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

function createHealthRouter(connectors = []) {
  const router = express.Router();

  router.get('/', async (req, res) => {
    const connectorStatuses = connectors.map((connector) => connector.health());
    const pending = await queue.pendingCount();
    const retrying = await queue.retryingCount();
    const deadLetters = await queue.deadLetterCount();
    res.json({
      status: 'ok',
      connectors: connectorStatuses,
      metrics: {
        pending,
        retrying,
        deadLetters
      }
    });
  });

  router.get('/ready', async (req, res) => {
    try {
      await queue.ping();
      res.json({ status: 'ready' });
    } catch (err) {
      res.status(503).json({ status: 'unready', reason: err.message });
    }
  });

  return router;
}

const instrumentRouter = express.Router();

instrumentRouter.get('/', async (req, res) => {
  res.json(instrumentConfig.list());
});

instrumentRouter.get('/:id', async (req, res) => {
  const entry = instrumentConfig.get(req.params.id);
  if (!entry) {
    return res.status(404).json({ error: 'not found' });
  }
  res.json(entry);
});

const metricsRouter = express.Router();

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');
}

metricsRouter.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');
  }
});

function createHttpServer(connectors) {
  const app = express();
  app.use('/health', createHealthRouter(connectors));
  app.use('/instruments', instrumentRouter);
  app.use('/metrics', metricsRouter);
  return app;
}

module.exports = { createHttpServer };