add smooth scrolling (lines 11-18) & allow nested lists of spies

scrollspy.coffee

angular.module('directives.scrollSpy', [])

.directive('spy', ($location) ->
  restrict: 'A'
  require: '^scrollSpy'
  link: (scope, elem, attrs, scrollSpy) ->
    attrs.spyClass ?= 'active'

    elem.click (e) ->
      e.stopPropagation()
      if attrs.spy
        target = $('#' + attrs.spy)
        speed = 750
        $('html, body').stop().animate
          scrollTop: target.offset().top + 1
          speed
          easeInOutCubuc = (x, t, b, c, d) ->
            c * ((t = t / d - 1) * t * t + 1) + b
      else
        $('html, body').stop().animate scrollTop: 0, speed

    scrollSpy.addSpy
      id: attrs.spy
      in: ->
        elem.addClass attrs.spyClass
        elem.parents('li').addClass attrs.spyClass
      out: -> elem.removeClass attrs.spyClass
)

.directive('scrollSpy', ($window, $timeout) ->
  restrict: 'A'
  controller: ($scope) ->
    $scope.spies = []
    @addSpy = (spyObj) ->
      $scope.spies.push spyObj
    return
  scope: true
  link: (scope, elem, attrs) ->
    spyElems = []
    topBuffer = if attrs.topBuffer then attrs.topBuffer else 0

    scope.$watchCollection 'spies', (spies) ->
      for spy in spies
        unless spyElems[spy.id]?
          spyElems[spy.id] = elem.find('#' + spy.id)

    $($window).scroll ->
      highlightSpy = null
      for spy in scope.spies
        spy.out()

        if !spyElems[spy.id]? or spyElems.length is 0
          spyElems[spy.id] = elem.find('#' + spy.id)

        if spyElems[spy.id]? and spyElems[spy.id].length isnt 0
          # TODO: fix for IE9+ ?
          # https://gist.github.com/alxhill/6886760#comment-952714
          if (pos = spyElems[spy.id].offset().top) - $window.pageYOffset <= topBuffer
          # if (pos = spyElems[spy.id].offset().top) - $window.scrollY <= topBuffer
            spy.pos = pos
            highlightSpy ?=spy
            if highlightSpy.pos < spy.pos
              highlightSpy = spy

      highlightSpy?.in()
)