/**
 * DragDrop.js
 *
 * A JavaScript micro-framework for adding drag-and-drop functionality
 * to elements for advanced UI development.
 *
 * @author     James Brumond
 * @version    0.3.0
 * @copyright  Copyright 2011 James Brumond
 * @license    Dual licensed under MIT and GPL
 */

/*jshint browser: true, bitwise: false, camelcase: false, eqnull: true, latedef: false,
  plusplus: false, jquery: true, shadow: true, smarttabs: true, loopfunc: true */

(function() {
	
	var
	
	// Is this a touch device?
	touchEvents = ('ontouchstart' in window),
	
	// A class to add when an element is being dragged
	dragClass = 'drag',
	
	/**
	 * The DragDrop namespace
	 *
	 * Example:
	 * 
	 *   DragDrop.bind ( element[, options ]);
	 *   DragDrop.unbind ( reference );
	 *
	 * @access  public
	 */
	DragDrop = (function() {
		var self = { },
		
		// Determine the events to bind to
		events = (touchEvents ?
			{
				start: 'touchstart',
				move: 'touchmove',
				end: 'touchend'
			} : {
				start: 'mousedown',
				move: 'mousemove',
				end: 'mouseup'
			}
		),
		
		// Elements already bound
		bindings = [ ],
		
		// Check if a given binding (element/anchor pair) already exists
		bindingExists = function(element, anchor) {
			for (var i = 0, c = bindings.length; i < c; i++) {
				if (bindings[i] && bindings[i].element === element && bindings[i].anchor === anchor) {
					return true;
				}
			}
			return false;
		},
		
		// Do something with a given binding's given event stack
		withBindingEvent = function(reference, event, func) {
			if (bindings[reference._id] && bindings[reference._id].events[event]) {
				func(bindings[reference._id].events[event]);
			}
		},
		
		// Parse the arguments of DragDrop.bind
		parseOptions = function(element, options) {
			options = options || { };
			options.element = element;
			options.anchor = options.anchor || element;
			options.boundingBox = options.boundingBox || null;
			options.releaseAnchors = options.releaseAnchors || [ ];
			options.releaseAnchors.unshift(document);
			return options;
		},
		
		// The next binding ID to use
		nextBinding = 1,

	// ------------------------------------------------------------------
	//  A constructor for a resource type used in referencing bindings
		
		BindingReference = function() {
			this._id = nextBinding++;
		};
		
		BindingReference.prototype.unbind = function() {
			return DragDrop.unbind(this);
		};
		
		BindingReference.prototype.bindEvent = function(event, func) {
			return DragDrop.bindEvent(this, event, func);
		};
		
		BindingReference.prototype.unbindEvent = function(event, func) {
			return DragDrop.unbindEvent(this, event, func);
		};
		
		BindingReference.prototype.invokeEvent = function(event, source) {
			return DragDrop.invokeEvent(this, event, source);
		};
		
		BindingReference.prototype.setBoundingBox = function(box) {
			bindings[this._id].boundingBox = box;
		};
		
	// ----------------------------------------------------------------------------
	//  Public Functions
		
