/**
 * @file pty-attach.js
 * @description Bridges one WebSocket connection to a `node-pty`-backed
 * `tmux attach-session` process. Binary WS frames carry raw PTY bytes in
 * both directions; text WS frames carry small JSON control messages
 * (`resize`, and an outbound `exit` sent once when the pane process/tmux
 * session ends). Multiple browser tabs each get their own PTY attach
 * process — tmux itself is what keeps them all in sync, this module does no
 * cross-connection coordination.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

const RUN_ID_RE = /^ccam-lane-\d+$/;

/**
 * Reject anything that isn't exactly `ccam-lane-<digits>` before it can ever
 * reach a tmux/PTY command — the trust boundary for this WS path, since a
 * validated runId is the only thing standing between an authenticated WS
 * client and naming an arbitrary session on the host.
 */
function validateRunId(runId) {
  if (typeof runId !== "string" || !RUN_ID_RE.test(runId)) {
    const err = new Error(`EBADRUNID: invalid runId: ${runId}`);
    err.code = "EBADRUNID";
    throw err;
  }
}

// Test seam — real implementation set in Step 4.
let spawnImpl = null;
function __setSpawnImpl(fn) {
  spawnImpl = fn;
}

/**
 * Attach `ws` to the tmux session `runId`. Spawns one PTY-backed
 * `tmux attach-session -t <runId>` per call.
 */
function attach(ws, runId, { cols, rows }) {
  validateRunId(runId);
  const pty = spawnImpl("tmux", ["attach-session", "-t", runId], {
    name: "xterm-256color",
    cols: cols || 80,
    rows: rows || 24,
  });

  pty.onData((data) => {
    try {
      ws.send(data, { binary: true });
    } catch {
      /* client gone between data event and send — safe to ignore */
    }
  });

  pty.onExit(({ exitCode }) => {
    try {
      ws.send(JSON.stringify({ type: "exit", code: exitCode }), { binary: false });
    } catch {
      /* ignore */
    }
    try {
      ws.close();
    } catch {
      /* ignore */
    }
  });

  ws.on("message", (data, isBinary) => {
    // node-pty attach processes for `tmux attach` are already tolerant of
    // resize mid-stream; the `ws` lib passes isBinary either as the second
    // callback arg (newer) or via `data.binary` on some transports — this
    // helper's own tests exercise the `{binary}` option shape used above.
    const binary = typeof isBinary === "boolean" ? isBinary : !!(isBinary && isBinary.binary);
    if (binary) {
      pty.write(data.toString("utf8"));
      return;
    }
    let msg;
    try {
      msg = JSON.parse(data.toString("utf8"));
    } catch {
      return;
    }
    if (msg && msg.type === "resize" && Number.isFinite(msg.cols) && Number.isFinite(msg.rows)) {
      pty.resize(msg.cols, msg.rows);
    }
  });

  ws.on("close", () => {
    try {
      pty.kill();
    } catch {
      /* already gone */
    }
  });

  return pty;
}

// Real spawn implementation — lazy-required so unit tests never load the
// native node-pty addon unless they explicitly opt in.
__setSpawnImpl((...args) => require("node-pty").spawn(...args));

module.exports = { attach, validateRunId, __setSpawnImpl };