/*global window: false */
/*global document: false */
"use strict";

var color = require('chartjs-color');

module.exports = function(Chart) {
	//Global Chart helpers object for utility methods and classes
	var helpers = Chart.helpers = {};

	//-- Basic js utility methods
	helpers.each = function(loopable, callback, self, reverse) {
		// Check to see if null or undefined firstly.
		var i, len;
		if (helpers.isArray(loopable)) {
			len = loopable.length;
			if (reverse) {
				for (i = len - 1; i >= 0; i--) {
					callback.call(self, loopable[i], i);
				}
			} else {
				for (i = 0; i < len; i++) {
					callback.call(self, loopable[i], i);
				}
			}
		} else if (typeof loopable === 'object') {
			var keys = Object.keys(loopable);
			len = keys.length;
			for (i = 0; i < len; i++) {
				callback.call(self, loopable[keys[i]], keys[i]);
			}
		}
	};
	helpers.clone = function(obj) {
		var objClone = {};
		helpers.each(obj, function(value, key) {
			if (helpers.isArray(value)) {
				objClone[key] = value.slice(0);
			} else if (typeof value === 'object' && value !== null) {
				objClone[key] = helpers.clone(value);
			} else {
				objClone[key] = value;
			}
		});
		return objClone;
	};
	helpers.extend = function(base) {
		var len = arguments.length;
		var additionalArgs = [];
		for (var i = 1; i < len; i++) {
			additionalArgs.push(arguments[i]);
		}
		helpers.each(additionalArgs, function(extensionObject) {
			helpers.each(extensionObject, function(value, key) {
				base[key] = value;
			});
		});
		return base;
	};
	// Need a special merge function to chart configs since they are now grouped
	helpers.configMerge = function(_base) {
		var base = helpers.clone(_base);
		helpers.each(Array.prototype.slice.call(arguments, 1), function(extension) {
			helpers.each(extension, function(value, key) {
				if (key === 'scales') {
					// Scale config merging is complex. Add out own function here for that
					base[key] = helpers.scaleMerge(base.hasOwnProperty(key) ? base[key] : {}, value);

				} else if (key === 'scale') {
					// Used in polar area & radar charts since there is only one scale
					base[key] = helpers.configMerge(base.hasOwnProperty(key) ? base[key] : {}, Chart.scaleService.getScaleDefaults(value.type), value);
				} else if (base.hasOwnProperty(key) && helpers.isArray(base[key]) && helpers.isArray(value)) {
					// In this case we have an array of objects replacing another array. Rather than doing a strict replace,
					// merge. This allows easy scale option merging
					var baseArray = base[key];

					helpers.each(value, function(valueObj, index) {

						if (index < baseArray.length) {
							if (typeof baseArray[index] === 'object' && baseArray[index] !== null && typeof valueObj === 'object' && valueObj !== null) {
								// Two objects are coming together. Do a merge of them.
								baseArray[index] = helpers.configMerge(baseArray[index], valueObj);
							} else {
								// Just overwrite in this case since there is nothing to merge
								baseArray[index] = valueObj;
							}
						} else {
							baseArray.push(valueObj); // nothing to merge
						}
					});

				} else if (base.hasOwnProperty(key) && typeof base[key] === "object" && base[key] !== null && typeof value === "object") {
					// If we are overwriting an object with an object, do a merge of the properties.
					base[key] = helpers.configMerge(base[key], value);

				} else {
					// can just overwrite the value in this case
					base[key] = value;
				}
			});
		});

		return base;
	};
	helpers.extendDeep = function(_base) {
		return _extendDeep.apply(this, arguments);

		function _extendDeep(dst) {
			helpers.each(arguments, function(obj) {
				if (obj !== dst) {
					helpers.each(obj, function(value, key) {
						if (dst[key] && dst[key].constructor && dst[key].constructor === Object) {
							_extendDeep(dst[key], value);
						} else {
							dst[key] = value;
						}
					});
				}
			});
			return dst;
		}
	};
	helpers.scaleMerge = function(_base, extension) {
		var base = helpers.clone(_base);

