/**
 * How to reach the local UI from where the admin is sitting. On a machine with a desktop, open
 * the URL; over SSH or on a headless server, forward the port from the admin's own computer
 * first. The UI binds 127.0.0.1 only and checks the Host header, so the local port must equal
 * the remote one.
 */

import { hostname, userInfo } from 'node:os';

/** Over SSH, or Linux with no display server: a browser here would show nothing to the admin. */
export function isHeadless(platform: NodeJS.Platform = process.platform, env: NodeJS.ProcessEnv = process.env): boolean {
  if (env.SSH_CONNECTION || env.SSH_TTY) return true;
  return platform === 'linux' && !env.DISPLAY && !env.WAYLAND_DISPLAY;
}

/** Who to SSH in as, and where; `sshPort` only when it is not 22. */
export interface SshLogin {
  user: string;
  host: string;
  sshPort?: number;
}

/** The lines telling the admin how to open the UI at `port`. */
export function uiAccessLines(port: number, headless: boolean, who: SshLogin = currentLogin()): string[] {
  const url = `http://127.0.0.1:${port}`;
  if (!headless) return [`Open the UI: ${url}`];
  const portFlag = who.sshPort !== undefined && who.sshPort !== 22 ? ` -p ${who.sshPort}` : '';
  return [
    'Open the UI from your own computer (this session has no screen):',
    `  ssh${portFlag} -L ${port}:127.0.0.1:${port} ${who.user}@${who.host}`,
    `  then browse to ${url}`,
  ];
}

/**
 * Over SSH, the server address and port the admin's client connected to (`SSH_CONNECTION` is
 * "client-ip client-port server-ip server-port"): a VPS's hostname rarely resolves from the
 * admin's computer, the address they just reached does. Otherwise this machine's hostname.
 */
export function currentLogin(env: NodeJS.ProcessEnv = process.env): SshLogin {
  let user = '<you>';
  try {
    user = userInfo().username;
  } catch {
    // no passwd entry (some containers): keep the placeholder
  }
  const [, , serverIp, serverPort] = (env.SSH_CONNECTION ?? '').trim().split(/\s+/);
  if (serverIp && serverPort) return { user, host: serverIp, sshPort: Number(serverPort) };
  return { user, host: hostname() };
}