/*
 * drag.js - click & drag DOM elements
 *
 * originally based on Youngpup's dom-drag.js, www.youngpup.net
 */

var Drag = {
	BIG_Z_INDEX : 10000,
	group : null,
	isDragging : false,

	makeDraggable : function(group) {
		group.handle = group;
		group.handle.group = group;

		group.minX = null;
		group.minY = null;
		group.maxX = null;
		group.maxY = null;
		group.threshold = 0;
		group.thresholdY = 0;
		group.thresholdX = 0;

		group.onDragStart = new Function();
		group.onDragEnd = new Function();
		group.onDrag = new Function();
		
		// TODO: use element.prototype.myFunc
		group.setDragHandle = Drag.setDragHandle;
		group.setDragThreshold = Drag.setDragThreshold;
		group.setDragThresholdX = Drag.setDragThresholdX;
		group.setDragThresholdY = Drag.setDragThresholdY;
		group.constrain = Drag.constrain;
		group.constrainVertical = Drag.constrainVertical;
		group.constrainHorizontal = Drag.constrainHorizontal;

		group.onmousedown = Drag.onMouseDown;
	},

	constrainVertical : function() {
		var nwOffset = Coordinates.northwestOffset(this, true);
		this.minX = nwOffset.x;
		this.maxX = nwOffset.x;
	},

	constrainHorizontal : function() {
		var nwOffset = Coordinates.northwestOffset(this, true);
		this.minY = nwOffset.y;
		this.maxY = nwOffset.y;
	},

	constrain : function(nwPosition, sePosition) {
		this.minX = nwPosition.x;
		this.minY = nwPosition.y;
		this.maxX = sePosition.x;
		this.maxY = sePosition.y;
	},

	setDragHandle : function(handle) {
		if (handle && handle != null) 
			this.handle = handle;
		else
			this.handle = this;

		this.handle.group = this;
		this.onmousedown = null;
		this.handle.onmousedown = Drag.onMouseDown;
	},

	setDragThreshold : function(threshold) {
		if (isNaN(parseInt(threshold))) return;

		this.threshold = threshold;
	},

	setDragThresholdX : function(threshold) {
		if (isNaN(parseInt(threshold))) return;

		this.thresholdX = threshold;
	},

	setDragThresholdY : function(threshold) {
		if (isNaN(parseInt(threshold))) return;

		this.thresholdY = threshold;
	},

	onMouseDown : function(event) {
		event = Drag.fixEvent(event);
		Drag.group = this.group;

		var group = this.group;
		var mouse = event.windowCoordinate;
		var nwOffset = Coordinates.northwestOffset(group, true);
		var nwPosition = Coordinates.northwestPosition(group);
		var sePosition = Coordinates.southeastPosition(group);
		var seOffset = Coordinates.southeastOffset(group, true);

		group.originalOpacity = group.style.opacity;
		group.originalZIndex = group.style.zIndex;
		group.initialWindowCoordinate = mouse;
		// TODO: need a better name, but don't yet understand how it
		// participates in the magic while dragging 
		group.dragCoordinate = mouse;

		Drag.showStatus(mouse, nwPosition, sePosition, nwOffset, seOffset);

		group.onDragStart(nwPosition, sePosition, nwOffset, seOffset);

		// TODO: need better constraint API
		if (group.minX != null)
			group.minMouseX = mouse.x - nwPosition.x + 
					group.minX - nwOffset.x;
		if (group.maxX != null) 
			group.maxMouseX = group.minMouseX + group.maxX - group.minX;

		if (group.minY != null)
			group.minMouseY = mouse.y - nwPosition.y + 
					group.minY - nwOffset.y;
		if (group.maxY != null) 
			group.maxMouseY = group.minMouseY + group.maxY - group.minY;

		group.mouseMin = new Coordinate(group.minMouseX, group.minMouseY);
		group.mouseMax = new Coordinate(group.maxMouseX, group.maxMouseY);

