(function() {

	function radToDeg(rad) {
		return rad * (180/Math.PI);
	}

	function getCenter(element) {
		var rect = element.getBoundingClientRect();
		return [
			rect.left + (rect.width / 2),
			rect.top + (rect.height / 2),
		];
	}

	function angle(vector, element) {
		var center = getCenter(element);
		var x = vector[0] - center[0];
		var y = vector[1] - center[1];
		var deg = radToDeg(Math.atan2(y, x));
		deg += 90;
		if(deg < 0) deg += 360;
		return deg;
	}

	function accessible(container) {
		if(container.tabIndex === -1) container.tabIndex = 0;
	}

	function fireEvent(element, name, rawEvent) {
		if ("createEvent" in document) {
			var event = document.createEvent("HTMLEvents");
			event.initEvent(name, false, true);
			event.raw = rawEvent;
			element.dispatchEvent(event);
		} else {
			var event = document.createEventObject();
			event.raw = rawEvent;
			element.fireEvent("on"+name, event);
		}
	}

	function angleFormInput(container) {
		var input = container.querySelector('input');
		if(!input) {
			input = document.createElement('input');
			input.type = 'hidden';
			container.appendChild(input);
		}
		return input;
	}

	function anglePivotElem(container) {
		var pivot = container.querySelector('.pivot');
		if(!pivot) {
			pivot = document.createElement('span');
			pivot.className = 'lse-knob-pivot';
			container.appendChild(pivot);
		}
		return pivot;
	}

	var defaults = {
		max: 360,
		min: 0,
		step: 1,
		name: 'angle'
	};

	function lookup(dicts) {
		return function _lookup(key) {
			for(var i = 0; i < dicts.length; i++) {
				var val = dicts[i][key];
				if(val !== undefined) return val;
			}
		}
	}

	function AngleInput($dom, options) {
		var key = lookup([$dom.dataset, options || {}, defaults]);
		var max = +key('max');
		var min = +key('min');
		var step = +key('step');
		var name = key('name');
		var value = normalize(min);

		accessible($dom);

		var $input = angleFormInput($dom);
		$input.name = name;

		var $pivot = anglePivotElem($dom);

		function normalize(degree) {
			var n = Math.max(min, Math.min(degree, max));
			var s = n - (n % step);
			var high = Math.ceil(n / step);
			var low = Math.round(n / step);
			return high >= (n / step)
				? (high * step == 360) ? 0 : (high * step)
				: low * step;
		}

		function updateView() {
			$pivot.style.transform = "rotate("+value+"deg)";
			$input.value = value;
		}

		function updateWithEvent(event, done) {
			var vector = [event.x, event.y];
			var deg = angle(vector, $dom);
			value = normalize(deg);
			updateView();

			fireEvent($dom, done ? 'change' : 'input', event);
		}

		function beginKeyboardInput() {
			var $all = document.body;

			function endKeyboardInput(e) {
				$all.removeEventListener('keydown', keyboardInput, false);
				$dom.removeEventListener('blur', endKeyboardInput, false);
			}

			var LEFT_ARROW  = 37;
			var UP_ARROW    = 38;
			var RIGHT_ARROW = 39;
			var DOWN_ARROW  = 40;

			function keyboardInput(e) {
				var dir = 0;
				switch(e.keyCode) {
					case UP_ARROW:
					case RIGHT_ARROW:
						dir = 1;
						break;
					case DOWN_ARROW:
					case LEFT_ARROW:
						dir = -1;
						break;
				}
				var val = value + (dir * step);
				if(val === max + 1) val = min;
				if(val === min - 1) val = max - 1;
				if(dir) {
					e.preventDefault();
					Angle(val);
				}
			}

			$all.addEventListener('keydown', keyboardInput, false);
			$dom.addEventListener('blur', endKeyboardInput, false);
		}

		function beginTracking(e) {
			var $all = document.body;

			function endTracking(e) {
				updateWithEvent(e, true);
				$all.removeEventListener('mousemove', duringTracking, false);
				$all.removeEventListener('mouseup', endTracking, false);
			}

			function duringTracking(e) {
				updateWithEvent(e);
			}

			$all.addEventListener('mousemove', duringTracking, false);
			$all.addEventListener('mouseup', endTracking, false);
		}

		function Angle(deg) {
			if(typeof deg === 'number') {
				value = normalize(deg);
				updateView();
				fireEvent($dom, 'change');
			}
			return value;
		}

		function attach() {
			$dom.addEventListener('focus', beginKeyboardInput, false);
			$dom.addEventListener('mousedown', beginTracking, false);
			return Angle;
		}

		function detach() {
			$dom.removeEventListener('focus', beginKeyboardInput, false);
			$dom.removeEventListener('mousedown', beginTracking, false);
			return Angle;
		}

		Angle.attach = attach;
		Angle.detach = detach;

		updateView();
		attach();
		return Angle;
	}

	if(typeof module !== 'undefined' && module.exports) {
		module.exports = AngleInput;
		try {
			var jQuery = require('jquery');
		} catch(error) {}
	} else {
		this.AngleInput = AngleInput;
	}

	if(typeof jQuery !== 'undefined' && jQuery.fn) {
		jQuery.fn.angleInput = function(options) {
			var $elems = $(this);
			$elems.each(function(index, $elem) {
				if(!$elem.angleDelegate) {
					$elem.angleDelegate = AngleInput($elem, options);
				}
			});
			return $elems;
		}

		jQuery.angleInput = function($elems, options) {
			if(typeof $elems === 'number') {
				// assume being called by $.fn.each or $.fn.map
				// angleInput(index, elem)
				$elems = $(options);
				options = null;
			}
			var elem = $elems
				.angleInput(options)
				.get(0);
			if(elem) return elem.angleDelegate;
		}
	}

}).call(this);