/**
 * Minimal HTTP server shared by the worker (`main.ts`) and the standalone scheduler (`scheduler.ts`):
 *   GET /healthz  → JSON from `health()`; 503 while `ready()` is false (shutting down / not started)
 *   GET /metrics  → Prometheus text from prom.ts after `beforeScrape()` refreshed the gauges
 * Never throws into the caller; errors become 500 JSON responses.
 */
import { createServer, type Server } from "node:http";
import { renderMetrics } from "./prom.js";

export interface HealthHttpOptions {
  port: number;
  role: string;
  health: () => Promise<Record<string, unknown>>;
  ready: () => boolean;
  /** refresh snapshot gauges (queue depth, budgets…) right before rendering */
  beforeScrape?: () => Promise<void>;
  log?: (msg: string) => void;
  /** extra JSON routes keyed by path prefix ("/trace" matches "/trace/<id>") */
  routes?: Record<string, (url: URL) => Promise<{ status: number; body: unknown }>>;
}

export function startHealthHttp(o: HealthHttpOptions): Server {
  const log = o.log ?? ((m: string) => console.error(`[${o.role}] ${m}`));
  const server = createServer(async (req, res) => {
    try {
      const url = new URL(req.url ?? "/", "http://localhost");
      if (url.pathname === "/healthz" || url.pathname === "/") {
        const body = await o.health();
        const ok = o.ready();
        res.writeHead(ok ? 200 : 503, { "content-type": "application/json", "cache-control": "no-store" });
        res.end(JSON.stringify({ ok, role: o.role, ...body }, null, 2));
        return;
      }
      if (url.pathname === "/metrics") {
        if (o.beforeScrape) await o.beforeScrape().catch((e: Error) => log(`metrics refresh failed: ${e.message}`));
        res.writeHead(200, { "content-type": "text/plain; version=0.0.4; charset=utf-8", "cache-control": "no-store" });
        res.end(renderMetrics());
        return;
      }
      for (const [prefix, handler] of Object.entries(o.routes ?? {})) {
        if (url.pathname === prefix || url.pathname.startsWith(`${prefix}/`)) {
          const r = await handler(url);
          res.writeHead(r.status, { "content-type": "application/json", "cache-control": "no-store" });
          res.end(JSON.stringify(r.body));
          return;
        }
      }
      res.writeHead(404, { "content-type": "application/json" });
      res.end(JSON.stringify({ error: "not found" }));
    } catch (e) {
      res.writeHead(500, { "content-type": "application/json" });
      res.end(JSON.stringify({ error: (e as Error).message }));
    }
  });
  server.on("error", (e) => log(`http error: ${e.message}`));
  server.listen(o.port, "0.0.0.0", () => log(`http :${o.port} (/healthz, /metrics)`));
  return server;
}