Make "to top" link visible when scrolling through the log

These are the changes by @dmathieu (reverted at d7bef2b) slightly
changed to allow us to use them also on Travis Pro.

The change is to still use onScroll calculations in order to position
elements instead of using "position: fixed". The latter method is harder
to use when element needs to be positioned relatively to other element -
on Pro we would have to still calculate the position because of the
right sidebar.

assets/scripts/app/app.coffee

@@ -35,7 +35,8 @@ unless window.TravisApplication
 
       @slider = new Travis.Slider()
       @pusher = new Travis.Pusher(Travis.config.pusher_key) if Travis.config.pusher_key
-      @tailing = new Travis.Tailing()
+      @tailing = new Travis.Tailing($(window), '#tail', '#log')
+      @toTop   = new Travis.ToTop($(window), '.to-top', '#log-container')
 
       @set('auth', Travis.Auth.create(app: this, endpoint: Travis.config.api_endpoint))
 

assets/scripts/app/tailing.coffee

@@ -1,12 +1,51 @@
-@Travis.Tailing = ->
-  @position = $(window).scrollTop()
-  $(window).scroll( $.throttle( 200, @onScroll.bind(this) ) )
+class Travis.ToTop
+  # NOTE: I could have probably extract fixed positioning from
+  #       Tailing, but then I would need to parametrize positionElement
+  #       function to make it flexible to handle both cases. In that
+  #       situation I prefer a bit less DRY code over simplicity of
+  #       the calculations.
+  constructor: (@window, @element_selector, @container_selector) ->
+    @position = @window.scrollTop()
+    @window.scroll( $.throttle( 200, @onScroll.bind(this) ) )
     this
 
-$.extend Travis.Tailing.prototype,
+  element: ->
+    $(@element_selector)
+  container: ->
+    $(@container_selector)
+
+  onScroll: ->
+    @positionElement()
+
+  positionElement: ->
+    element = @element()
+    container = @container()
+    return if element.length is 0
+    containerHeight = container.height()
+    windowHeight = @window.height()
+    offset = container.offset().top + containerHeight - (@window.scrollTop() + windowHeight)
+    max = containerHeight - windowHeight
+    offset = max if offset > max
+    console.log(offset, max)
+    if offset > 0
+      element.css(bottom: offset)
+    else
+      element.css(bottom: 2)
+
+class @Travis.Tailing
   options:
     timeout: 200
 
+  tail: ->
+    $(@tail_selector)
+  log: ->
+    $(@log_selector)
+
+  constructor: (@window, @tail_selector, @log_selector) ->
+    @position = @window.scrollTop()
+    @window.scroll( $.throttle( 200, @onScroll.bind(this) ) )
+    this
+
   run: ->
     @autoScroll()
     @positionButton()
@@ -16,37 +55,43 @@ $.extend Travis.Tailing.prototype,
     if @active() then @stop() else @start()
 
   active: ->
-    $('#tail').hasClass('active')
+    @tail().hasClass('active')
 
   start: ->
-    $('#tail').addClass('active')
+    @tail().addClass('active')
     @run()
 
   stop: ->
-    $('#tail').removeClass('active')
+    @tail().removeClass('active')
 
   autoScroll: ->
-    return unless @active()
-    win = $(window)
-    log = $('#log')
-    logBottom = log.offset().top + log.outerHeight() + 40
-    winBottom = win.scrollTop() + win.height()
-    win.scrollTop(logBottom - win.height()) if logBottom - winBottom > 0
+    return false unless @active()
+    logBottom = @log().offset().top + @log().outerHeight() + 40
+    winBottom = @window.scrollTop() + @window.height()
+
+    if logBottom - winBottom > 0
+      @window.scrollTop(logBottom - @window.height())
+      true
+    else
+      false
 
   onScroll: ->
     @positionButton()
-    position = $(window).scrollTop()
+    position = @window.scrollTop()
     @stop() if position < @position
     @position = position
 
   positionButton: ->
-    tail = $('#tail')
-    return if tail.length is 0
-    offset = $(window).scrollTop() - $('#log').offset().top
-    max = $('#log').height() - $('#tail').height() + 5
-    offset = max if offset > max
-    if offset > 0
-      tail.css(top: offset - 2)
-    else
-      tail.css(top: 0)
+    return if @tail().length is 0
+    offset = @window.scrollTop() - @log().offset().top
+    max = @log().height() - @tail().height() + 5
 
