gui.widgets.ScrollArea = {
  new: func(parent, style, cfg)
  {
    var cfg = Config.new(cfg);
    var m = gui.Widget.new(gui.widgets.ScrollArea);
    m._focus_policy = m.NoFocus;
    m._scroll_pos = [0,0];
    m._max_scroll = [0, 0];
    m._content_size = [0, 0];
    m._layout = nil;

    if( style != nil )
      m._setView( style.createWidget(parent, "scroll-area", cfg) );

    m.setMinimumSize([32, 32]);

    return m;
  },
  setLayout: func(l)
  {
    me._layout = l;
    l.setParent(me);
    return me.update();
  },
  getContent: func()
  {
    return me._view.content;
  },
  # Set the background color for the content area.
  #
  # @param color  Vector of 3 or 4 values in [0, 1]
  setColorBackground: func
  {
    if( size(arg) == 1 )
      var arg = arg[0];
    me._view.setColorBackground(arg);
  },
  # Reset the size of the content area, e.g. on window resize.
  #
  # @param sz  Vector of [x,y] values.
  setSize: func
  {
    if( size(arg) == 1 )
      var arg = arg[0];
    var (x,y) = arg;
    me._size = [x,y];
    me.update();

    if( me._layout != nil )
      me._layout.setGeometry(me._layout.geometry());
  },
  # Move the scrollbars to the coordinates x,y (or as far as possible) and
  # update.
  #
  # @param x The x coordinate (positive is right)
  # @param y The y coordinate (positive is down)
  moveTo: func(x, y)
  {
    var bb = me._updateBB();

    me._scroll_pos[0] = math.max(0, math.min(x, me._max_scroll[0]));
    me._scroll_pos[1] = math.max(0, math.min(y, me._max_scroll[1]));

    me.update(bb);
  },
  # Move the scrollable area to the top-most position and update.
  moveToTop: func()
  {
    me._scroll_pos[1] = 0;

    me.update();
  },
  # Move the scrollable area to the bottom-most position and update.
  moveToBottom: func()
  {
    var bb = me._updateBB();

    me._scroll_pos[1] = me._max_scroll[1];

    me.update(bb);
  },
  # Move the scrollable area to the left-most position and update.
  moveToLeft: func()
  {
    me._scroll_pos[0] = 0;

    me.update();
  },
  # Move the scrollable area to the right-most position and update.
  moveToRight: func()
  {
    var bb = me._updateBB();

    me._scroll_pos[0] = me._max_scroll[0];

    me.update(bb);
  },
  # Get position of scrollable content
  getContentPosition: func()
  {
    var pos = [0, 0];

    if( me._max_scroll[0] > 1 )
      pos[0] = (me._scroll_pos[0] / me._max_scroll[0])
             * (me._content_size[0] - me._size[0]);
    if( me._max_scroll[1] > 1 )
      pos[1] = (me._scroll_pos[1] / me._max_scroll[1])
             * (me._content_size[1] - me._size[1]);

    return pos;
  },
  # Move content to the given position
  moveContentTo: func(x, y)
  {
    var scroll_x = x / (me._content_size[0] - me._size[0]) * me._max_scroll[0];
    var scroll_y = y / (me._content_size[1] - me._size[1]) * me._max_scroll[1];

    return me.moveTo(scroll_x, scroll_y);
  },
  # Update scroll bar and content area.
  #
  # Needs to be called when the size of the content changes.
  update: func(bb=nil)
  {
    if (bb == nil) bb = me._updateBB();
    if (bb == nil) return me;

    var pos = me.getContentPosition();
    var offset = [ me._content_offset[0] - pos[0],
                   me._content_offset[1] - pos[1] ];
    me.getContent().setTranslation(offset);

    me._view.update(me);
    me.getContent().update();

    return me;
  },
# protected:
  _setView: func(view)
  {
    view.vert.addEventListener("mousedown", func(e) me._dragStart(e));
    view.horiz.addEventListener("mousedown", func(e) me._dragStart(e));
    view._root.addEventListener("mousedown", func(e)
    {
      var pos = me.getContentPosition();
      me._drag_offsetX = pos[0] + e.clientX;
      me._drag_offsetY = pos[1] + e.clientY;
    });

    view.vert.addEventListener
    (
      "drag",
      func(e)
      {
        if( !me._enabled )
          return;

        me.moveTo(me._scroll_pos[0], me._drag_offsetY + e.clientY);
        e.stopPropagation();
      }
    );
    view.horiz.addEventListener
    (
      "drag",
      func(e)
      {
        if( !me._enabled )
          return;

        me.moveTo(me._drag_offsetX + e.clientX, me._scroll_pos[1]);
        e.stopPropagation();
      }
    );

    view._root.addEventListener
    (
      "drag",
      func(e)
      {
        if( !me._enabled )
          return;

        me.moveContentTo( me._drag_offsetX - e.clientX,
                          me._drag_offsetY - e.clientY );
        e.stopPropagation();
      }
    );
    view._root.addEventListener
    (
      "wheel",
      func(e)
      {
        if( !me._enabled )
          return;

        me.moveTo(me._scroll_pos[0], me._scroll_pos[1] - e.deltaY);
        e.stopPropagation();
      }
    );

    call(gui.Widget._setView, [view], me);
  },
  _dragStart: func(e)
  {
    me._drag_offsetX = me._scroll_pos[0] - e.clientX;
    me._drag_offsetY = me._scroll_pos[1] - e.clientY;
    e.stopPropagation();
  },
  _updateBB: func()
  {
    # TODO only update on content resize
    if( me._layout == nil )
    {
      var bb = me.getContent().getTightBoundingBox();

      if( bb[2] < bb[0] or bb[3] < bb[1] )
        return nil;
      var w = bb[2] - bb[0];
      var h = bb[3] - bb[1];

      var cur_offset = me.getContent().getTranslation();
      me._content_offset = [cur_offset[0] - bb[0], cur_offset[1] - bb[1]];
    }
    else
    {
      var min_size = me._layout.minimumSize();
      var max_size = me._layout.maximumSize();
      var size_hint = me._layout.sizeHint();
      var w = math.min(max_size[0], math.max(size_hint[0], me._size[0]));
      var h = math.max(
              math.min(max_size[1], math.max(size_hint[1], me._size[1])),
              me._layout.heightForWidth(w)
            );

      me._layout.setGeometry([0, 0, w, h]);

      # Layout always has the origin at (0, 0)
      me._content_offset = [0, 0];
    }

    if( w > me._size[0] )
    {
      var scroller_size = math.max(12, me._size[0] * (me._size[0] / w));
      me._max_scroll[0] = me._size[0] - scroller_size;
    }
    else
      me._max_scroll[0] = 0;

    if( h > me._size[1] )
    {
      var scroller_size = math.max(12, me._size[1] * (me._size[1] / h));
      me._max_scroll[1] = me._size[1] - scroller_size;
    }
    else
      me._max_scroll[1] = 0;

    me._content_size[0] = w;
    me._content_size[1] = h;
  }
};