const express = require('express');
const queue = require('../queue/queue');

function formatMetric(name, value, type = 'gauge', help = '') {
  const lines = [];
  if (help) {
    lines.push(`# HELP ${name} ${help}`);
  }
  lines.push(`# TYPE ${name} ${type}`);
  lines.push(`${name} ${value}`);
  return lines.join('\n');
}

function createMetricsRouter() {
  const router = express.Router();

  router.get('/', async (req, res) => {
    try {
      const pending = await queue.pendingCount();
      const retrying = await queue.retryingCount();
      const deadLetters = await queue.deadLetterCount();
      const lastSuccess = await queue.getLastSuccessTimestamp();
      const avgLatency = await queue.getAverageLatency();
      const attempts = await queue.getDeliveryAttempts();
      const timestamp = lastSuccess ? new Date(lastSuccess).getTime() / 1000 : 0;
      const metrics = [
        formatMetric('workstation_pending_total', pending, 'gauge', 'Number of pending payloads'),
        formatMetric('workstation_retrying_total', retrying, 'gauge', 'Number of payloads currently retrying'),
        formatMetric('workstation_dead_letters_total', deadLetters, 'gauge', 'Total dead-lettered payloads'),
        formatMetric('workstation_delivery_attempts_total', attempts, 'counter', 'Total delivery attempts logged'),
        formatMetric('workstation_last_success_timestamp', timestamp, 'gauge', 'Epoch seconds of last successful delivery'),
        formatMetric('workstation_avg_latency_ms', Math.round(avgLatency), 'gauge', 'Average delivery latency in milliseconds')
      ];
      res.set('content-type', 'text/plain; version=0.0.4; charset=utf-8');
      res.send(metrics.join('\n'));
    } catch (error) {
      res.status(500).send('metrics unavailable');
    }
  });

  return router;
}

module.exports = { createMetricsRouter };