/**
 * @personal-blog/server — EPPP public server application.
 *
 * [E00-S02-T03] minimal serving process: a small HTTP server built on Node's
 * `node:http` (no runtime dependencies yet) that answers the application
 * health endpoint. `GET /health` reports a healthy application — HTTP 200 with
 * `{"status":"ok"}` — so the Compose stack's `app` service stays up and the
 * health endpoint succeeds once the stack is running.
 *
 * The Fastify 5 application shell (and the real HTTP API) lands in a later
 * story; this bootstrap keeps the application health-checkable until then.
 */

import { createServer, type IncomingMessage, type ServerResponse } from 'node:http';

/** Port the server listens on; `PORT` overrides the container default (3000). */
const PORT = resolvePort(process.env.PORT);

/** Health payload — reports a healthy application. */
const HEALTH_PAYLOAD = JSON.stringify({ status: 'ok' });

/** Payload for any route that is not the health endpoint. */
const NOT_FOUND_PAYLOAD = JSON.stringify({ error: 'not found' });

/**
 * Resolves the listen port from `PORT` (default 3000, matching the Dockerfile
 * `EXPOSE 3000` and the compose `:3000` container port). A non-numeric or
 * out-of-range override falls back to the default so a bad `PORT` value cannot
 * crash the process at startup.
 */
function resolvePort(raw: string | undefined): number {
  const port = Number(raw ?? 3000);
  return Number.isInteger(port) && port > 0 && port <= 65535 ? port : 3000;
}

/** Writes a JSON response with an explicit content-length. */
function sendJson(res: ServerResponse, statusCode: number, body: string): void {
  res.writeHead(statusCode, {
    'Content-Type': 'application/json; charset=utf-8',
    'Content-Length': Buffer.byteLength(body),
  });
  res.end(body);
}

/**
 * Routes one request. The application only serves the health endpoint at this
 * stage; anything else is a 404 so misconfiguration is loud.
 */
function handleRequest(req: IncomingMessage, res: ServerResponse): void {
  if (req.method === 'GET' && (req.url ?? '/') === '/health') {
    sendJson(res, 200, HEALTH_PAYLOAD);
    return;
  }
  sendJson(res, 404, NOT_FOUND_PAYLOAD);
}

const server = createServer(handleRequest);

server.listen(PORT, () => {
  console.log(`@personal-blog/server listening on http://0.0.0.0:${PORT} (health: GET /health)`);
});

// `docker stop` (Compose down) and Ctrl-C send SIGTERM/SIGINT — close the
// server and exit cleanly instead of being killed mid-request.
for (const signal of ['SIGTERM', 'SIGINT'] as const) {
  process.on(signal, () => {
    server.close(() => process.exit(0));
  });
}