import { existsSync } from 'node:fs';
import { runAs } from './os-user';

// A member's own Docker: their daemon, their images, their containers, running as their uid.
//
// ── Why rootless, and why the alternative is not on the table ──
//
// The one-line version of "give the user Docker" is `usermod -aG docker <user>`, and it is root. Membership of
// that group means talking to the host daemon, which runs as root, so:
//
//   docker run -v /:/host -it alpine chroot /host
//
// is a root shell on the machine. It reads the platform's `.env`, every other member's home, the wallet seed
// — every boundary in docs/per-user-linux-accounts.md, bypassed by one documented command. The group is not
// "access to Docker", it is "root, by a longer route".
//
// Rootless gives the thing that was actually wanted: a daemon per account, containers in that account's user
// namespace, images in their own home. Root inside their container is their uid outside it, which is nobody.
// They cannot see the owner's containers and the owner cannot break theirs.
//
// ── What it needs from the host ──
//
//   uidmap             newuidmap/newgidmap, to map subordinate ids. Rootless cannot start without them.
//   /etc/subuid,gid    a range per account. `useradd` allocates one automatically wherever login.defs sets
//                      SUB_UID_COUNT (Ubuntu does), and `userdel` reclaims it — verified on this host.
//   linger             `loginctl enable-linger`, or the daemon dies with the session. Officer's shells are
//                      NOT login sessions, so without this a member's Docker would stop the moment their
//                      terminal closed, which is the opposite of a daemon.
//   dbus-user-session  systemd --user needs a bus to talk to.
//
// ── The costs, stated rather than discovered ──
//
// Each account has its own image cache, so three members pulling postgres:16 store it three times. Ports
// below 1024 need an explicit capability grant. Both are acceptable for what this buys; neither is hidden.

/** Their own daemon's socket. The value `DOCKER_HOST` must point at. */
export const dockerSocketFor = (uid: number): string => `/run/user/${uid}/docker.sock`;

type Result = { ok: true; alreadyInstalled: boolean } | { ok: false; error: string };

async function sudo(args: string[]): Promise<{ ok: boolean; out: string }> {
  const proc = Bun.spawn(['sudo', '-n', ...args], { stdout: 'pipe', stderr: 'pipe' });
  const [out, err] = await Promise.all([new Response(proc.stdout).text(), new Response(proc.stderr).text()]);
  return { ok: (await proc.exited) === 0, out: `${out}${err}`.trim() };
}

/**
 * Run something as the member with a systemd user session in scope.
 *
 * `runAs` clears the environment, which is right everywhere else and fatal here: `systemctl --user` and the
 * rootless setup tool locate the user manager through `XDG_RUNTIME_DIR` and `DBUS_SESSION_BUS_ADDRESS`. With
 * those unset the tool reports "systemd not detected" and installs nothing, successfully.
 */
function asMemberWithSession(osUser: string, uid: number, command: string[]) {
  const runtime = `/run/user/${uid}`;
  return runAs(osUser, [
    'env',
    `XDG_RUNTIME_DIR=${runtime}`,
    `DBUS_SESSION_BUS_ADDRESS=unix:path=${runtime}/bus`,
    // The tool shells out to newuidmap, rootlesskit and dockerd, and --reset-env left PATH at the passwd
    // default which does not include /usr/sbin.
    'PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
    ...command,
  ]);
}

const text = async (proc: ReturnType<typeof runAs>) =>
  `${await new Response(proc.stdout).text()}${await new Response(proc.stderr).text()}`.trim();

/** Everything that must be true of the HOST before any account can have rootless Docker. */
export function checkDockerPrerequisites(): { ok: true } | { ok: false; error: string } {
  const missing: string[] = [];
  if (!existsSync('/usr/bin/newuidmap') || !existsSync('/usr/bin/newgidmap')) missing.push('uidmap');
  if (!existsSync('/usr/bin/dockerd-rootless-setuptool.sh')) missing.push('docker-ce-rootless-extras');
  if (missing.length) {
    return {
      ok: false,
      error: `rootless Docker needs these packages on the host: ${missing.join(', ')} (apt install ${missing.join(' ')})`,
    };
  }
  return { ok: true };
}

/**
 * Give the account its own rootless Docker daemon, and start it.
 *
 * Idempotent: the setup tool is safe to re-run, `enable-linger` on a lingering account is a no-op, and an
 * already-running daemon is reported as `alreadyInstalled` rather than restarted — a reprovision must not
 * bounce a member's containers.
 *
 * Never throws. Docker is the least essential of the provisioning steps: without it the account still has a
 * shell, a home and keys.
 */
export async function provisionRootlessDocker(params: { osUser: string; uid: number; home: string }): Promise<Result> {
  const prereq = checkDockerPrerequisites();
  if (!prereq.ok) return prereq;

  // Subordinate id range. `useradd` allocates one, so a missing entry means either an unusual login.defs or
  // an account made by hand — worth naming rather than letting rootlesskit fail obscurely later.
  const subuid = await sudo(['grep', '-q', `^${params.osUser}:`, '/etc/subuid']);
  if (!subuid.ok) {
    return {
      ok: false,
      error: `${params.osUser} has no /etc/subuid range, which rootless Docker requires. Add one with: sudo usermod --add-subuids 100000-165535 ${params.osUser}`,
    };
  }

