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

 // comments by Pavel Publichenko (2007-2010)

/**********************************************************
 Further modified from the example by Tim Taylor
 http://tool-man.org/examples/sorting.html
 
 Changed onMouseMove where it calls group.onDrag and then
 adjusts the offset for changes to the DOM.  If the item
 being moved changed parents it would be off so changed to
 get the absolute offset (recursive northwestOffset).
 
 **********************************************************/

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(); // вызываем в Drag.onMouseDown, переопределяем как DragDrop.onDragStart
		group.onDragEnd = new Function(); // вызываем в Drag.onMouseUp, переопределяем как DragDrop.onDragEnd
		group.onDrag = new Function(); // вызываем в Drag.onMouseMove, переопределяем как DragDrop.onDrag
		
		// 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; // начинается всё отсюда
	},

	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;  // тупо используем event.clientX, event.clientY

		var nwPosition = Coordinates.northwestPosition(group); // для position:absolute определяется неправильно (element.style.left)
		var sePosition = Coordinates.southeastPosition(group); // для position:absolute определяется неправильно

		var nwOffset = Coordinates.northwestOffset(group, true); // испоользуем element.offsetLeft, element.offsetTop
		var seOffset = Coordinates.southeastOffset(group, true); // для перетаскивания Drag не используется, можно написать nwOffset = Coordinates.ORIGIN;

		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; // запоминаем текущие коорд. мыши

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

		group.onDragStart(nwPosition, sePosition, nwOffset, seOffset); // используется только для DragDrop

		// 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 (top left) pos: " + nwPosition.toString() + "    " + 
				"SE (bottom right) 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); // если заданы границы перетаскивания, координаты мыши корректируются
		// Посетитель обычно кликает не в левый-верхний угол, а куда угодно на элементе.
		// Поэтому чтобы элемент не прилипал к курсору верхним-левым углом, к позиции элемента необходимо добавить смещение мыши на момент клика.
		nwPosition = nwPosition.plus(adjusted.minus(group.dragCoordinate));  // [left,top] + ([новые коорд. мыши] - [старые коорд. мыши])
		nwPosition.reposition(group); // !!! тут изменяем координаты 	element.style["top"] = this.y + "px";	element.style["left"] = this.x + "px";

		group.dragCoordinate = adjusted;  // записываем новые координаты мыши

		// 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
		
		// changed to be recursive/use absolute offset for corrections
		var offsetBefore = Coordinates.northwestOffset(group, true);
		group.onDrag(nwPosition, sePosition, nwOffset, seOffset); // используется только для DragDrop
		var offsetAfter = Coordinates.northwestOffset(group, true);

		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;
		}

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

		return false;
	},

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

		return event;
	}
};