		helpers.each(extension, function(value, key) {
			if (key === 'xAxes' || key === 'yAxes') {
				// These properties are arrays of items
				if (base.hasOwnProperty(key)) {
					helpers.each(value, function(valueObj, index) {
						var axisType = helpers.getValueOrDefault(valueObj.type, key === 'xAxes' ? 'category' : 'linear');
						var axisDefaults = Chart.scaleService.getScaleDefaults(axisType);
						if (index >= base[key].length || !base[key][index].type) {
							base[key].push(helpers.configMerge(axisDefaults, valueObj));
						} else if (valueObj.type && valueObj.type !== base[key][index].type) {
							// Type changed. Bring in the new defaults before we bring in valueObj so that valueObj can override the correct scale defaults
							base[key][index] = helpers.configMerge(base[key][index], axisDefaults, valueObj);
						} else {
							// Type is the same
							base[key][index] = helpers.configMerge(base[key][index], valueObj);
						}
					});
				} else {
					base[key] = [];
					helpers.each(value, function(valueObj) {
						var axisType = helpers.getValueOrDefault(valueObj.type, key === 'xAxes' ? 'category' : 'linear');
						base[key].push(helpers.configMerge(Chart.scaleService.getScaleDefaults(axisType), valueObj));
					});
				}
			} else if (base.hasOwnProperty(key) && typeof base[key] === "object" && base[key] !== null && typeof value === "object") {
				// If we are overwriting an object with an object, do a merge of the properties.
				base[key] = helpers.configMerge(base[key], value);

			} else {
				// can just overwrite the value in this case
				base[key] = value;
			}
		});

		return base;
	};
	helpers.getValueAtIndexOrDefault = function(value, index, defaultValue) {
		if (value === undefined || value === null) {
			return defaultValue;
		}

		if (helpers.isArray(value)) {
			return index < value.length ? value[index] : defaultValue;
		}

		return value;
	};
	helpers.getValueOrDefault = function(value, defaultValue) {
		return value === undefined ? defaultValue : value;
	};
	helpers.indexOf = function(arrayToSearch, item) {
		if (Array.prototype.indexOf) {
			return arrayToSearch.indexOf(item);
		} else {
			for (var i = 0; i < arrayToSearch.length; i++) {
				if (arrayToSearch[i] === item)
					return i;
			}
			return -1;
		}
	};
	helpers.where = function(collection, filterCallback) {
		if (helpers.isArray(collection) && Array.prototype.filter) {
			return collection.filter(filterCallback);
		} else {
			var filtered = [];

			helpers.each(collection, function(item) {
				if (filterCallback(item)) {
					filtered.push(item);
				}
			});

			return filtered;
		}
	};
	helpers.findIndex = function(arrayToSearch, callback, thisArg) {
		var index = -1;
		if (Array.prototype.findIndex) {
			index = arrayToSearch.findIndex(callback, thisArg);
		} else {
			for (var i = 0; i < arrayToSearch.length; ++i) {
				thisArg = thisArg !== undefined ? thisArg : arrayToSearch;

				if (callback.call(thisArg, arrayToSearch[i], i, arrayToSearch)) {
					index = i;
					break;
				}
			}
		}

		return index;
	};
	helpers.findNextWhere = function(arrayToSearch, filterCallback, startIndex) {
		// Default to start of the array
		if (startIndex === undefined || startIndex === null) {
			startIndex = -1;
		}
		for (var i = startIndex + 1; i < arrayToSearch.length; i++) {
			var currentItem = arrayToSearch[i];
			if (filterCallback(currentItem)) {
				return currentItem;
			}
		}
	};
	helpers.findPreviousWhere = function(arrayToSearch, filterCallback, startIndex) {
		// Default to end of the array
		if (startIndex === undefined || startIndex === null) {
			startIndex = arrayToSearch.length;
		}
		for (var i = startIndex - 1; i >= 0; i--) {
			var currentItem = arrayToSearch[i];
			if (filterCallback(currentItem)) {
				return currentItem;
			}
		}
	};
	helpers.inherits = function(extensions) {
		//Basic javascript inheritance based on the model created in Backbone.js
		var parent = this;
		var ChartElement = (extensions && extensions.hasOwnProperty("constructor")) ? extensions.constructor : function() {
			return parent.apply(this, arguments);
		};

		var Surrogate = function() {
			this.constructor = ChartElement;
		};
		Surrogate.prototype = parent.prototype;
		ChartElement.prototype = new Surrogate();

