module.exports = debounce

function debounce (fn, delay, at_start, guarantee) {
  var timeout
  var args
  var self

  return function debounced () {
    self = this
    args = Array.prototype.slice.call(arguments)

    if (timeout && (at_start || guarantee)) {
      return
    } else if (!at_start) {
      clear()

      timeout = setTimeout(run, delay)
      return timeout
    }

    timeout = setTimeout(clear, delay)
    fn.apply(self, args)

    function run () {
      clear()
      fn.apply(self, args)
    }

    function clear () {
      clearTimeout(timeout)
      timeout = null
    }
  }
}