/**
 * tmux session manager.
 *
 * Spawn, list, kill sessions and read metadata stored via tmux @description
 * option. Checks tmux version at startup (requires >= 2.5).
 *
 * Owner: T-1.1
 */

import { execFile } from "node:child_process";
import { promisify } from "node:util";

const execFileAsync = promisify(execFile);

export interface TmuxSession {
  id: string; // tmux session name (used as our ID)
  name: string; // human name (same as id for now; T-1.4 may rename via @description)
  description?: string; // from tmux @description option
  createdAt: string; // ISO string, from tmux session_created_string
  lastActivityAt: string; // ISO string, from tmux session_last_attached
  width: number;
  height: number;
}

// ---------------------------------------------------------------------------
// Version guard
// ---------------------------------------------------------------------------

let versionChecked = false;

export async function checkTmuxVersion(): Promise<void> {
  if (versionChecked) return;
  const { stdout } = await execFileAsync("tmux", ["-V"]);
  const match = stdout.trim().match(/tmux (\d+)\.(\d+)/);
  if (!match) throw new Error(`Cannot parse tmux version: ${stdout.trim()}`);
  const major = parseInt(match[1], 10);
  const minor = parseInt(match[2], 10);
  if (major < 2 || (major === 2 && minor < 5)) {
    throw new Error(
      `tmux >= 2.5 required (found ${stdout.trim()}). Upgrade tmux to use pi-remote-control.`,
    );
  }
  versionChecked = true;
}

// ---------------------------------------------------------------------------
// Session CRUD
// ---------------------------------------------------------------------------

/**
 * Spawn a new detached tmux session.
 * Returns the session name (used as stable ID).
 */
export async function spawnSession(opts: {
  name: string;
  width?: number;
  height?: number;
  command?: string;
}): Promise<string> {
  await checkTmuxVersion();
  const { name, width = 120, height = 40, command = "" } = opts;

  const args = [
    "new-session",
    "-d",
    "-s",
    name,
    "-x",
    String(width),
    "-y",
    String(height),
  ];
  if (command) args.push(command);

  await execFileAsync("tmux", args);
  return name;
}

/**
 * List all tmux sessions with metadata.
 */
export async function listSessions(): Promise<TmuxSession[]> {
  await checkTmuxVersion();

  // Use a separator that's unlikely to appear in session names
  const SEP = "\x1F"; // ASCII unit separator
  const fmt = [
    "#{session_name}",
    "#{session_created_string}",
    "#{session_last_attached_string}",
    "#{window_width}",
    "#{window_height}",
  ].join(SEP);

  let stdout: string;
  try {
    ({ stdout } = await execFileAsync("tmux", ["list-sessions", "-F", fmt]));
  } catch (err: unknown) {
    // tmux exits 1 when no sessions exist
    if (
      err &&
      typeof err === "object" &&
      "code" in err &&
      (err as { code: number }).code === 1
    ) {
      return [];
    }
    throw err;
  }

  const sessions: TmuxSession[] = [];
  for (const line of stdout.trim().split("\n")) {
    if (!line) continue;
    const [id, createdAt, lastActivityAt, w, h] = line.split(SEP);

    // Fetch @description option separately (may not be set)
    let description: string | undefined;
    try {
      const r = await execFileAsync("tmux", [
        "show-options",
        "-t",
        id,
        "-qv",
        "@description",
      ]);
      const v = r.stdout.trim();
      if (v) description = v;
    } catch {
      // option not set — that's fine
    }

    sessions.push({
      id,
      name: id,
      description,
      createdAt,
      lastActivityAt,
      width: parseInt(w, 10) || 120,
      height: parseInt(h, 10) || 40,
    });
  }
  return sessions;
}

/**
 * Get a single session by name. Returns null if not found.
 */
export async function getSession(name: string): Promise<TmuxSession | null> {
  const all = await listSessions();
  return all.find((s) => s.id === name) ?? null;
}

/**
 * Kill a session. Throws if it doesn't exist.
 */
export async function killSession(name: string): Promise<void> {
  await checkTmuxVersion();
  await execFileAsync("tmux", ["kill-session", "-t", name]);
}

/**
 * Set the @description option on a session.
 */
export async function setDescription(
  name: string,
  description: string,
): Promise<void> {
  await execFileAsync("tmux", [
    "set-option",
    "-t",
    name,
    "@description",
    description,
  ]);
}