+    if offset > 0 && offset <= max
+      @tail().removeClass('bottom')
+      @tail().addClass('scrolling')
+    else
+      if offset > max
+        @tail().addClass('bottom')
+      else
+        @tail().removeClass('bottom')
+      @tail().removeClass('scrolling')

assets/scripts/app/templates/jobs/pre.hbs

@@ -1,7 +1,14 @@
 <div id="log-container">
   <a href="#" id="tail" {{action "toggleTailing" target="view"}}>
     <span class="status"></span>
-    <label>Follow logs</label>
+
+    <label>
+      {{#if view.job.isFinished}}
+        Scroll to end of logs
+      {{else}}
+        Follow logs
+      {{/if}}
+    </label>
   </a>
   <pre id="log" class="ansi"></pre>
 

assets/scripts/spec/unit/tailing_spec.coffee

@@ -0,0 +1,89 @@
+fakeWindow =
+  scroll: sinon.spy()
+  scrollTop: sinon.stub().returns(0)
+  height: sinon.stub().returns(40)
+element = jQuery('<div id="specTail"></div>')
+log     = jQuery('<div id="specLog"></div>')
+tail = new Travis.Tailing(fakeWindow, '#specTail', '#specLog')
+tail.tail = -> element
+tail.log  = -> log
+
+module "Travis.Tailing",
+  setup: ->
+    jQuery('body').append(element)
+    jQuery('body').append(log)
+
+  teardown: ->
+    element.remove()
+    log.remove()
+    tail.stop()
+
+test "toggle", ->
+  equal(element.hasClass('active'), false)
+  tail.toggle()
+  equal(element.hasClass('active'), true)
+  tail.toggle()
+  stop()
+
+  Ember.run.later ->
+    start()
+    equal(element.hasClass('active'), false)
+  , 300
+
+test "active", ->
+  equal(tail.active(), false)
+  element.addClass('active')
+  equal(tail.active(), true)
+
+test "autoscroll when inactive", ->
+  tail.scrollTo = sinon.spy()
+
+  equal(tail.active(), false)
+  equal(tail.autoScroll(), false)
+  equal(tail.scrollTo.called, false)
+
+test "autoscroll", ->
+  element.addClass('active')
+  log.offset = -> {top: 1}
+  log.outerHeight = -> 1
+
+  equal(tail.active(), true)
+  equal(tail.autoScroll(), true)
+  equal(fakeWindow.scrollTop.calledWith(2), true)
+
+test "autoscroll when we're at the bottom", ->
+  element.addClass('active')
+  log.offset = -> {top: 0}
+  log.outerHeight = -> 0
+
+  equal(tail.active(), true)
+  equal(tail.autoScroll(), false)
+  equal(fakeWindow.scrollTop.calledWith(0), false)
+
+test 'should stop scrolling if the position changed', ->
+  element.addClass('active')
+  tail.position = 100
+  tail.onScroll()
+  equal(element.hasClass('active'), false)
+
+test 'positionButton adds the scrolling class', ->
+  log.offset = -> {top: -1}
+
+  tail.positionButton()
+  equal(element.hasClass('scrolling'), true)
+  equal(element.hasClass('bottom'), false)
+
+test 'positionButton removes the scrolling class', ->
+  log.offset = -> {top: 1}
+  tail.positionButton()
+  equal(element.hasClass('scrolling'), false)
+  equal(element.hasClass('bottom'), false)
+
+test 'positionButton sets the button as bottom', ->
+  log.offset  = -> {top: -100}
+  log.height  = -> 50
+  tail.height = -> 1
+
+  tail.positionButton()
+  equal(element.hasClass('scrolling'), false)
+  equal(element.hasClass('bottom'), true)

assets/styles/main/log.sass

@@ -88,7 +88,8 @@ pre#log
 #log-container
   position: relative
 
-#log-container #tail
+#log-container
+  #tail
     z-index: 99
     position: absolute
     display: block
@@ -118,6 +119,14 @@ pre#log
       label
         display: inline
 
+    &.scrolling
+      position: fixed
+      right: 32px
+
+    &.bottom
+      bottom: 45px
+      top: inherit
+
     .status
       display: inline-block
       margin-right: 1px
@@ -129,3 +138,17 @@ pre#log
 
     &.active .status
       background-color: #6b0
+
+  .to-top
+    z-index: 99
+    position: absolute
+    display: block
+    bottom: 2px
+    right: 2px
+
+    width: 50px
+    margin-right: 2px
+    padding-right: 16px
+    text-align: right
+    color: #999
+    background: inline-image('ui/to-top.png') no-repeat right 6px

assets/styles/main/sponsors.sass

@@ -3,12 +3,3 @@
     // float: left
     margin-top: 0
     color: #999
-  .to-top
-    display: inline-block
-    width: 50px
-    float: right
-    margin-right: 2px
-    padding-right: 16px
-    text-align: right
-    color: #999
-    background: inline-image('ui/to-top.png') no-repeat right 6px