jquery.smoothsnap.coffee

#
# Usage:
#  ($ '#main').smoothsnap snap: 'h3'
#  or
#  ($ '#main').smoothsnap snap: $ 'h3'

(

  ($) ->

    class SmoothSnap

      contructor: (selector) ->
        selector = $ selector
        for i in [0...selector.length]
          @points.push selector[i].offsetTop

      points: []

      point: (point) ->
        return null if @points.length is 0
        return @points[0] if @points.length is 1
        dist = null
        dist_p = Math.abs point - @points[0]
        for i in [0...@points.length]
          dist = Math.abs point - @points[i]
          return @points[i - 1] if dist_p < dist
          dist_p = dist
        return @points[@points.length - 1]

      distance: (num) ->
        if num > 0 then return Math.exp num / 30
        if num < 0 then return -1 * Math.exp Math.abs(num) / 30
        return 0

    defaults =
      target: ($ 'body')
      snap: null

    state =
      mouse: null
      target: null
      mousePress: no

    $.fn.smoothsnap = (opts, callback) ->
      $.extend defaults, opts
      callback or= ->

      smoothsnap = new SmoothSnap opts.snap

      @css
        '-webkit-user-select': 'none'
        '-moz-user-select': 'none'

      @on 'mousedown', (event) ->
        state.mouse = event.screenY
        state.target = window.scrollY
        state.mousePress = on

      @on 'mouseup', (event) ->
        state.mouse = null
        state.mousePress = off

      @on 'mousemove', (event) ->
        if state.mousePress
          dy = event.screenY - state.mouse
          y = state.target + smoothsnap.distance dy
          window.scrollTo window.scrollX, smoothsnap.point y

      return this

) jQuery