  // Linger FIRST: it is what creates /run/user/<uid> and starts the user manager, and everything below needs
  // both to exist.
  const linger = await sudo(['loginctl', 'enable-linger', params.osUser]);
  if (!linger.ok) return { ok: false, error: `could not enable linger for ${params.osUser}: ${linger.out}` };

  // The user manager appears asynchronously. Waiting beats a bare sleep, and the failure below is clearer
  // than "systemd not detected" from the setup tool.
  for (let attempt = 0; attempt < 25 && !existsSync(`/run/user/${params.uid}`); attempt++) {
    await Bun.sleep(200);
  }
  if (!existsSync(`/run/user/${params.uid}`)) {
    return {
      ok: false,
      error: `/run/user/${params.uid} never appeared, so ${params.osUser} has no systemd user session`,
    };
  }

  const already = existsSync(dockerSocketFor(params.uid));

  // Docker's storage, created by us and created CLEAN, before the daemon exists to create it dirty.
  //
  // The strip below used to be the whole story, guarded on the directory existing — which is false on a first
  // run, because only the daemon creates it. So on a fresh account the strip no-opped, the daemon then made
  // the directory itself and inherited the home's default ACLs, and the only cure was a retry: the very run
  // that was supposed to clean it up was the one that created it. Verified on green's first provision, where
  // it came out carrying `default:other::---` after a "successful" strip.
  //
  // A guard that depends on another process having got there first is a race however it is written, so the
  // fix is ownership of the order: make it ourselves, with the member's uid and no defaults to inherit. Same
  // shape as creating `~/.local` explicitly rather than letting `install -d` invent it as root.
  const dockerStorage = `${params.home}/.local/share/docker`;
  const madeStorage = await sudo([
    'install',
    '-d',
    '-o',
    String(params.uid),
    '-g',
    String(params.uid),
    '-m',
    '700',
    dockerStorage,
  ]);
  if (!madeStorage.ok) {
    return { ok: false, error: `could not create ${dockerStorage}: ${madeStorage.out}` };
  }

  // ── The setup tool's exit code is deliberately NOT the gate ──
  //
  // It writes `~/.config/systemd/user/docker.service` and then runs `systemctl --user start docker.service`
  // itself — which fails with "Unit docker.service not found" on a manager that was already running when the
  // file appeared, because nothing reloaded it. Measured here: the unit was written correctly and the tool
  // still exited 1.
  //
  // So: run it, reload, and start it ourselves. The tool's output is kept for the error message if the start
  // then genuinely fails, since its diagnosis (a missing kernel module, an unsupported filesystem) is better
  // than anything paraphrased.
  const install = asMemberWithSession(params.osUser, params.uid, ['dockerd-rootless-setuptool.sh', 'install']);
  const installOut = await text(install);
  await install.exited;

  const reload = asMemberWithSession(params.osUser, params.uid, ['systemctl', '--user', 'daemon-reload']);
  await reload.exited;

  const enable = asMemberWithSession(params.osUser, params.uid, ['systemctl', '--user', 'enable', '--now', 'docker']);
  const enableOut = await text(enable);
  if ((await enable.exited) !== 0) {
    // Both halves, because the useful sentence is usually in the setup tool's output rather than systemd's.
    const detail = [installOut, enableOut]
      .map((s) => s.split('\n').slice(-3).join(' ').trim())
      .filter(Boolean)
      .join(' | ');
    return { ok: false, error: `could not start ${params.osUser}'s Docker: ${detail}` };
  }

  // ── Undo our own ACLs, for this one subtree ──
  //
  // The home carries DEFAULT ACLs so the file browser can read a member's files (os-user.ts explains why).
  // Docker inherits them under `~/.local/share/docker`, then fails every `docker run` with:
  //
  //   failed to copy xattrs: failed to set xattr "system.posix_acl_default" on …/volumes/…/_data:
  //   invalid argument
  //
  // Creating a volume copies xattrs, and inside a rootless user namespace the mapped id in an inherited
  // default ACL is not a valid id, so setting it is EINVAL. Two features built the same day, each correct
  // alone. Measured: the image pulled fine — 403 MB into their home — and every container failed to start.
  //
  // `-k` removes DEFAULT entries only, so nothing inside Docker's storage inherits them from here on. The
  // access ACLs on the home itself are untouched, which is what the file browser depends on. Losing the
  // platform's reach into Docker's internal storage is no loss: it is image layers and volume data, read
  // through `docker` or not at all.
  // Unconditional now, and no longer the thing that has to win a race: the directory is ours from above, so
  // this is repair for an account provisioned before that existed, and a no-op on a clean one. The guard it
  // replaces could not tell "nothing to strip" from "nothing there yet", and answered the same way to both.
  const stripped = await sudo(['setfacl', '-R', '-k', dockerStorage]);
  if (!stripped.ok) {
    return { ok: false, error: `could not clear inherited ACLs from ${dockerStorage}: ${stripped.out}` };
  }

  // Proof, not assumption: ask their daemon who it is. `docker version --format` on the SERVER half only
  // answers if the socket is live and talking.
  const verify = asMemberWithSession(params.osUser, params.uid, [
    'env',
    `DOCKER_HOST=unix://${dockerSocketFor(params.uid)}`,
    'docker',
    'version',
    '--format',
    '{{.Server.Version}}',
  ]);
  const version = await text(verify);
  if ((await verify.exited) !== 0) {
    return {
      ok: false,
      error: `${params.osUser}'s Docker did not answer: ${version.split('\n').slice(-2).join(' ').trim()}`,
    };
  }

  return { ok: true, alreadyInstalled: already };
}