const client = require("prom-client");

function resolveRouteLabel(request) {
  const url = request?.routeOptions?.url;
  if (typeof url === "string" && url.trim()) {
    return url;
  }

  const routerPath = request?.routerPath;
  if (typeof routerPath === "string" && routerPath.trim()) {
    return routerPath;
  }

  const rawUrl = request?.raw?.url;
  if (typeof rawUrl === "string" && rawUrl.trim()) {
    return rawUrl.split("?")[0];
  }

  return "unknown";
}

function initMetrics(app) {
  const registry = new client.Registry();

  client.collectDefaultMetrics({
    register: registry,
  });

  const httpRequestsTotal = new client.Counter({
    name: "hyb_http_requests_total",
    help: "Total number of HTTP requests",
    labelNames: ["method", "route", "status_code"],
    registers: [registry],
  });

  const httpRequestDurationSeconds = new client.Histogram({
    name: "hyb_http_request_duration_seconds",
    help: "HTTP request duration in seconds",
    labelNames: ["method", "route", "status_code"],
    buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10],
    registers: [registry],
  });

  const jobRunsTotal = new client.Counter({
    name: "hyb_job_runs_total",
    help: "Total number of background job runs",
    labelNames: ["job", "driver", "outcome"],
    registers: [registry],
  });

  const jobProcessedTotal = new client.Counter({
    name: "hyb_job_processed_total",
    help: "Total number of processed items per job",
    labelNames: ["job", "driver", "kind"],
    registers: [registry],
  });

  const dbReady = new client.Gauge({
    name: "hyb_db_ready",
    help: "Database readiness probe result (1=ready, 0=not ready)",
    registers: [registry],
  });

  app.decorate("metrics", {
    registry,
    httpRequestsTotal,
    httpRequestDurationSeconds,
    jobRunsTotal,
    jobProcessedTotal,
    dbReady,
  });

  app.decorateRequest("metricsStart", null);

  app.addHook("onRequest", async (request) => {
    request.metricsStart = process.hrtime.bigint();
  });

  app.addHook("onResponse", async (request, reply) => {
    const start = request.metricsStart;
    if (typeof start !== "bigint") {
      return;
    }

    const end = process.hrtime.bigint();
    const durationSeconds = Number(end - start) / 1e9;

    const method = request.method;
    const route = resolveRouteLabel(request);
    const statusCode = String(reply.statusCode);

    httpRequestsTotal.inc({ method, route, status_code: statusCode });
    httpRequestDurationSeconds.observe(
      { method, route, status_code: statusCode },
      durationSeconds,
    );
  });

  return app.metrics;
}

module.exports = {
  initMetrics,
};