		// Make an element draggable
		self.bind = function(element, options) {
			options = parseOptions(element, options);
			if (! isObject(options.element)) {
				throw new Error('Must give an element to drag');
			}
			if (getStyle(options.element, 'position') === 'static') {
				throw new Error('Cannot drag-drop an element with position:static');
			}
			// Check to make sure the elements aren't already bound
			if (! bindingExists(options.element, options.anchor)) {
				// Initialize the binding object
				var reference = new BindingReference();
				var binding = {
					element: options.element,
					anchor: options.anchor,
					releaseAnchors: options.releaseAnchors,
					dragging: false,
					event: null,
					shouldUnbind: false,
					boundingBox: options.boundingBox,
					events: {
						beforedrag: Callstack(options.beforedrag),
						dragstart: Callstack(options.dragstart),
						dragend: Callstack(options.dragend),
						drag: Callstack(options.drag),
						unbind: Callstack(options.unbind)
					}
				};
				// Bind the first event
				binding.event = Events.bind(binding.anchor, events.start, function(e) {
					// Make sure it's a left click or touch event
					if ((window.event && e.button === 1) || e.button === 0 || touchEvents) {
						stopEvent(e);
						// Call any "beforedrag" events before calculations begin
						binding.events.beforedrag.call(
							binding.element, new DragEvent('beforedrag', e, binding)
						);
						// Make sure everyone knows the element is being dragged
						binding.dragging = true;
						addClass(binding.element, dragClass);
						// Start calculating movement
						var startX = getPos(binding.element, 'left');
						var startY = getPos(binding.element, 'top');
						// These are used in some bounding box calculations
						var startOffsetLeft = binding.element.offsetLeft;
						var startOffsetTop = binding.element.offsetTop;
						var startTotalOffset = getOffset(binding.element);
						// A place to hold on to event functions we are going to unbind later
						var tempEvents = [ ];
						// The target for the move and end events is dependent on the input type
						var target = (touchEvents ? binding.anchor : document);
						// Bind the movement event
						tempEvents.push(Events.bind(target, events.move, function(e2) {
							// Find all needed offsets
							var offsetX = e2.clientX - e.clientX;
							var offsetY = e2.clientY - e.clientY;
							var offsetWidth = binding.element.offsetWidth;
							var offsetHeight = binding.element.offsetHeight;
							// Find the new positions
							var posX = startX + offsetX;
							var posY = startY + offsetY;
							// Enforce any bounding box
							if (binding.boundingBox) {
								var box = binding.boundingBox;
								var minX, maxX, minY, maxY;
								// Bound inside offset parent
								if (box === 'offsetParent') {
									var parent = binding.element.offsetParent;
									if (getStyle(binding.element, 'position') === 'relative') {
										minX = -startOffsetLeft;
										minY = -startOffsetTop;
									} else {
										minX = minY = 0;
									}
									maxX = parent.clientWidth + minX;
									maxY = parent.clientHeight + minY;
								}
								// Bound to the dimensions of the window
								else if (box === 'windowSize') {
									var dimensions = getWindowSize();
									if (getStyle(binding.element, 'position') === 'relative') {
										minX = -startTotalOffset.x;
										minY = -startTotalOffset.y;
									} else {
										minX = minY = 0;
									}
									maxX = dimensions.x + minX;
									maxY = dimensions.y + minY;
								}
								// Manual bounding box
								else {
									minX = box.x.min;
									maxX = box.x.max;
									minY = box.y.min;
									maxY = box.y.max;
								}
								posX = Math.max(minX, Math.min(maxX - offsetWidth, posX));
								posY = Math.max(minY, Math.min(maxY - offsetHeight, posY));
							}
							// Move the element
							binding.element.style.left = posX + 'px';
							binding.element.style.top = posY + 'px';
							// Call any "drag" events
							binding.events.drag.call(
								binding.element, new DragEvent('drag', e2, binding)
							);
							return stopEvent(e2);
						}));
						// Bind the release events
						for (var i = 0, c = binding.releaseAnchors.length; i < c; i++) {
							var elem = binding.releaseAnchors[i];
							tempEvents.push(
								Events.bind(elem, events.end, onRelease(elem))
							);
						}
						// Avoid text selection problems
						document.body.focus();
						tempEvents.push(Events.bind(document, 'selectstart', false));
						tempEvents.push(Events.bind(binding.anchor, 'dragstart', false));
						// Call any "dragstart" events
						binding.events.dragstart.call(
							binding.element, new DragEvent('dragstart', e, binding)
						);
						return false;
					}
					function onRelease(elem) {
						return function(e2) {
							// Unbind move and end events
							for (var i = 0, c = tempEvents.length; i < c; i++) {
								Events.unbind(tempEvents[i]);
							}
							// Clean up...
							binding.dragging = false;
							removeClass(binding.element, dragClass);
							if (binding.shouldUnbind) {
								DragDrop.unbind(binding.element, binding.anchor);
							}
							// Call any "dragend" events
							binding.events.dragend.call(
								binding.element, new DragEvent('dragend', e2, binding, {
									releaseAnchor: elem
								})
							);
							return stopEvent(e2);
						};
					}
				});
				// Add the binding to the list
				bindings[reference._id] = binding;
				return reference;
			}
		};
		
