/** /api/health, /api/ready, /api/metrics — no cache, no envelope. */
import type { FastifyInstance } from "fastify";
import { performance, type EventLoopUtilization } from "node:perf_hooks";
import { pg } from "../lib/sql.js";
import { metrics } from "../metrics.js";
import { cacheStats } from "../cache.js";
import { redisPing } from "../redis.js";

export const API_VERSION = "0.1.0";

export async function systemRoutes(app: FastifyInstance): Promise<void> {
  app.get("/api/health", { schema: { summary: "Liveness (fast, no I/O)", tags: ["system"] } }, async (_req, reply) => {
    reply.header("cache-control", "no-store");
    return { ok: true, service: "dci-api", version: API_VERSION, uptimeSec: Math.round(process.uptime()), now: new Date().toISOString() };
  });

  app.get("/api/ready", { schema: { summary: "Readiness: Postgres ping (Redis reported, not required)", tags: ["system"] } }, async (_req, reply) => {
    reply.header("cache-control", "no-store");
    const started = Date.now();
    let db = false;
    let dbError: string | null = null;
    try {
      const sql = pg();
      await Promise.race([sql`select 1`, new Promise((_, rej) => setTimeout(() => rej(new Error("db timeout")), 3_000))]);
      db = true;
    } catch (e) {
      dbError = (e as Error).message;
    }
    const redis = await redisPing();
    const body = { ok: db, db, dbError, redis, dbLatencyMs: Date.now() - started, now: new Date().toISOString() };
    return reply.code(db ? 200 : 503).send(body);
  });

  app.get("/api/metrics", { schema: { summary: "Prometheus metrics", tags: ["system"] } }, async (_req, reply) => {
    const cs = cacheStats();
    const poolMax = Number(process.env.PG_POOL_MAX ?? 16);
    reply.header("cache-control", "no-store");
    reply.type("text/plain; version=0.0.4; charset=utf-8");
    return metrics.render({ dci_api_cache_memory_entries: cs.entries, dci_api_cache_memory_max: cs.max, dci_api_db_pool_max: poolMax, dci_api_process_rss_bytes: process.memoryUsage().rss, dci_api_event_loop_utilization: Math.round(performanceUtilization() * 1000) / 1000 });
  });
}

let lastElu: EventLoopUtilization | null = null;
function performanceUtilization(): number {
  const cur = lastElu ? performance.eventLoopUtilization(lastElu) : performance.eventLoopUtilization();
  lastElu = performance.eventLoopUtilization();
  return cur.utilization;
}