/**
 * Process supervision for long-running CLI commands (`index` / `init --index`).
 *
 * Indexing a large repo can run for a while on the main thread, and #999
 * surfaced two ways that goes wrong when nothing is watching it:
 *
 *   1. **Orphaned worker.** `index` runs in a child re-exec'd with
 *      `--liftoff-only` (the WASM-flag relaunch). Its parent blocks in
 *      `spawnSync`, so when the parent shim is killed it cannot forward the
 *      signal — the child keeps running, now orphaned, pinning a core. The PPID
 *      watchdog (#277) notices the parent/host went away and exits the child.
 *   2. **Wedged indexer.** The `#850` main-thread liveness watchdog — which
 *      SIGKILLs a process whose event loop stops turning — was wired only into
 *      the MCP `serve` path, so a wedged `index`/`init` was never auto-killed.
 *
 * Both reuse the exact mechanisms `serve` already uses; this just makes them
 * available to a one-shot command. Best-effort and self-disabling: a missing
 * watchdog never blocks the command from running. Both honour the same env
 * switches as `serve` (`CODEGRAPH_NO_WATCHDOG`, `CODEGRAPH_PPID_POLL_MS=0`).
 *
 * Unlike the daemon — whose main thread only does fast, bounded work — the
 * `index`/`init` path runs reference resolution and dynamic-edge synthesis
 * SYNCHRONOUSLY on this thread, and on a large repo that is legitimately many
 * seconds of work. So those spans yield cooperatively to the event loop
 * (`src/resolution/cooperative-yield.ts`) to keep the heartbeat alive; without
 * that the watchdog would SIGKILL a valid, in-progress index (#1091). The
 * distinction it must preserve — kill a TRUE wedge, spare slow-but-progressing
 * work — is exactly what cooperative yielding buys: a genuinely stuck span never
 * reaches its next yield, so it still trips the timeout.
 */
import { installMainThreadWatchdog, WatchdogOptions } from '../mcp/liveness-watchdog';
import { supervisionLostReason, parsePpidPollMs, parseHostPpid } from '../mcp/ppid-watchdog';
import { isProcessAlive } from '../mcp/daemon-registry';
import { EARLY_PPID } from '../mcp/early-ppid';
import { HOST_PPID_ENV } from '../extraction/wasm-runtime-flags';

export interface CommandSupervision {
  /** Tear down both watchdogs. Idempotent; call when the command finishes. */
  stop(): void;
}

/**
 * Install the liveness + PPID watchdogs for the duration of a CLI command.
 * `label` is used in the shutdown notice (e.g. `"index"`). Returns a handle
 * whose `stop()` must be called when the command completes so neither watchdog
 * outlives it.
 *
 * Pass `watchdog.progressPaths` (the project's SQLite DB + `-wal`) so the
 * liveness watchdog can tell a slow-but-progressing store on degraded storage
 * (files advancing) from a true wedge (they aren't) — one long synchronous
 * SQLite statement on a 150-IOPS disk otherwise gets a healthy index
 * SIGKILLed (#1231).
 */
export function installCommandSupervision(label: string, watchdog: WatchdogOptions = {}): CommandSupervision {
  // Liveness watchdog: a separate process that SIGKILLs us if our event loop
  // stops turning for too long (a wedged synchronous loop). Self-disables on
  // CODEGRAPH_NO_WATCHDOG.
  const liveness = installMainThreadWatchdog(watchdog);

  // PPID watchdog: detect that the parent (or the host threaded past the
  // relaunch shim) died and we've been orphaned, then exit instead of leaking.
  const stopParentWatch = watchParent((reason) => {
    try {
      process.stderr.write(`[CodeGraph ${label}] Parent process exited (${reason}); aborting.\n`);
    } catch { /* stderr gone with the parent — exit anyway */ }
    process.exit(1);
  });

  let stopped = false;
  return {
    stop(): void {
      if (stopped) return;
      stopped = true;
      stopParentWatch();
      liveness?.stop();
    },
  };
}

/**
 * Call `onLost` once, when the parent — or the host threaded past the
 * relaunch shim — goes away. The shim blocks in `spawnSync` and cannot forward
 * a signal, so this is how a re-exec'd child learns it was orphaned. Returns a
 * stop function. `CODEGRAPH_PPID_POLL_MS=0` disables it.
 */
export function watchParent(onLost: (reason: string) => void): () => void {
  // Baseline from the CLI entry's earliest-possible capture — reading
  // process.ppid here would miss a launcher killed during startup (#1185).
  const originalPpid = EARLY_PPID;
  const hostPpid = parseHostPpid(process.env[HOST_PPID_ENV]);
  const pollMs = parsePpidPollMs(process.env.CODEGRAPH_PPID_POLL_MS);
  if (pollMs <= 0) return () => {};
  const timer = setInterval(() => {
    const reason = supervisionLostReason({
      originalPpid,
      currentPpid: process.ppid,
      hostPpid,
      isAlive: isProcessAlive,
    });
    if (reason) {
      clearInterval(timer);
      onLost(reason);
    }
  }, pollMs);
  // Never let the watchdog itself keep the process alive past its real work.
  timer.unref();
  return () => clearInterval(timer);
}