		// Remove an element's draggableness
		self.unbind = function(reference) {
			if (reference instanceof BindingReference) {
				var id = reference._id;
				if (bindings[id]) {
					var binding = bindings[id];

					if (binding.dragging) {
						binding.shouldUnbind = true;
					} else {
						Events.unbind(binding.event);
						bindings[id] = null;
					}
					// Call any "unbind" events
					binding.events.unbind.call(
						binding.element, new DragEvent('unbind', { target: true }, binding)
					);
				}
			}
		};
		
		// Bind a drag event
		self.bindEvent = function(reference, event, func) {
			withBindingEvent(reference, event, function(stack) {
				stack.push(func);
			});
		};
		
		// Unbind a drag event
		self.unbindEvent = function(reference, event, func) {
			withBindingEvent(reference, event, function(stack) {
				stack.remove(func);
			});
		};
		
		// Manually invoke a drag event
		self.invokeEvent = function(reference, event, source) {
			withBindingEvent(reference, event, function(stack) {
				stack.call(
					bindings[reference._id].element,
					new DragEvent(event, source, reference)
				);
			});
		};
		
		return self;
	}()),
	
// ----------------------------------------------------------------------------
//  Helper Functions
	
	// Array Remove - By John Resig (MIT Licensed)
	arrayRemove = function(array, from, to) {
		var rest = array.slice((to || from) + 1 || array.length);
		array.length = from < 0 ? array.length + from : from;
		return array.push.apply(array, rest);
	},
	
	// Get the position of an element
	getPos = function(elem, from) {
		var pos = parseFloat(getStyle(elem, from));
		return (isNaN(pos) ? 0 : pos);
	},
	
	// Get a style property from an element
	getStyle = function(elem, prop) {
		if (elem.currentStyle) {
			return elem.currentStyle[prop];
		} else if (window.getComputedStyle) {
			return document.defaultView.getComputedStyle(elem, null).getPropertyValue(prop);
		} else if (elem.style) {
			return elem.style[prop];
		}
	},
	
	// Get the dimensions of the window
	getWindowSize = function() {
		return {
			x: window.innerWidth || document.documentElement.clientWidth || body().clientWidth,
			y: window.innerHeight || document.documentElement.clientHeight || body().clientHeight
		};
	},

	// Get the total offset position of an element in the document
	getOffset = function(elem) {
		var x = 0;
		var y = 0;
		if (elem.offsetParent) {
			do {
				x += elem.offsetLeft;
				y += elem.offsetTop;
			} while (elem = elem.offsetParent);
		}
		return {x: x, y: y};
	},
	
	// Stop an event
	stopEvent = function(evt) {
		if (evt.preventDefault) {
			evt.preventDefault();
		}
		if (evt.stopPropagation) {
			evt.stopPropagation();
		}
		evt.returnValue = false;
		return false;
	},
	
	// Regular expressions for matching classnames
	cnRegexes = { },

	// Remove a class from an element
	removeClass = function(elem, cn) {
		if (! cnRegexes[cn]) {
			cnRegexes[cn] = new RegExp('(^|\\s)+' + cn + '(\\s|$)+');
		}
		elem.className = elem.className.replace(cnRegexes[cn], ' ');
	},
	
	// Add a class to an element
	addClass = function(elem, cn) {
		removeClass(elem, cn);
		elem.className += ' ' + cn;
	},
	
	// Check for a non-null object
	isObject = function(value) {
		return !! (value && typeof value === 'object');
	},

	// Gets the target property of an event
	getEventTarget = function(evt) {
		var target;
		if (evt.target) {
			target = evt.target;
		} else if (evt.srcElement) {
			target = evt.srcElement;
		}
		if (target.nodeType === 3) {
			target = target.parentNode;
		}
		return target;
	},
	