		ChartElement.extend = helpers.inherits;

		if (extensions) {
			helpers.extend(ChartElement.prototype, extensions);
		}

		ChartElement.__super__ = parent.prototype;

		return ChartElement;
	};
	helpers.noop = function() {};
	helpers.uid = (function() {
		var id = 0;
		return function() {
			return id++;
		};
	})();
	helpers.warn = function(str) {
		//Method for warning of errors
		if (console && typeof console.warn === "function") {
			console.warn(str);
		}
	};
	//-- Math methods
	helpers.isNumber = function(n) {
		return !isNaN(parseFloat(n)) && isFinite(n);
	};
	helpers.almostEquals = function(x, y, epsilon) {
		return Math.abs(x - y) < epsilon;
	};
	helpers.max = function(array) {
		return array.reduce(function(max, value) {
			if (!isNaN(value)) {
				return Math.max(max, value);
			} else {
				return max;
			}
		}, Number.NEGATIVE_INFINITY);
	};
	helpers.min = function(array) {
		return array.reduce(function(min, value) {
			if (!isNaN(value)) {
				return Math.min(min, value);
			} else {
				return min;
			}
		}, Number.POSITIVE_INFINITY);
	};
	helpers.sign = function(x) {
		if (Math.sign) {
			return Math.sign(x);
		} else {
			x = +x; // convert to a number
			if (x === 0 || isNaN(x)) {
				return x;
			}
			return x > 0 ? 1 : -1;
		}
	};
	helpers.log10 = function(x) {
		if (Math.log10) {
			return Math.log10(x);
		} else {
			return Math.log(x) / Math.LN10;
		}
	};
	helpers.toRadians = function(degrees) {
		return degrees * (Math.PI / 180);
	};
	helpers.toDegrees = function(radians) {
		return radians * (180 / Math.PI);
	};
	// Gets the angle from vertical upright to the point about a centre.
	helpers.getAngleFromPoint = function(centrePoint, anglePoint) {
		var distanceFromXCenter = anglePoint.x - centrePoint.x,
			distanceFromYCenter = anglePoint.y - centrePoint.y,
			radialDistanceFromCenter = Math.sqrt(distanceFromXCenter * distanceFromXCenter + distanceFromYCenter * distanceFromYCenter);

		var angle = Math.atan2(distanceFromYCenter, distanceFromXCenter);

		if (angle < (-0.5 * Math.PI)) {
			angle += 2.0 * Math.PI; // make sure the returned angle is in the range of (-PI/2, 3PI/2]
		}

		return {
			angle: angle,
			distance: radialDistanceFromCenter
		};
	};
	helpers.aliasPixel = function(pixelWidth) {
		return (pixelWidth % 2 === 0) ? 0 : 0.5;
	};
	helpers.splineCurve = function(firstPoint, middlePoint, afterPoint, t) {
		//Props to Rob Spencer at scaled innovation for his post on splining between points
		//http://scaledinnovation.com/analytics/splines/aboutSplines.html

		// This function must also respect "skipped" points

		var previous = firstPoint.skip ? middlePoint : firstPoint,
			current = middlePoint,
			next = afterPoint.skip ? middlePoint : afterPoint;

		var d01 = Math.sqrt(Math.pow(current.x - previous.x, 2) + Math.pow(current.y - previous.y, 2));
		var d12 = Math.sqrt(Math.pow(next.x - current.x, 2) + Math.pow(next.y - current.y, 2));

		var s01 = d01 / (d01 + d12);
		var s12 = d12 / (d01 + d12);

