import { Router, type Request, type Response } from 'express';
import { Gauge, register } from 'prom-client';
import type { StorageServiceInterface } from '../services/storageInterface.js';
import { logger } from '../lib/logger.js';

export function createMetricsRouter(storage: StorageServiceInterface): Router {
  const router = Router();

  const gauge = new Gauge({
    name: 'relay_storage_entries',
    help: 'Number of stored entries by kind',
    labelNames: ['kind'],
  });

  /**
   * GET /metrics - Prometheus metrics.
   */
  router.get('/', (_req: Request, res: Response): void => {
    void (async (): Promise<void> => {
      try {
        const msgCount = storage.getMessages(0, Number.MAX_SAFE_INTEGER).length;
        gauge.set({ kind: 'messages' }, msgCount);
        gauge.set({ kind: 'signatures' }, storage.getSignatureCount());
        gauge.set({ kind: 'keys' }, storage.getKeyCount());
        gauge.set({ kind: 'seen_hashes' }, storage.getSeenHashCount());

        res.set('Content-Type', register.contentType);
        res.send(await register.metrics());
      } catch (err) {
        logger.error({ err }, 'Error generating metrics');
        res.status(500).json({ error: 'Internal server error' });
      }
    })();
  });

  return router;
}