// Engine launch, cohort observation and force stop (#1507, CHAT-03 §6).
//
// ScopeLauncher starts the supervisor shim (shim.mjs) in a delegated
// systemd user scope named after the claim. The cohort is the scope's
// `engine` cgroup, and the scope's invocation ID is the membership epoch. A
// unit with the right name but another invocation ID is a different cohort:
// it gets no signal, and its evidence is unavailable.
//
// PgroupLauncher is the fallback with no scope: the engine leads its own
// process group. A process group can't be enumerated completely, so a force
// stop on it always ends `uncertain`.
//
// Force stop: check the invocation ID against systemd and the shim; TERM
// every member and wait a bounded grace; freeze `engine` and wait for
// `frozen 1`; enumerate every member with pid and start time; write
// `cgroup.kill`; wait for `populated 0`. Only when all of that succeeded is
// membership complete. Anything unavailable ends the stop `uncertain`. The
// scope stays up after the stop either way; `releaseCohort` ends it once the
// controller has recorded a proven stop.
//
// Engine exit (row 52): at EOF the controller reads the cohort without
// signalling it. The shim reports the engine's PID, start ticks and reap time
// from its wait; `engine` empty with that engine reaped is the proof.

import { spawn, spawnSync } from "node:child_process";
import { existsSync, readFileSync } from "node:fs";
import { connect } from "node:net";
import { dirname, join } from "node:path";
import { fileURLToPath } from "node:url";
import { processStart } from "../../discord/src/journal.mjs";
import { LineSplitter, encodeLine, parseLine } from "./framing.mjs";
import { hash, newId, record, sealProof } from "./records.mjs";

export const AUTHORITY = "mosaic-conversation-shim-fixture";
export const SHIM_PATH = join(dirname(fileURLToPath(import.meta.url)), "shim.mjs");

const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

export function cohortRefOf({ machineId, bootId, unitName, invocationId }) {
  return "cohort-" + hash({ machineId, bootId, unitName, invocationId }).slice(0, 40);
}

// One request per connection keeps a dead shim from wedging a caller.
export function shimRequest(socketPath, op, extra = {}, timeoutMs = 3000) {
  return new Promise((resolve) => {
    if (!socketPath || !existsSync(socketPath)) return resolve({ ok: false, unavailable: "the shim socket is gone" });
    const sock = connect(socketPath);
    let done = false;
    const finish = (v) => {
      if (done) return;
      done = true;
      clearTimeout(timer);
      sock.destroy();
      resolve(v);
    };
    const timer = setTimeout(() => finish({ ok: false, unavailable: `the shim did not answer ${op}` }), timeoutMs);
    const splitter = new LineSplitter((line) => {
      const p = parseLine(line);
      finish(p.error ? { ok: false, unavailable: `shim answer ${p.error}` } : p.value);
    });
    sock.on("data", (c) => splitter.push(c));
    sock.on("error", () => finish({ ok: false, unavailable: "the shim is unreachable" }));
    sock.on("close", () => finish({ ok: false, unavailable: "the shim closed the connection" }));
    sock.on("connect", () => sock.write(encodeLine({ id: 1, op, ...extra })));
  });
}

export function systemctlShow(unitName) {
  const r = spawnSync("systemctl", ["--user", "show", "-p", "LoadState,ActiveState,InvocationID,ControlGroup", `${unitName}.scope`], { encoding: "utf8", timeout: 5000 });
  if (r.status !== 0) return null;
  const out = {};
  for (const line of r.stdout.split("\n")) {
    const i = line.indexOf("=");
    if (i > 0) out[line.slice(0, i)] = line.slice(i + 1);
  }
  return { loadState: out.LoadState ?? null, activeState: out.ActiveState ?? null, invocationId: out.InvocationID || null, controlGroup: out.ControlGroup || null };
}

