import { monitorEventLoopDelay } from "node:perf_hooks";
import { logger, serializeError } from "../logger.js";

export const installProcessObservability = (options: {
  workers: () => Promise<number>;
}): void => {
  process.on("uncaughtException", (err) => {
    logger.fatal({ err: serializeError(err) }, "uncaught exception");
    setTimeout(() => process.exit(1), 1_000);
  });
  process.on("unhandledRejection", (reason) => {
    logger.fatal({ err: serializeError(reason) }, "unhandled rejection");
  });
  const eventLoopDelay = monitorEventLoopDelay({ resolution: 20 });
  eventLoopDelay.enable();
  const heartbeat = async (): Promise<void> => {
    const memory = process.memoryUsage();
    logger.info(
      {
        operation: "heartbeat",
        uptimeSeconds: Math.round(process.uptime()),
        workers: await options.workers().catch(() => -1),
        rssBytes: memory.rss,
        heapUsedBytes: memory.heapUsed,
        eventLoopLagMs: eventLoopDelay.mean / 1e6,
      },
      "pinboard heartbeat",
    );
    eventLoopDelay.reset();
  };
  setInterval(() => {
    heartbeat().catch((error) => {
      logger.error(
        { source: "heartbeat", err: serializeError(error) },
        "background loop error",
      );
    });
  }, 60_000).unref();
};