the game needs it. Not earlier: the VB6
  // installer opens a window, so a prefix built without a display fails in a way that names neither.
  const built = await ensurePrefix(log, display!);
  if (!built.ok) {
    lastError = built.detail;
    await stop();
    return status();
  }

  const env = { ...WINE_ENV, DISPLAY: display! };

  // ── the game ──
  if (!alive(game)) {
    log('launching Minesweeper X under wine');
    game = spawn(['wine', GAME_EXE], env, 'wine');

    const drew = await waitFor(async () => !!(await windowGeometry()), 30_000);
    if (!drew) {
      lastError = 'the game started but never drew a window';
      await stop();
      return status();
    }

    await centre();
  }

  // Wine has now booted the prefix, and booting it is what can restore `Z:`. The confinement in
  // `ensurePrefix` happens before that, so on its own it would be undone by exactly the event it exists to
  // survive. See `confineAndVerify`.
  confineAndVerify(log);

  // ── the display server ──
  if (!alive(vnc)) {
    // A socket left by a crashed run refuses to bind. Removing it is safe: nothing else may write here.
    rmSync(VNC_SOCKET, { force: true });
    log('x11vnc on a private unix socket');
    /*
      `-nopw` with `-unixsock`, and the pair is the whole security argument.

      There is no listening port. The only way in is opening a socket file inside RUN_DIR, which is mode
      0700 and owned by whoever runs this sidecar — so the kernel refuses every other account before
      x11vnc is asked anything. A password would be a second lock on a door only one person can reach, and
      one more secret to store, rotate and leak.

      The version this replaces bound `127.0.0.1:5907` with `-nopw`, which is a different claim entirely:
      every local account could open it and take the display. Survivable on a single-user machine, and not
      once members have Linux accounts. A fixed port is squattable too — anything can bind 5907 first and
      then be relayed to, by the platform, on this plugin's behalf.
    */
    vnc = spawn(
      // -forever: survive a viewer disconnecting. -shared: more than one viewer. -noxdamage: the damage
      // extension reports nothing useful on Xvfb and costs a poll that misses updates.
      //
      // THE THREE PORT FLAGS ARE WHAT MAKE THE PARAGRAPH ABOVE TRUE, AND ALL THREE ARE LOAD-BEARING.
      //
      // `-unixsock` ADDS a unix socket; it does not remove the TCP one. So the first version of this
      // listened on 0.0.0.0:5900 AND [::]:5900 with -nopw, while its own comment said there was no port
      // to authenticate against — anything on the tailnet, anything on the LAN, and every other account
      // on the machine could take the display. Found with `ss -lntp` on the running session. Reading the
      // flags would never have shown it, because the flag that mattered was the one nobody had written.
      //
      // `-rfbport 0` alone leaves `[::]:5900` up; `-rfbportv6 0` is what closes it. Verified by `ss` on
      // the real process both times, which is the only check that has been right about this so far —
      // running the same argv by hand showed no IPv6 listener at all, almost certainly because the
      // session under PM2 was still holding [::]:5900 and the hand-run copy silently failed to bind it.
      //
      // Do not drop one of these because a check looks clean. Check the RUNNING process.
      //
      // -solid: the stage is bigger than the game, so the surround is now something people look at. Teal
      // rather than the root's black, which reads as a broken stream rather than a desktop. x11vnc sets it
      // itself on a bare display, so this costs no new host binary.
      //
      // -nocursor: the browser already draws a cursor over the canvas, and it is the accurate one. The
      // client asks for Raw and CopyRect and nothing else — no cursor pseudo-encoding — so x11vnc has
      // nowhere to send a cursor SHAPE and composites it into the framebuffer instead. That put a second
      // pointer in the picture, lagging the real one by a round trip and, on a bare X server with no
      // window manager, drawn as the big black X of the root cursor. Hiding it server-side is the fix;
      // adding the pseudo-encoding to the client would be a worse one, since the answer is not to draw
      // the remote cursor better but not to draw it at all.
      ['x11vnc', '-display', display!, '-unixsock', VNC_SOCKET, '-rfbport', '0', '-rfbportv6', '0', '-noipv6', '-solid', STAGE_COLOUR, '-nocursor', '-forever', '-shared', '-nopw', '-noxdamage', '-wait', '5', '-defer', '5'],
      { DISPLAY: display! },
      'x11vnc',
    );

    const listening = await waitFor(() => existsSync(VNC_SOCKET), 15_000);
    if (!listening) {
      lastError = 'x11vnc never created its socket';
      await stop();
      return status();
    }
  }

  watchForResize();

  log('ready');
  return status();
}

/** Idempotent, and safe to call concurrently — two panels opening at once must not race two sessions up. */
export function start(log: (line: string) => void): Promise<SessionStatus> {
  if (isRunning()) return status();
  if (starting) return starting;
  starting = startInner(log).finally(() => {
    starting = null;
  });
  return starting;
}

async function reap(proc: Proc | null, name: string): Promise<void> {
  if (!alive(proc)) return;
  proc!.kill('SIGTERM');
  const gone = await waitFor(() => !alive(proc), 3_000, 100);
  if (!gone) {
    console.log(`[minesweeper] ${name} ignored SIGTERM; killing`);
    proc!.kill('SIGKILL');
  }
}

export async function stop(): Promise<SessionStatus> {
  if (centring) {
    clearTimeout(centring);
    centring = null;
  }

  await reap(vnc, 'x11vnc');
  vnc = null;
  rmSync(VNC_SOCKET, { force: true });

  await reap(game, 'wine');
  game = null;

  // Scoped to THIS prefix. `wineserver` and `winedevice` are not our children and outlive the game, holding
  // the prefix so the next start hangs; `-k` is wine's own way to end them, and unlike `pkill -f wineserver`
  // it cannot touch another prefix somebody else is using.
  if (Bun.which('wineserver')) await run(['wineserver', '-k'], WINE_ENV, 10_000).catch(() => undefined);

  await reap(xvfb, 'Xvfb');
  xvfb = null;
  display = null;

  return status();
}

export const runDir = RUN_DIR;
export const prefixIsReady = prefixReady;