// claim.classify's unit lookup. A unit systemd has collected is absent; one
// that is loaded and active is alive; anything unreadable is unknown.
export const systemdUnits = Object.freeze({
  lookup(rec) {
    if (!rec?.unitName) return { state: "unknown" };
    const s = systemctlShow(rec.unitName);
    if (!s) return { state: "unknown" };
    if (s.loadState === "not-found" || (s.activeState === "inactive" && !s.controlGroup)) return { state: "absent" };
    if (["active", "activating", "deactivating", "reloading"].includes(s.activeState)) return { state: "alive", invocationId: s.invocationId };
    return { state: "unknown", detail: s };
  },
});

export function scopeAvailable() {
  const r = spawnSync("systemd-run", ["--user", "--scope", "--quiet", "-p", "Delegate=yes", "--", "true"], { timeout: 10000 });
  return r.status === 0;
}

export class ScopeLauncher {
  constructor({ shimPath = SHIM_PATH, startTimeoutMs = 10000 } = {}) {
    this.kind = "scope";
    this.shimPath = shimPath;
    this.startTimeoutMs = startTimeoutMs;
  }

  // systemd-run --user reaches the user manager through these two; a scope's
  // command inherits systemd-run's environment, so the engine sees them too.
  // Neither loads code.
  static MANAGER_ENV = Object.freeze(["XDG_RUNTIME_DIR", "DBUS_SESSION_BUS_ADDRESS"]);

  async launch({ unitName, socketPath, command, args, cwd, env }) {
    const manager = Object.fromEntries(ScopeLauncher.MANAGER_ENV.filter((k) => typeof process.env[k] === "string").map((k) => [k, process.env[k]]));
    const proc = spawn("systemd-run", ["--user", "--scope", "-p", "Delegate=yes", `--unit=${unitName}`, "--quiet", "--", process.execPath, this.shimPath, "--socket", socketPath, "--", command, ...args], {
      cwd, env: { ...manager, ...env }, stdio: ["pipe", "pipe", "pipe"],
    });
    const exited = new Promise((r) => proc.on("exit", (code, signal) => r({ code, signal })));
    const end = Date.now() + this.startTimeoutMs;
    let hello = null;
    while (Date.now() < end) {
      const race = await Promise.race([exited.then((e) => ({ exited: e })), sleep(20).then(() => null)]);
      if (race?.exited) throw Object.assign(new Error(`the scope exited before the shim answered (${JSON.stringify(race.exited)})`), { code: "launch-failed" });
      if (existsSync(socketPath)) {
        hello = await shimRequest(socketPath, "hello");
        if (hello.ok) break;
      }
    }
    if (!hello?.ok) throw Object.assign(new Error("the shim never answered"), { code: "launch-failed", proc });
    const show = systemctlShow(unitName);
    return {
      kind: "scope", proc, stdin: proc.stdin, stdout: proc.stdout, stderr: proc.stderr,
      pid: hello.enginePid, start: hello.engineStart === null ? null : String(hello.engineStart),
      invocationId: hello.invocationId, scope: hello.scope, shimSocket: socketPath,
      systemd: show, exited,
    };
  }
}

export class PgroupLauncher {
  constructor() {
    this.kind = "pgroup";
  }

  async launch({ command, args, cwd, env }) {
    const proc = spawn(command, args, { cwd, env, stdio: ["pipe", "pipe", "pipe"], detached: true });
    const exited = new Promise((r) => proc.on("exit", (code, signal) => r({ code, signal })));
    await new Promise((resolve, reject) => {
      proc.once("spawn", resolve);
      proc.once("error", reject);
    });
    return { kind: "pgroup", proc, stdin: proc.stdin, stdout: proc.stdout, stderr: proc.stderr, pid: proc.pid, start: processStart(proc.pid), invocationId: null, scope: null, shimSocket: null, exited };
  }
}

