// The audit handler — appends one line per event to an append-only audit log. It is the whole of
// the module's code: an audit logger is not a privileged component, only a module that listens to
// everything and writes it down (novox/hq ADR 0041).

import { appendFile, mkdir } from "node:fs/promises";
import { dirname } from "node:path";
import type { Event } from "@novox/mesh-sdk/events";

/** Where the trail is written. A directory the host applies; one file per node. */
export function auditLogPath(env: NodeJS.ProcessEnv = process.env): string {
  return env.AUDIT_LOG ?? "/var/lib/audit-logger/audit.log";
}

/** Append an event to the trail as one JSON line, keeping the metadata an audit needs first. The id
 *  is the event's own x-event-id (ADR 0042) — the handle a reader dedups the at-least-once trail on. */
export async function record(event: Event, path: string): Promise<void> {
  const line =
    JSON.stringify({
      id: event.id,
      type: event.type,
      source: event.source,
      node: event.node,
      at: event.at,
      ...(event.causationId ? { causationId: event.causationId } : {}),
      ...(event.schema ? { schema: event.schema } : {}),
      body: event.body,
    }) + "\n";
  await mkdir(dirname(path), { recursive: true }).catch(() => {});
  await appendFile(path, line, { mode: 0o600 });
}