import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
import { httpRequestDurationHistogram, httpRequestsCounter } from './metrics.js';

/**
 * Register HTTP request instrumentation for Prometheus metrics
 */
export async function registerInstrumentation(app: FastifyInstance): Promise<void> {
  app.addHook('onRequest', async (request: FastifyRequest, _reply: FastifyReply) => {
    (request as any).startTime = performance.now();
  });

  app.addHook('onResponse', async (request: FastifyRequest, reply: FastifyReply) => {
    const startTime = (request as any).startTime;
    if (startTime === undefined) return;

    const duration = (performance.now() - startTime) / 1000; // Convert to seconds
    const method = request.method;
    const route = request.routeOptions?.url || request.url.split('?')[0] || 'unknown';
    const statusCode = reply.statusCode.toString();

    // Record metrics
    httpRequestDurationHistogram.observe({ method, route, status_code: statusCode }, duration);
    httpRequestsCounter.inc({ method, route, status_code: statusCode });
  });
}