		// If all points are the same, s01 & s02 will be inf
		s01 = isNaN(s01) ? 0 : s01;
		s12 = isNaN(s12) ? 0 : s12;

		var fa = t * s01; // scaling factor for triangle Ta
		var fb = t * s12;

		return {
			previous: {
				x: current.x - fa * (next.x - previous.x),
				y: current.y - fa * (next.y - previous.y)
			},
			next: {
				x: current.x + fb * (next.x - previous.x),
				y: current.y + fb * (next.y - previous.y)
			}
		};
	};
	helpers.nextItem = function(collection, index, loop) {
		if (loop) {
			return index >= collection.length - 1 ? collection[0] : collection[index + 1];
		}

		return index >= collection.length - 1 ? collection[collection.length - 1] : collection[index + 1];
	};
	helpers.previousItem = function(collection, index, loop) {
		if (loop) {
			return index <= 0 ? collection[collection.length - 1] : collection[index - 1];
		}
		return index <= 0 ? collection[0] : collection[index - 1];
	};
	// Implementation of the nice number algorithm used in determining where axis labels will go
	helpers.niceNum = function(range, round) {
		var exponent = Math.floor(helpers.log10(range));
		var fraction = range / Math.pow(10, exponent);
		var niceFraction;

		if (round) {
			if (fraction < 1.5) {
				niceFraction = 1;
			} else if (fraction < 3) {
				niceFraction = 2;
			} else if (fraction < 7) {
				niceFraction = 5;
			} else {
				niceFraction = 10;
			}
		} else {
			if (fraction <= 1.0) {
				niceFraction = 1;
			} else if (fraction <= 2) {
				niceFraction = 2;
			} else if (fraction <= 5) {
				niceFraction = 5;
			} else {
				niceFraction = 10;
			}
		}