// Runs the force-stop escalation from the TERM phase. `onPhase(name)` is
// awaited before each phase begins, so the caller records the phase before
// any signal. Returns { outcome: "proven" | "unavailable", ... }. Nothing is
// recorded as done unless it was observed.
export async function forceStopCohort({ kind, unitName, invocationId, shimSocket, pid, graceMs = 1000, onPhase = async () => {} }) {
  if (kind === "pgroup") {
    await onPhase("term");
    try {
      process.kill(-pid, "SIGTERM");
    } catch {
      // the group is gone
    }
    await sleep(graceMs);
    await onPhase("kill");
    try {
      process.kill(-pid, "SIGKILL");
    } catch {
      // the group is gone
    }
    return { outcome: "unavailable", reason: "process-group fallback: membership can't be enumerated completely" };
  }
  const show = systemctlShow(unitName);
  if (!show || !invocationId || show.invocationId !== invocationId) {
    return { outcome: "unavailable", reason: `invocation ID mismatch or unreadable (recorded ${invocationId}, found ${show?.invocationId ?? "none"}); no signal sent` };
  }
  const hello = await shimRequest(shimSocket, "hello");
  if (!hello.ok) return { outcome: "unavailable", reason: hello.unavailable };
  if (hello.invocationId !== invocationId || hello.scope !== show.controlGroup) {
    return { outcome: "unavailable", reason: "the shim does not answer for the recorded scope; no signal sent" };
  }
  await onPhase("term");
  const term = await shimRequest(shimSocket, "term");
  if (!term.ok) return { outcome: "unavailable", reason: term.unavailable, phase: "term" };
  const end = Date.now() + graceMs;
  for (;;) {
    const e = await shimRequest(shimSocket, "events");
    if (!e.ok) return { outcome: "unavailable", reason: e.unavailable, phase: "term" };
    if (e.populated === 0 || Date.now() >= end) break;
    await sleep(20);
  }
  await onPhase("kill");
  const frozen = await shimRequest(shimSocket, "freeze", { timeoutMs: 3000 }, 6000);
  if (!frozen.ok) return { outcome: "unavailable", reason: frozen.unavailable, phase: "kill" };
  if (frozen.timedOut) return { outcome: "unavailable", reason: "engine never reported frozen 1", phase: "kill" };
  const listed = await shimRequest(shimSocket, "members");
  if (!listed.ok) return { outcome: "unavailable", reason: listed.unavailable, phase: "kill" };
  const killed = await shimRequest(shimSocket, "kill", { timeoutMs: 5000 }, 8000);
  if (!killed.ok) return { outcome: "unavailable", reason: killed.unavailable, phase: "kill" };
  if (killed.timedOut || killed.populated !== 0) return { outcome: "unavailable", reason: "engine never reported populated 0", phase: "kill" };
  const observedAt = new Date().toISOString();
  if (listed.members.some((m) => !Number.isInteger(m.startTicks) || m.startTicks < 1)) {
    return { outcome: "unavailable", reason: "a member's start time was unreadable at enumeration", phase: "kill" };
  }
  return {
    outcome: "proven", membershipComplete: true, epoch: invocationId, observedAt, boot: listed.boot,
    members: listed.members.map((m) => ({ pid: m.pid, boot: listed.boot, startTicks: m.startTicks, terminatedAt: observedAt })),
  };
}

// Observes an engine that exited on its own (row 52, CHAT-01 `engine-exit`).
// It reads only: `hello`, `events` and `members`; nothing is frozen or
// signalled. The cohort is proven ended when the shim has reaped the recorded
// engine (its PID and start ticks) and `engine` reads `populated 0` with no
// member listed. The proof's one member is the engine, dead at the shim's
// wait; an empty list is never the proof. EOF can come before the reap, so it
// reads again until `settleMs` pass. Anything else is `unavailable`. The
// caller bounds the whole observation with its own deadline.
export async function engineExitCohort({ kind, unitName, invocationId, shimSocket, pid, start, settleMs = 2000 }) {
  if (kind !== "scope") return { outcome: "unavailable", reason: `a ${kind} cohort can't be enumerated completely` };
  const show = systemctlShow(unitName);
  if (!show || !invocationId || show.invocationId !== invocationId) {
    return { outcome: "unavailable", reason: `invocation ID mismatch or unreadable (recorded ${invocationId}, found ${show?.invocationId ?? "none"})` };
  }
  const end = Date.now() + settleMs;
  for (;;) {
    const hello = await shimRequest(shimSocket, "hello");
    if (!hello.ok) return { outcome: "unavailable", reason: hello.unavailable };
    if (hello.invocationId !== invocationId || hello.scope !== show.controlGroup) return { outcome: "unavailable", reason: "the shim does not answer for the recorded scope" };
    const exit = hello.engineExit;
    if (exit) {
      if (exit.pid !== pid || !Number.isInteger(exit.startTicks) || exit.startTicks < 1 || String(exit.startTicks) !== String(start) || exit.boot !== hello.boot) {
        return { outcome: "unavailable", reason: "the shim reaped a process that isn't the recorded engine" };
      }
      const e = await shimRequest(shimSocket, "events");
      if (!e.ok) return { outcome: "unavailable", reason: e.unavailable };
      if (e.populated === 0) {
        const listed = await shimRequest(shimSocket, "members");
        if (!listed.ok) return { outcome: "unavailable", reason: listed.unavailable };
        if (listed.members.length === 0) {
          return {
            outcome: "proven", membershipComplete: true, epoch: invocationId, observedAt: new Date().toISOString(), boot: hello.boot,
            members: [{ pid, boot: exit.boot, startTicks: exit.startTicks, terminatedAt: exit.at }],
          };
        }
      }
    }
    if (Date.now() >= end) return { outcome: "unavailable", reason: exit ? "the engine cgroup still has a member" : "the shim has not reaped the engine" };
    await sleep(20);
  }
}

