var selectionRect;
svg
.on( "mousedown", function() {
    var p = d3.mouse(this);
  //console.log(p);
    svg.append( "rect")
    .attrs({
        rx      : 6,
        ry      : 6,
        class   : "selection",
        x       : p[0],
        y       : p[1],
        width   : 0,
        height  : 0
    });
  //console.log(svg.select( "rect"))
})
.on( "mousemove", function() {
    var s = svg.select( "rect.selection");

    if( !s.empty()) {
        var p = d3.mouse( this),

            d = {
                x       : parseInt( s.attr( "x"), 10),
                y       : parseInt( s.attr( "y"), 10),
                width   : parseInt( s.attr( "width"), 10),
                height  : parseInt( s.attr( "height"), 10)
            },
            move = {
                x : p[0] - d.x,
                y : p[1] - d.y
            }
        ;

        if( move.x < 1 || (move.x*2<d.width)) {
            d.x = p[0];
            d.width -= move.x;
        } else {
            d.width = move.x;       
        }

        if( move.y < 1 || (move.y*2<d.height)) {
            d.y = p[1];
            d.height -= move.y;
        } else {
            d.height = move.y;       
        }
       
        s.attrs(d);
      selectionRect = d;
    }
})
.on("mouseup", function() {
    svg.select(".selection").remove();
  //console.log(selectionRect);
  if(selectionRect){
  var nodes = d3.selectAll("circle.node")["_groups"][0];
  for(var i = 0 ; i < nodes.length ; i++){
//collision detection
    if(nodes[i].attributes.cx.value >= selectionRect.x &&
      	nodes[i].attributes.cx.value <= (selectionRect.x + selectionRect.width) &&
      nodes[i].attributes.cy.value >= selectionRect.y &&
      nodes[i].attributes.cy.value <= (selectionRect.y + selectionRect.height)){
      d3.select(nodes[i]).classed("selected", true);
      selectedNodes.push(nodes[i]);
    }
    }
    console.log(selectedNodes);
  }
});

function clicked(){
           /* d3.select(this).attr('r', 25)
                .style("fill","lightcoral")
                .style("stroke","red");*/
  d3.select(this).classed("selected", !d3.select(this).classed("selected"));
  if(d3.select(this).classed("selected")){
    selectedNodes.push(this);
  }else{
    selectedNodes.splice(selectedNodes.indexOf(this), 1);
  }
  console.log(selectedNodes);
        }