		document.onmousemove = Drag.onMouseMove;
		document.onmouseup = Drag.onMouseUp;

		return false;
	},

	showStatus : function(mouse, nwPosition, sePosition, nwOffset, seOffset) {
		window.status = 
				"mouse: " + mouse.toString() + "    " + 
				"NW pos: " + nwPosition.toString() + "    " + 
				"SE pos: " + sePosition.toString() + "    " + 
				"NW offset: " + nwOffset.toString() + "    " +
				"SE offset: " + seOffset.toString();
	},

	onMouseMove : function(event) {
		event = Drag.fixEvent(event);
		var group = Drag.group;
		var mouse = event.windowCoordinate;
		var nwOffset = Coordinates.northwestOffset(group, true);
		var nwPosition = Coordinates.northwestPosition(group);
		var sePosition = Coordinates.southeastPosition(group);
		var seOffset = Coordinates.southeastOffset(group, true);

		Drag.showStatus(mouse, nwPosition, sePosition, nwOffset, seOffset);

		if (!Drag.isDragging) {
			if (group.threshold > 0) {
				var distance = group.initialWindowCoordinate.distance(
						mouse);
				if (distance < group.threshold) return true;
			} else if (group.thresholdY > 0) {
				var deltaY = Math.abs(group.initialWindowCoordinate.y - mouse.y);
				if (deltaY < group.thresholdY) return true;
			} else if (group.thresholdX > 0) {
				var deltaX = Math.abs(group.initialWindowCoordinate.x - mouse.x);
				if (deltaX < group.thresholdX) return true;
			}

			Drag.isDragging = true;
			group.style["zIndex"] = Drag.BIG_Z_INDEX;
			group.style["opacity"] = 0.75;
		}

		// TODO: need better constraint API
		var adjusted = mouse.constrain(group.mouseMin, group.mouseMax);
		nwPosition = nwPosition.plus(adjusted.minus(group.dragCoordinate));
		nwPosition.reposition(group);
		group.dragCoordinate = adjusted;

		// once dragging has started, the position of the group
		// relative to the mouse should stay fixed.  They can get out
		// of sync if the DOM is manipulated while dragging, so we
		// correct the error here
		//
		// TODO: what we really want to do is find the offset from
		// our corner to the mouse coordinate and adjust to keep it
		// the same
		var offsetBefore = Coordinates.northwestOffset(group);
		group.onDrag(nwPosition, sePosition, nwOffset, seOffset);
		var offsetAfter = Coordinates.northwestOffset(group);

		if (!offsetBefore.equals(offsetAfter)) {
			var errorDelta = offsetBefore.minus(offsetAfter);
			nwPosition = Coordinates.northwestPosition(group).plus(errorDelta);
			nwPosition.reposition(group);
		}

		return false;
	},

	onMouseUp : function(event) {
		event = Drag.fixEvent(event);
		var group = Drag.group;

		var mouse = event.windowCoordinate;
		var nwOffset = Coordinates.northwestOffset(group, true);
		var nwPosition = Coordinates.northwestPosition(group);
		var sePosition = Coordinates.southeastPosition(group);
		var seOffset = Coordinates.southeastOffset(group, true);

		document.onmousemove = null;
		document.onmouseup   = null;
		group.onDragEnd(nwPosition, sePosition, nwOffset, seOffset);

		if (Drag.isDragging) {
			// restoring zIndex before opacity avoids visual flicker in Firefox
			group.style["zIndex"] = group.originalZIndex;
			group.style["opacity"] = group.originalOpacity;
		}

		// call dragEnd() in main Script
		dragEnd(group);

		Drag.group = null;
		Drag.isDragging = false;

		return false;
	},

	fixEvent : function(event) {
		if (typeof event == 'undefined') event = window.event;
		Coordinates.fixEvent(event);

		return event;
	}
};