		return niceFraction * Math.pow(10, exponent);
	};
	//Easing functions adapted from Robert Penner's easing equations
	//http://www.robertpenner.com/easing/
	var easingEffects = helpers.easingEffects = {
		linear: function(t) {
			return t;
		},
		easeInQuad: function(t) {
			return t * t;
		},
		easeOutQuad: function(t) {
			return -1 * t * (t - 2);
		},
		easeInOutQuad: function(t) {
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * t * t;
			}
			return -1 / 2 * ((--t) * (t - 2) - 1);
		},
		easeInCubic: function(t) {
			return t * t * t;
		},
		easeOutCubic: function(t) {
			return 1 * ((t = t / 1 - 1) * t * t + 1);
		},
		easeInOutCubic: function(t) {
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * t * t * t;
			}
			return 1 / 2 * ((t -= 2) * t * t + 2);
		},
		easeInQuart: function(t) {
			return t * t * t * t;
		},
		easeOutQuart: function(t) {
			return -1 * ((t = t / 1 - 1) * t * t * t - 1);
		},
		easeInOutQuart: function(t) {
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * t * t * t * t;
			}
			return -1 / 2 * ((t -= 2) * t * t * t - 2);
		},
		easeInQuint: function(t) {
			return 1 * (t /= 1) * t * t * t * t;
		},
		easeOutQuint: function(t) {
			return 1 * ((t = t / 1 - 1) * t * t * t * t + 1);
		},
		easeInOutQuint: function(t) {
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * t * t * t * t * t;
			}
			return 1 / 2 * ((t -= 2) * t * t * t * t + 2);
		},
		easeInSine: function(t) {
			return -1 * Math.cos(t / 1 * (Math.PI / 2)) + 1;
		},
		easeOutSine: function(t) {
			return 1 * Math.sin(t / 1 * (Math.PI / 2));
		},
		easeInOutSine: function(t) {
			return -1 / 2 * (Math.cos(Math.PI * t / 1) - 1);
		},
		easeInExpo: function(t) {
			return (t === 0) ? 1 : 1 * Math.pow(2, 10 * (t / 1 - 1));
		},
		easeOutExpo: function(t) {
			return (t === 1) ? 1 : 1 * (-Math.pow(2, -10 * t / 1) + 1);
		},
		easeInOutExpo: function(t) {
			if (t === 0) {
				return 0;
			}
			if (t === 1) {
				return 1;
			}
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * Math.pow(2, 10 * (t - 1));
			}
			return 1 / 2 * (-Math.pow(2, -10 * --t) + 2);
		},
		easeInCirc: function(t) {
			if (t >= 1) {
				return t;
			}
			return -1 * (Math.sqrt(1 - (t /= 1) * t) - 1);
		},
		easeOutCirc: function(t) {
			return 1 * Math.sqrt(1 - (t = t / 1 - 1) * t);
		},
		easeInOutCirc: function(t) {
			if ((t /= 1 / 2) < 1) {
				return -1 / 2 * (Math.sqrt(1 - t * t) - 1);
			}
			return 1 / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1);
		},
		easeInElastic: function(t) {
			var s = 1.70158;
			var p = 0;
			var a = 1;
			if (t === 0) {
				return 0;
			}
			if ((t /= 1) === 1) {
				return 1;
			}
			if (!p) {
				p = 1 * 0.3;
			}
			if (a < Math.abs(1)) {
				a = 1;
				s = p / 4;
			} else {
				s = p / (2 * Math.PI) * Math.asin(1 / a);
			}
			return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * 1 - s) * (2 * Math.PI) / p));
		},
		easeOutElastic: function(t) {
			var s = 1.70158;
			var p = 0;
			var a = 1;
			if (t === 0) {
				return 0;
			}
			if ((t /= 1) === 1) {
				return 1;
			}
			if (!p) {
				p = 1 * 0.3;
			}
			if (a < Math.abs(1)) {
				a = 1;
				s = p / 4;
			} else {
				s = p / (2 * Math.PI) * Math.asin(1 / a);
			}
			return a * Math.pow(2, -10 * t) * Math.sin((t * 1 - s) * (2 * Math.PI) / p) + 1;
		},
		easeInOutElastic: function(t) {
			var s = 1.70158;
			var p = 0;
			var a = 1;
			if (t === 0) {
				return 0;
			}
			if ((t /= 1 / 2) === 2) {
				return 1;
			}
			if (!p) {
				p = 1 * (0.3 * 1.5);
			}
			if (a < Math.abs(1)) {
				a = 1;
				s = p / 4;
			} else {
				s = p / (2 * Math.PI) * Math.asin(1 / a);
			}
			if (t < 1) {
				return -0.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * 1 - s) * (2 * Math.PI) / p));
			}
			return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * 1 - s) * (2 * Math.PI) / p) * 0.5 + 1;
		},
		easeInBack: function(t) {
			var s = 1.70158;
			return 1 * (t /= 1) * t * ((s + 1) * t - s);
		},
		easeOutBack: function(t) {
			var s = 1.70158;
			return 1 * ((t = t / 1 - 1) * t * ((s + 1) * t + s) + 1);
		},
		easeInOutBack: function(t) {
			var s = 1.70158;
			if ((t /= 1 / 2) < 1) {
				return 1 / 2 * (t * t * (((s *= (1.525)) + 1) * t - s));
			}
			return 1 / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2);
		},
		easeInBounce: function(t) {
			return 1 - easingEffects.easeOutBounce(1 - t);
		},
		easeOutBounce: function(t) {
			if ((t /= 1) < (1 / 2.75)) {
				return 1 * (7.5625 * t * t);
			} else if (t < (2 / 2.75)) {
				return 1 * (7.5625 * (t -= (1.5 / 2.75)) * t + 0.75);
			} else if (t < (2.5 / 2.75)) {
				return 1 * (7.5625 * (t -= (2.25 / 2.75)) * t + 0.9375);
			} else {
				return 1 * (7.5625 * (t -= (2.625 / 2.75)) * t + 0.984375);
			}
		},
		easeInOutBounce: function(t) {
			if (t < 1 / 2) {
				return easingEffects.easeInBounce(t * 2) * 0.5;
			}
			return easingEffects.easeOutBounce(t * 2 - 1) * 0.5 + 1 * 0.5;
		}
	};
	//Request animation polyfill - http://www.paulirish.com/2011/requestanimationframe-for-smart-animating/
	helpers.requestAnimFrame = (function() {
		return window.requestAnimationFrame ||
			window.webkitRequestAnimationFrame ||
			window.mozRequestAnimationFrame ||
			window.oRequestAnimationFrame ||
			window.msRequestAnimationFrame ||
			function(callback) {
				return window.setTimeout(callback, 1000 / 60);
			};
	})();
	helpers.cancelAnimFrame = (function() {
		return window.cancelAnimationFrame ||
			window.webkitCancelAnimationFrame ||
			window.mozCancelAnimationFrame ||
			window.oCancelAnimationFrame ||
			window.msCancelAnimationFrame ||
			function(callback) {
				return window.clearTimeout(callback, 1000 / 60);
			};
	})();
	//-- DOM methods
	helpers.getRelativePosition = function(evt, chart) {
		var mouseX, mouseY;
		var e = evt.originalEvent || evt,
			canvas = evt.currentTarget || evt.srcElement,
			boundingRect = canvas.getBoundingClientRect();