	/**
	 * A stackable function
	 *
	 * @access  private
	 * @param   function  an initial function
	 * @return  function
	 */
	Callstack = function(func) {
		var stack = [ ];
		var result = function() {
			var ret;
			for (var i = 0, c = stack.length; i < c; i++) {
				ret = stack[i].apply(this, arguments);
			}
			return ret;
		};
		result.push = function() {
			stack.push.apply(stack, arguments);
		};
		result.remove = function() {
			var args = Array.prototype.slice.call(arguments);
			var result = [ ];
			OUTER: for (var i = 0, c1 = stack.length; i < c1; i++) {
				for (var j = 0, c2 = args.length; j < c2; j++) {
					if (stack[i] === args[j]) {
						continue OUTER;
					}
				}
				result.push(stack[i]);
			}
			stack = result;
		};
		if (typeof func === 'function') {
			stack.push(func);
		}
		return result;
	},
	
	/**
	 * Custom event constructor
	 *
	 * @access  private
	 * @param   string    type
	 * @param   object    original event object
	 */
	DragEvent = function DragEvent(type, original, binding, extras) {
		this.type = type;
		this.originalEvent = original;
		this.altKey = original.altKey || false;
		this.ctrlKey = original.ctrlKey || false;
		this.shiftKey = original.shiftKey || false;
		this.timestamp = original.timestamp || (+new Date());
		this.pos = getPosition(original);
		this.binding = binding;
		this.target = getEventTarget(original);

		if (extras) {
			for (var i in extras) {
				if (extras.hasOwnProperty(i)) {
					this[i] = extras[i];
				}
			}
		}
	},
	
	/**
	 * A namespace with functions for event binding
	 *
	 * Example:
	 *
	 *   Bind
	 *    var evt = Events.bind(obj, 'event', function() { ... });
	 *
	 *   Unbind
	 *    Events.unbind(evt);
	 *     -OR-
	 *    evt.unbind();
	 *
	 * @access  private
	 */
	Events = (function() {
	
		var
	
		// Bind an event
		bindEvent = (function() {
			if (document.addEventListener) {
				return function(obj, event, func) {
					obj.addEventListener(event, func, false);
				};
			} else if (document.attachEvent) {
				return function(obj, event, func) {
					obj.attachEvent('on' + event, func);
				};
			} else {
				return function() { };
			}
		}()),
	
		// Unbind an event
		unbindEvent = (function() {
			if (document.removeEventListener) {
				return function(obj, event, func) {
					obj.removeEventListener(event, func, false);
				};
			} else if (document.detachEvent) {
				return function(obj, event, func) {
					obj.detachEvent('on' + event, func);
				};
			} else {
				return function() { };
			}
		}());
		
		// Build the return value
		return {
			bind: function(obj, event, func) {
				var oldFunc = (func === false) ? function(e) {
					return stopEvent(e);
				} : func;
				func = function(e) {
					return oldFunc.call(obj, e || window.event);
				};
				bindEvent(obj, event, func);
				var ret = function() {
					unbindEvent(obj, event, func);
				};
				ret.unbind = function() {ret();};
				return ret;
			},
			unbind: function(unbinder) {
				unbinder();
			}
		};
	
	}());
	
	function getPosition(evt) {
		var posX = 0;
		var posY = 0;
		if (evt.targetTouches) {
			posX = evt.targetTouches[0].pageX;
			posY = evt.targetTouches[0].pageY;
		} else if (evt.pageX || evt.pageY) {
			posX = evt.pageX;
			posY = evt.pageY;
		} else if (evt.clientX || evt.clientY) {
			posX = evt.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
			posY = evt.clientY + document.body.scrollTop + document.documentElement.scrollTop;
		}
		return {x: posX, y: posY};
	}
	
// ----------------------------------------------------------------------------
//  Expose
	
	window.DragDrop = DragDrop;
	
}());