import prometheus, {
  collectDefaultMetrics,
  LabelValues,
  Histogram,
  Registry,
} from 'prom-client'
import express from 'express'
import { Server } from 'net'
import { Logger } from '..'

export interface Metrics {
  client: typeof prometheus
  registry: Registry
}

export const createMetrics = (): Metrics => {
  // Collect default metrics (event loop lag, memory, file descriptors etc.)
  collectDefaultMetrics()

  return { client: prometheus, registry: prometheus.register }
}

export interface MetricsServerOptions {
  logger: Logger
  registry: Registry
  port?: number
  route?: string
}

export const createMetricsServer = (options: MetricsServerOptions): Server => {
  const logger = options.logger.child({ component: 'MetricsServer' })

  const app = express()

  app.get(options.route || '/metrics', async (_, res) => {
    res.set('Content-Type', options.registry.contentType)
    res.status(200).send(await options.registry.metrics())
  })

  const port = options.port || 7300
  const server = app.listen(port, () => {
    logger.debug('Listening on port', { port })
  })

  return server
}

export async function timed<T>(
  metric: Histogram<string> | undefined,
  labels: LabelValues<string> | undefined,
  promise: T | Promise<T>,
): Promise<T> {
  const timer = metric?.startTimer(labels)
  try {
    return await promise
  } finally {
    if (timer) {
      timer(labels)
    }
  }
}