		var touches = e.touches;
		if (touches && touches.length > 0) {
			mouseX = touches[0].clientX;
			mouseY = touches[0].clientY;

		} else {
			mouseX = e.clientX;
			mouseY = e.clientY;
		}

		// Scale mouse coordinates into canvas coordinates
		// by following the pattern laid out by 'jerryj' in the comments of
		// http://www.html5canvastutorials.com/advanced/html5-canvas-mouse-coordinates/
		var paddingLeft = parseFloat(helpers.getStyle(canvas, 'padding-left'));
		var paddingTop = parseFloat(helpers.getStyle(canvas, 'padding-top'));
		var paddingRight = parseFloat(helpers.getStyle(canvas, 'padding-right'));
		var paddingBottom = parseFloat(helpers.getStyle(canvas, 'padding-bottom'));
		var width = boundingRect.right - boundingRect.left - paddingLeft - paddingRight;
		var height = boundingRect.bottom - boundingRect.top - paddingTop - paddingBottom;

		// We divide by the current device pixel ratio, because the canvas is scaled up by that amount in each direction. However
		// the backend model is in unscaled coordinates. Since we are going to deal with our model coordinates, we go back here
		mouseX = Math.round((mouseX - boundingRect.left - paddingLeft) / (width) * canvas.width / chart.currentDevicePixelRatio);
		mouseY = Math.round((mouseY - boundingRect.top - paddingTop) / (height) * canvas.height / chart.currentDevicePixelRatio);

		return {
			x: mouseX,
			y: mouseY
		};

	};
	helpers.addEvent = function(node, eventType, method) {
		if (node.addEventListener) {
			node.addEventListener(eventType, method);
		} else if (node.attachEvent) {
			node.attachEvent("on" + eventType, method);
		} else {
			node["on" + eventType] = method;
		}
	};
	helpers.removeEvent = function(node, eventType, handler) {
		if (node.removeEventListener) {
			node.removeEventListener(eventType, handler, false);
		} else if (node.detachEvent) {
			node.detachEvent("on" + eventType, handler);
		} else {
			node["on" + eventType] = helpers.noop;
		}
	};
	helpers.bindEvents = function(chartInstance, arrayOfEvents, handler) {
		// Create the events object if it's not already present
		var events = chartInstance.events = chartInstance.events || {};

		helpers.each(arrayOfEvents, function(eventName) {
			events[eventName] = function() {
				handler.apply(chartInstance, arguments);
			};
			helpers.addEvent(chartInstance.chart.canvas, eventName, events[eventName]);
		});
	};
	helpers.unbindEvents = function(chartInstance, arrayOfEvents) {
		var canvas = chartInstance.chart.canvas;
		helpers.each(arrayOfEvents, function(handler, eventName) {
			helpers.removeEvent(canvas, eventName, handler);
		});
	};

	// Private helper function to convert max-width/max-height values that may be percentages into a number
	function parseMaxStyle(styleValue, node, parentProperty) {
		var valueInPixels;
		if (typeof(styleValue) === 'string') {
			valueInPixels = parseInt(styleValue, 10);

			if (styleValue.indexOf('%') != -1) {
				// percentage * size in dimension
				valueInPixels = valueInPixels / 100 * node.parentNode[parentProperty];
			}
		} else {
			valueInPixels = styleValue;
		}

		return valueInPixels;
	}

	/**
	 * Returns if the given value contains an effective constraint.
	 * @private
	 */
	function isConstrainedValue(value) {
		return value !== undefined &&  value !== null && value !== 'none';
	}

