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

dojo.require("dojo.dnd.common");
dojo.require("dojo.dnd.autoscroll");

dojo.declare("dojo.dnd.Mover", null, {
	constructor: function(node, e, host){
		// summary: an object, which makes a node follow the mouse, 
		//	used as a default mover, and as a base class for custom movers
		// node: Node: a node (or node's id) to be moved
		// e: Event: a mouse event, which started the move;
		//	only pageX and pageY properties are used
		// host: Object?: object which implements the functionality of the move,
		//	 and defines proper events (onMoveStart and onMoveStop)
		this.node = dojo.byId(node);
		this.marginBox = {l: e.pageX, t: e.pageY};
		this.mouseButton = e.button;
		var h = this.host = host, d = node.ownerDocument, 
			firstEvent = dojo.connect(d, "onmousemove", this, "onFirstMove");
		this.events = [
			dojo.connect(d, "onmousemove", this, "onMouseMove"),
			dojo.connect(d, "onmouseup",   this, "onMouseUp"),
			// cancel text selection and text dragging
			dojo.connect(d, "ondragstart",   dojo.stopEvent),
			dojo.connect(d.body, "onselectstart", dojo.stopEvent),
			firstEvent
		];
		// notify that the move has started
		if(h && h.onMoveStart){
			h.onMoveStart(this);
		}
	},
	// mouse event processors
	onMouseMove: function(e){
		// summary: event processor for onmousemove
		// e: Event: mouse event
		dojo.dnd.autoScroll(e);
		var m = this.marginBox;
		this.host.onMove(this, {l: m.l + e.pageX, t: m.t + e.pageY});
		dojo.stopEvent(e);
	},
	onMouseUp: function(e){
		if(dojo.isWebKit && dojo.dnd._isMac && this.mouseButton == 2 ? 
				e.button == 0 : this.mouseButton == e.button){
			this.destroy();
		}
		dojo.stopEvent(e);
	},
	// utilities
	onFirstMove: function(){
		// summary: makes the node absolute; it is meant to be called only once. 
		// 	relative and absolutely positioned nodes are assumed to use pixel units
		var s = this.node.style, l, t, h = this.host;
		switch(s.position){
			case "relative":
			case "absolute":
				// assume that left and top values are in pixels already
				l = Math.round(parseFloat(s.left));
				t = Math.round(parseFloat(s.top));
				break;
			default:
				s.position = "absolute";	// enforcing the absolute mode
				var m = dojo.marginBox(this.node);
				// event.pageX/pageY (which we used to generate the initial
				// margin box) includes padding and margin set on the body.
				// However, setting the node's position to absolute and then
				// doing dojo.marginBox on it *doesn't* take that additional
				// space into account - so we need to subtract the combined
				// padding and margin.  We use getComputedStyle and
				// _getMarginBox/_getContentBox to avoid the extra lookup of
				// the computed style. 
				var b = dojo.doc.body;
				var bs = dojo.getComputedStyle(b);
				var bm = dojo._getMarginBox(b, bs);
				var bc = dojo._getContentBox(b, bs);
				l = m.l - (bc.l - bm.l);
				t = m.t - (bc.t - bm.t);
				break;
		}
		this.marginBox.l = l - this.marginBox.l;
		this.marginBox.t = t - this.marginBox.t;
		if(h && h.onFirstMove){
			h.onFirstMove(this);
		}
		dojo.disconnect(this.events.pop());
	},
	destroy: function(){
		// summary: stops the move, deletes all references, so the object can be garbage-collected
		dojo.forEach(this.events, dojo.disconnect);
		// undo global settings
		var h = this.host;
		if(h && h.onMoveStop){
			h.onMoveStop(this);
		}
		// destroy objects
		this.events = this.node = this.host = null;
	}
});