feat(position): implement directional positioning

[wesleycho]

• When positioning based off position or offset, allow specification of direction

I will work on tests for this, but I am opening this up for review so that this code can be cleaned up some (I'm not a fan of all of these if conditionals here).

This will assist with #3782 with a cleaner implementation. Implementing this part is as simple as changing template/datepicker/popup.html to

<ul class="dropdown-menu"
  ng-style="{
    display: (isOpen && 'block') || 'none',
    top: position.top,
    right: position.right,
    bottom: position.bottom,
    left: position.left
  }"
  ng-keydown="keydown($event)">

And the relevant lines in the datepickerPopup directive to

      scope.$watch('isOpen', function(value) {
        if (value) {
          scope.$broadcast('datepicker.focus');
          scope.position = $position.placement(element, attrs.datepickerPlacement, appendToBody);
          if (angular.isNumber(scope.position.bottom)) {
            if (appendToBody) scope.position.bottom -= element.prop('offsetHeight');
            scope.position.bottom += 'px';
            scope.position.top = 'initial';
          } else {
            scope.position.bottom = 'initial';
            if (!appendToBody) scope.position.top += element.prop('offsetHeight');
            scope.position.top += 'px';
          }

          if (angular.isNumber(scope.position.right)) {
            scope.position.left = 'initial';
            scope.position.right += 'px';
          } else {
            scope.position.left += 'px';
            scope.position.right = 'initial';
          }

          $document.bind('click', documentClickBind);
        } else {
          $document.unbind('click', documentClickBind);
        }
      });

Here is a Plunker with those changes implemented.

[wesleycho]

It might make sense to move the conditional adding and subtracting of top and bottom values in that code block example to the placement method.

It also might make sense to just move all of the CSS logic right into the method as well.

[chrisirhc]

I'm quite confused about this line and 92-94. What are these cases? Are they fallbacks?

[wesleycho]

92-94 is the default case if it is a string but invalid value.

96-98 is the default case if it has no value set.

[chrisirhc]

If it's the default case, perhaps it be handled via a isInvalid flag (or isDefaultPosition) or something, and a check below, since the code is identical, might make sense to put it together.

[wesleycho]

Makes sense - I am not happy with how I wrote this, there are too many if-else conditionals here.

[icfantv]

Closing in favor of #4762.