// Ends a scope whose cohort is proven stopped (#1536). The shim exits on
// `release` only while `engine` reads `populated 0`, and systemd then
// collects the empty scope. Call it only after a `proven` stop whose claim
// is recorded `stopped`: after an `unavailable` one, the scope and its shim
// are the evidence a later stop reads, and a collected scope is an absent
// observation, never proof. Returns { outcome: "released" | "unavailable",
// ... }; `unit` is `absent` once systemd no longer lists the scope.
export async function releaseCohort({ kind, unitName, invocationId, shimSocket, waitMs = 3000 }) {
  if (kind !== "scope") return { outcome: "unavailable", reason: `a ${kind} cohort has no scope to release` };
  const hello = await shimRequest(shimSocket, "hello");
  if (!hello.ok) return { outcome: "unavailable", reason: hello.unavailable };
  if (!invocationId || hello.invocationId !== invocationId) return { outcome: "unavailable", reason: "the shim does not answer for the recorded scope; nothing released" };
  const released = await shimRequest(shimSocket, "release");
  if (!released.ok) return { outcome: "unavailable", reason: released.unavailable };
  const end = Date.now() + waitMs;
  for (;;) {
    if (systemdUnits.lookup({ unitName }).state === "absent") return { outcome: "released", unit: "absent" };
    if (Date.now() >= end) return { outcome: "released", unit: "still listed" };
    await sleep(20);
  }
}

export function cohortProof({ binding, stop, result }) {
  return sealProof(record("cohortProof", {
    id: newId("cohort-proof"), authority: AUTHORITY, conversation: binding.scope.conversation, execution: binding.execution,
    cohortRef: binding.cohortRef, membershipEpoch: result.epoch, membershipComplete: result.membershipComplete === true,
    members: result.members, observedAt: result.observedAt, verificationDigest: "", stop,
  }));
}

// A tool-start with no tool-end at stop time is an `uncertain` effect.
// Killing never counts as rollback.
export function effectReport({ binding, stop, tools, observedAt }) {
  return sealProof(record("effectReport", {
    id: newId("effects"), authority: AUTHORITY, conversation: binding.scope.conversation, execution: binding.execution,
    cohortRef: binding.cohortRef,
    invocations: [...tools.values()].map((t) => ({ id: t.call, disposition: t.end ? "completed" : "uncertain", evidence: t.end ?? t.start })),
    observedAt, verificationDigest: "", stop,
  }));
}

// The current boot's start time, from /proc/stat btime. Every process of an
// earlier boot ended before it.
export function bootTime() {
  const line = readFileSync("/proc/stat", "utf8").split("\n").find((l) => l.startsWith("btime "));
  return new Date(Number(line.slice(6)) * 1000).toISOString();
}

// A boot proof for a claim recorded under an earlier boot of this host. Its
// evidence is the boot change; it goes through the same verifier.
export function bootProof({ claim, conversation, execution, cohortRef, stop, now = () => new Date() }) {
  const terminatedAt = bootTime();
  const members = claim.engine?.pid && claim.engine?.start ? [{ pid: claim.engine.pid, boot: claim.host.bootId, startTicks: Number(claim.engine.start), terminatedAt }] : [];
  return sealProof(record("cohortProof", {
    id: newId("boot-proof"), authority: AUTHORITY, conversation, execution, cohortRef,
    membershipEpoch: claim.invocationId ?? `boot-${claim.host.bootId}`, membershipComplete: true, members,
    observedAt: now().toISOString(), verificationDigest: "", stop,
  }));
}