import { Gauge } from './client'

const observers = new Map()

export default function <A extends Function> (fn: A, name: string, help: string = ''): A {
  if (!observers.has(name)) {
    observers.set(name, new Gauge({ name, help }))
  }

  const gauge = observers.get(name)

  return new Proxy(fn, {
    apply (target, context, args) {
      const end = gauge.startTimer()
      const result = Reflect.apply(target, context, args)

      if (result instanceof Promise) {
        result.then(() => end())
      } else {
        end()
      }

      return result
    }
  })
}