/*
* jQuery dragscrollable Plugin
* version: 1.0 (25-Jun-2009)
* Copyright (c) 2009 Miquel Herrera
*
* Dual licensed under the MIT and GPL licenses:
*   http://www.opensource.org/licenses/mit-license.php
*   http://www.gnu.org/licenses/gpl.html
*
*/
;(function($){ // secure $ jQuery alias

  /**
  * Adds the ability to manage elements scroll by dragging
  * one or more of its descendant elements. Options parameter
  * allow to specifically select which inner elements will
  * respond to the drag events.
  * 
  * options properties:
  * ------------------------------------------------------------------------		
  *  dragSelector         | jquery selector to apply to each wrapped element 
  *                       | to find which will be the dragging elements. 
  *                       | Defaults to '>:first' which is the first child of 
  *                       | scrollable element
  * ------------------------------------------------------------------------		
  *  acceptPropagatedEvent| Will the dragging element accept propagated 
  *	                     | events? default is yes, a propagated mouse event 
  *	                     | on a inner element will be accepted and processed.
  *	                     | If set to false, only events originated on the
  *	                     | draggable elements will be processed.
  * ------------------------------------------------------------------------
  *  preventDefault       | Prevents the event to propagate further effectivey
  *                       | dissabling other default actions. Defaults to true
  * ------------------------------------------------------------------------
  *  
  *  usage examples:
  *
  *  To add the scroll by drag to the element id=viewport when dragging its 
  *  first child accepting any propagated events
  *	$('#viewport').dragscrollable(); 
  *
  *  To add the scroll by drag ability to any element div of class viewport
  *  when dragging its first descendant of class dragMe responding only to
  *  evcents originated on the '.dragMe' elements.
  *	$('div.viewport').dragscrollable({dragSelector:'.dragMe:first',
  *									  acceptPropagatedEvent: false});
  *
  *  Notice that some 'viewports' could be nested within others but events
  *  would not interfere as acceptPropagatedEvent is set to false.
  *		
  */
  $.fn.dragscrollable = function( options ){

    var settings = $.extend(
    {   
      dragSelector:'>:first',
      acceptPropagatedEvent: true,
      preventDefault: true
    },options || {});


    var dragscroll= {
      mouseDownHandler : function(event) {
        // mousedown, left click, check propagation
        if (event.which!=1 ||
        (!event.data.acceptPropagatedEvent && event.target != this)){ 
          return false; 
        }

        // Initial coordinates will be the last when dragging
        event.data.lastCoord = {left: event.clientX, top: event.clientY}; 

        $.event.add( document, "mouseup", 
        dragscroll.mouseUpHandler, event.data );
        $.event.add( document, "mousemove", 
        dragscroll.mouseMoveHandler, event.data );
        if (event.data.preventDefault) {
          event.preventDefault();
          return false;
        }
      },
      mouseMoveHandler : function(event) { // User is dragging
        // How much did the mouse move?
        var delta = {left: (event.clientX - event.data.lastCoord.left),
          top: (event.clientY - event.data.lastCoord.top)};

        // Set the scroll position relative to what ever the scroll is now
        event.data.scrollable.scrollLeft(
        event.data.scrollable.scrollLeft() - delta.left);
//        if ( $(document).height() < 300 )
//          {
          event.data.scrollable.scrollTop(
          event.data.scrollable.scrollTop() - delta.top);
//        }

        // Save where the cursor is
        event.data.lastCoord={left: event.clientX, top: event.clientY}
        if (event.data.preventDefault) {
          event.preventDefault();
          return false;
        }

      },
      mouseUpHandler : function(event) { // Stop scrolling
        $.event.remove( document, "mousemove", dragscroll.mouseMoveHandler);
        $.event.remove( document, "mouseup", dragscroll.mouseUpHandler);
        if (event.data.preventDefault) {
          event.preventDefault();
          return false;
        }
      }
    }

    // set up the initial events
    this.each(function() {
      // closure object data for each scrollable element
      var data = {scrollable : $(this),
        acceptPropagatedEvent : settings.acceptPropagatedEvent,
        preventDefault : settings.preventDefault }
      // Set mouse initiating event on the desired descendant
      $(this).find(settings.dragSelector).
      bind('mousedown', data, dragscroll.mouseDownHandler);
    });
  }; //end plugin dragscrollable

})( jQuery ); // confine scope