	// Private helper to get a constraint dimension
	// @param domNode : the node to check the constraint on
	// @param maxStyle : the style that defines the maximum for the direction we are using (maxWidth / maxHeight)
	// @param percentageProperty : property of parent to use when calculating width as a percentage
	// @see http://www.nathanaeljones.com/blog/2013/reading-max-width-cross-browser
	function getConstraintDimension(domNode, maxStyle, percentageProperty) {
		var view = document.defaultView;
		var parentNode = domNode.parentNode;
		var constrainedNode = view.getComputedStyle(domNode)[maxStyle];
		var constrainedContainer = view.getComputedStyle(parentNode)[maxStyle];
		var hasCNode = isConstrainedValue(constrainedNode);
		var hasCContainer = isConstrainedValue(constrainedContainer);
		var infinity = Number.POSITIVE_INFINITY;

		if (hasCNode || hasCContainer) {
			return Math.min(
				hasCNode? parseMaxStyle(constrainedNode, domNode, percentageProperty) : infinity,
				hasCContainer? parseMaxStyle(constrainedContainer, parentNode, percentageProperty) : infinity);
		}

		return 'none';
	}
	// returns Number or undefined if no constraint
	helpers.getConstraintWidth = function(domNode) {
		return getConstraintDimension(domNode, 'max-width', 'clientWidth');
	};
	// returns Number or undefined if no constraint
	helpers.getConstraintHeight = function(domNode) {
		return getConstraintDimension(domNode, 'max-height', 'clientHeight');
	};
	helpers.getMaximumWidth = function(domNode) {
		var container = domNode.parentNode;
		var padding = parseInt(helpers.getStyle(container, 'padding-left')) + parseInt(helpers.getStyle(container, 'padding-right'));
		var w = container.clientWidth - padding;
		var cw = helpers.getConstraintWidth(domNode);
		return isNaN(cw)? w : Math.min(w, cw);
	};
	helpers.getMaximumHeight = function(domNode) {
		var container = domNode.parentNode;
		var padding = parseInt(helpers.getStyle(container, 'padding-top')) + parseInt(helpers.getStyle(container, 'padding-bottom'));
		var h = container.clientHeight - padding;
		var ch = helpers.getConstraintHeight(domNode);
		return isNaN(ch)? h : Math.min(h, ch);
	};
	helpers.getStyle = function(el, property) {
		return el.currentStyle ?
			el.currentStyle[property] :
			document.defaultView.getComputedStyle(el, null).getPropertyValue(property);
	};
	helpers.retinaScale = function(chart) {
		var ctx = chart.ctx;
		var canvas = chart.canvas;
		var width = canvas.width;
		var height = canvas.height;
		var pixelRatio = chart.currentDevicePixelRatio = window.devicePixelRatio || 1;

		if (pixelRatio !== 1) {
			canvas.height = height * pixelRatio;
			canvas.width = width * pixelRatio;
			ctx.scale(pixelRatio, pixelRatio);

			// Store the device pixel ratio so that we can go backwards in `destroy`.
			// The devicePixelRatio changes with zoom, so there are no guarantees that it is the same
			// when destroy is called
			chart.originalDevicePixelRatio = chart.originalDevicePixelRatio || pixelRatio;
		}

		canvas.style.width = width + 'px';
		canvas.style.height = height + 'px';
	};
	//-- Canvas methods
	helpers.clear = function(chart) {
		chart.ctx.clearRect(0, 0, chart.width, chart.height);
	};
	helpers.fontString = function(pixelSize, fontStyle, fontFamily) {
		return fontStyle + " " + pixelSize + "px " + fontFamily;
	};
	helpers.longestText = function(ctx, font, arrayOfStrings, cache) {
		cache = cache || {};
		var data = cache.data = cache.data || {};
		var gc = cache.garbageCollect = cache.garbageCollect || [];

		if (cache.font !== font) {
			data = cache.data = {};
			gc = cache.garbageCollect = [];
			cache.font = font;
		}

