dojo.provide("dojo.dnd.autoscroll");

dojo.dnd.getViewport = function(){
	// summary: returns a viewport size (visible part of the window)
	var d = dojo.doc, dd = d.documentElement, w = window, b = dojo.body();
	if(dojo.isMozilla){
		return {w: dd.clientWidth, h: w.innerHeight};	// Object
	}else if(!dojo.isOpera && w.innerWidth){
		return {w: w.innerWidth, h: w.innerHeight};		// Object
	}else if (!dojo.isOpera && dd && dd.clientWidth){
		return {w: dd.clientWidth, h: dd.clientHeight};	// Object
	}else if (b.clientWidth){
		return {w: b.clientWidth, h: b.clientHeight};	// Object
	}
	return null;	// Object
};

dojo.dnd.V_TRIGGER_AUTOSCROLL = 32;
dojo.dnd.H_TRIGGER_AUTOSCROLL = 32;

dojo.dnd.V_AUTOSCROLL_VALUE = 16;
dojo.dnd.H_AUTOSCROLL_VALUE = 16;

dojo.dnd.autoScroll = function(e){
	// summary: a handler for onmousemove event, which scrolls the window, if necesary
	// e: Event: onmousemove event
	var v = dojo.dnd.getViewport(), dx = 0, dy = 0;
	if(e.clientX < dojo.dnd.H_TRIGGER_AUTOSCROLL){
		dx = -dojo.dnd.H_AUTOSCROLL_VALUE;
	}else if(e.clientX > v.w - dojo.dnd.H_TRIGGER_AUTOSCROLL){
		dx = dojo.dnd.H_AUTOSCROLL_VALUE;
	}
	if(e.clientY < dojo.dnd.V_TRIGGER_AUTOSCROLL){
		dy = -dojo.dnd.V_AUTOSCROLL_VALUE;
	}else if(e.clientY > v.h - dojo.dnd.V_TRIGGER_AUTOSCROLL){
		dy = dojo.dnd.V_AUTOSCROLL_VALUE;
	}
	window.scrollBy(dx, dy);
};

dojo.dnd._validNodes = {"div": 1, "p": 1, "td": 1};
dojo.dnd._validOverflow = {"auto": 1, "scroll": 1};

dojo.dnd.autoScrollNodes = function(e){
	// summary: a handler for onmousemove event, which scrolls the first avaialble Dom element,
	//	it falls back to dojo.dnd.autoScroll()
	// e: Event: onmousemove event
	for(var n = e.target; n;){
		if(n.nodeType == 1 && (n.tagName.toLowerCase() in dojo.dnd._validNodes)){
			var s = dojo.getComputedStyle(n);
			if(s.overflow.toLowerCase() in dojo.dnd._validOverflow){
				var b = dojo._getContentBox(n, s), t = dojo._abs(n, true);
				console.debug(b.l, b.t, t.x, t.y, n.scrollLeft, n.scrollTop);
				b.l += t.x + n.scrollLeft;
				b.t += t.y + n.scrollTop;
				var w = Math.min(dojo.dnd.H_TRIGGER_AUTOSCROLL, b.w / 2), 
					h = Math.min(dojo.dnd.V_TRIGGER_AUTOSCROLL, b.h / 2),
					rx = e.pageX - b.l, ry = e.pageY - b.t, dx = 0, dy = 0;
				if(rx > 0 && rx < b.w){
					if(rx < w){
						dx = -dojo.dnd.H_AUTOSCROLL_VALUE;
					}else if(rx > b.w - w){
						dx = dojo.dnd.H_AUTOSCROLL_VALUE;
					}
				}
				//console.debug("ry =", ry, "b.h =", b.h, "h =", h);
				if(ry > 0 && ry < b.h){
					if(ry < h){
						dy = -dojo.dnd.V_AUTOSCROLL_VALUE;
					}else if(ry > b.h - h){
						dy = dojo.dnd.V_AUTOSCROLL_VALUE;
					}
				}
				var oldLeft = n.scrollLeft, oldTop = n.scrollTop;
				n.scrollLeft = n.scrollLeft + dx;
				n.scrollTop  = n.scrollTop  + dy;
				if(dx || dy) console.debug(oldLeft + ", " + oldTop + "\n" + dx + ", " + dy + "\n" + n.scrollLeft + ", " + n.scrollTop);
				if(oldLeft != n.scrollLeft || oldTop != n.scrollTop){ return; }
			}
		}
		try{
			n = n.parentNode;
		}catch(x){
			n = null;
		}
	}
	dojo.dnd.autoScroll(e);
};