		ctx.font = font;
		var longest = 0;
		helpers.each(arrayOfStrings, function(string) {
			// Undefined strings should not be measured
			if (string !== undefined && string !== null) {
				var textWidth = data[string];
				if (!textWidth) {
					textWidth = data[string] = ctx.measureText(string).width;
					gc.push(string);
				}

				if (textWidth > longest) {
					longest = textWidth;
				}
			}
		});

		var gcLen = gc.length / 2;
		if (gcLen > arrayOfStrings.length) {
			for (var i = 0; i < gcLen; i++) {
				delete data[gc[i]];
			}
			gc.splice(0, gcLen);
		}

		return longest;
	};
	helpers.drawRoundedRectangle = function(ctx, x, y, width, height, radius) {
		ctx.beginPath();
		ctx.moveTo(x + radius, y);
		ctx.lineTo(x + width - radius, y);
		ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
		ctx.lineTo(x + width, y + height - radius);
		ctx.quadraticCurveTo(x + width, y + height, x + width - radius, y + height);
		ctx.lineTo(x + radius, y + height);
		ctx.quadraticCurveTo(x, y + height, x, y + height - radius);
		ctx.lineTo(x, y + radius);
		ctx.quadraticCurveTo(x, y, x + radius, y);
		ctx.closePath();
	};
	helpers.color = function(c) {
		if (!color) {
			console.log('Color.js not found!');
			return c;
		}

		/* global CanvasGradient */
		if (c instanceof CanvasGradient) {
			return color(Chart.defaults.global.defaultColor);
		}

		return color(c);
	};
	helpers.addResizeListener = function(node, callback) {
		// Hide an iframe before the node
		var hiddenIframe = document.createElement('iframe');
		var hiddenIframeClass = 'chartjs-hidden-iframe';

		if (hiddenIframe.classlist) {
			// can use classlist
			hiddenIframe.classlist.add(hiddenIframeClass);
		} else {
			hiddenIframe.setAttribute('class', hiddenIframeClass);
		}

		// Set the style
		var style = hiddenIframe.style;
		style.width = '100%';
		style.display = 'block';
		style.border = 0;
		style.height = 0;
		style.margin = 0;
		style.position = 'absolute';
		style.left = 0;
		style.right = 0;
		style.top = 0;
		style.bottom = 0;

		// Insert the iframe so that contentWindow is available
		node.insertBefore(hiddenIframe, node.firstChild);

		(hiddenIframe.contentWindow || hiddenIframe).onresize = function() {
			if (callback) {
				callback();
			}
		};
	};
	helpers.removeResizeListener = function(node) {
		var hiddenIframe = node.querySelector('.chartjs-hidden-iframe');

		// Remove the resize detect iframe
		if (hiddenIframe) {
			hiddenIframe.parentNode.removeChild(hiddenIframe);
		}
	};
	helpers.isArray = function(obj) {
		if (!Array.isArray) {
			return Object.prototype.toString.call(obj) === '[object Array]';
		}
		return Array.isArray(obj);
	};
	//! @see http://stackoverflow.com/a/14853974
	helpers.arrayEquals = function(a0, a1) {
		var i, ilen, v0, v1;

		if (!a0 || !a1 || a0.length != a1.length) {
			return false;
		}

		for (i = 0, ilen=a0.length; i < ilen; ++i) {
			v0 = a0[i];
			v1 = a1[i];

			if (v0 instanceof Array && v1 instanceof Array) {
				if (!helpers.arrayEquals(v0, v1)) {
					return false;
				}
			} else if (v0 != v1) {
				// NOTE: two different object instances will never be equal: {x:20} != {x:20}
				return false;
			}
		}

		return true;
	};
	helpers.pushAllIfDefined = function(element, array) {
		if (typeof element === "undefined") {
			return;
		}

		if (helpers.isArray(element)) {
			array.push.apply(array, element);
		} else {
			array.push(element);
		}
	};
	helpers.callCallback = function(fn, args, _tArg) {
		if (fn && typeof fn.call === 'function') {
			fn.apply(_tArg, args);
		}
	};
	helpers.getHoverColor = function(color) {
		/* global CanvasPattern */
		return (color instanceof CanvasPattern) ?
			color :
			helpers.color(color).saturate(0.5).darken(0.1).rgbString();
	};
};
