(function (root, factory) {
	if ( typeof define === 'function' && define.amd ) {
		define([], function () {
			return factory(root);
		});
	} else if ( typeof exports === 'object' ) {
		module.exports = factory(root);
	} else {
		root.SmoothScroll = factory(root);
	}
})(typeof global !== 'undefined' ? global : typeof window !== 'undefined' ? window : this, function (window) {

	'use strict';

	//
	// Feature Test
	//

	var supports =
		'querySelector' in document &&
		'addEventListener' in window &&
		'requestAnimationFrame' in window &&
		'closest' in window.Element.prototype;


	//
	// Default settings
	//

	var defaults = {
		// Selectors
		ignore: '[data-scroll-ignore]',
		header: null,
		
		// Speed & Easing
		speed: 500,
		offset: 0,
		easing: 'easeInOutCubic',
		customEasing: null,

		// Callback API
		before: function () {},
		after: function () {}
	};


	//
	// Utility Methods
	//

	/**
	 * Merge two or more objects. Returns a new object.
	 * @param {Object}   objects  The objects to merge together
	 * @returns {Object}          Merged values of defaults and options
	 */
	var extend = function () {

		// Variables
		var extended = {};
		var i = 0;
		var length = arguments.length;

		// Merge the object into the extended object
		var merge = function (obj) {
			for (var prop in obj) {
				if (obj.hasOwnProperty(prop)) {
					extended[prop] = obj[prop];
				}
			}
		};

		// Loop through each object and conduct a merge
		for ( ; i < length; i++ ) {
			var obj = arguments[i];
			merge(obj);
		}

		return extended;

	};

	/**
	 * Get the height of an element.
	 * @param  {Node} elem The element to get the height of
	 * @return {Number}    The element's height in pixels
	 */
	var getHeight = function (elem) {
		return parseInt(window.getComputedStyle(elem).height, 10);
	};

	/**
	 * Escape special characters for use with querySelector
	 * @param {String} id The anchor ID to escape
	 * @author Mathias Bynens
	 * @link https://github.com/mathiasbynens/CSS.escape
	 */
	var escapeCharacters = function (id) {

		// Remove leading hash
		if (id.charAt(0) === '#') {
			id = id.substr(1);
		}

		var string = String(id);
		var length = string.length;
		var index = -1;
		var codeUnit;
		var result = '';
		var firstCodeUnit = string.charCodeAt(0);
		while (++index < length) {
			codeUnit = string.charCodeAt(index);
			// Note: there’s no need to special-case astral symbols, surrogate
			// pairs, or lone surrogates.

			// If the character is NULL (U+0000), then throw an
			// `InvalidCharacterError` exception and terminate these steps.
			if (codeUnit === 0x0000) {
				throw new InvalidCharacterError(
					'Invalid character: the input contains U+0000.'
				);
			}

			if (
				// If the character is in the range [\1-\1F] (U+0001 to U+001F) or is
				// U+007F, […]
				(codeUnit >= 0x0001 && codeUnit <= 0x001F) || codeUnit == 0x007F ||
				// If the character is the first character and is in the range [0-9]
				// (U+0030 to U+0039), […]
				(index === 0 && codeUnit >= 0x0030 && codeUnit <= 0x0039) ||
				// If the character is the second character and is in the range [0-9]
				// (U+0030 to U+0039) and the first character is a `-` (U+002D), […]
				(
					index === 1 &&
					codeUnit >= 0x0030 && codeUnit <= 0x0039 &&
					firstCodeUnit === 0x002D
				)
			) {
				// http://dev.w3.org/csswg/cssom/#escape-a-character-as-code-point
				result += '\\' + codeUnit.toString(16) + ' ';
				continue;
			}

			// If the character is not handled by one of the above rules and is
			// greater than or equal to U+0080, is `-` (U+002D) or `_` (U+005F), or
			// is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to
			// U+005A), or [a-z] (U+0061 to U+007A), […]
			if (
				codeUnit >= 0x0080 ||
				codeUnit === 0x002D ||
				codeUnit === 0x005F ||
				codeUnit >= 0x0030 && codeUnit <= 0x0039 ||
				codeUnit >= 0x0041 && codeUnit <= 0x005A ||
				codeUnit >= 0x0061 && codeUnit <= 0x007A
			) {
				// the character itself
				result += string.charAt(index);
				continue;
			}

			// Otherwise, the escaped character.
			// http://dev.w3.org/csswg/cssom/#escape-a-character
			result += '\\' + string.charAt(index);

		}

		return '#' + result;

	};

	/**
	 * Calculate the easing pattern
	 * @link https://gist.github.com/gre/1650294
	 * @param {String} type Easing pattern
	 * @param {Number} time Time animation should take to complete
	 * @returns {Number}
	 */
	var easingPattern = function (settings, time) {
		var pattern;

		// Default Easing Patterns
		if (settings.easing === 'easeInQuad') pattern = time * time; // accelerating from zero velocity
		if (settings.easing === 'easeOutQuad') pattern = time * (2 - time); // decelerating to zero velocity
		if (settings.easing === 'easeInOutQuad') pattern = time < 0.5 ? 2 * time * time : -1 + (4 - 2 * time) * time; // acceleration until halfway, then deceleration
		if (settings.easing === 'easeInCubic') pattern = time * time * time; // accelerating from zero velocity
		if (settings.easing === 'easeOutCubic') pattern = (--time) * time * time + 1; // decelerating to zero velocity
		if (settings.easing === 'easeInOutCubic') pattern = time < 0.5 ? 4 * time * time * time : (time - 1) * (2 * time - 2) * (2 * time - 2) + 1; // acceleration until halfway, then deceleration
		if (settings.easing === 'easeInQuart') pattern = time * time * time * time; // accelerating from zero velocity
		if (settings.easing === 'easeOutQuart') pattern = 1 - (--time) * time * time * time; // decelerating to zero velocity
		if (settings.easing === 'easeInOutQuart') pattern = time < 0.5 ? 8 * time * time * time * time : 1 - 8 * (--time) * time * time * time; // acceleration until halfway, then deceleration
		if (settings.easing === 'easeInQuint') pattern = time * time * time * time * time; // accelerating from zero velocity
		if (settings.easing === 'easeOutQuint') pattern = 1 + (--time) * time * time * time * time; // decelerating to zero velocity
		if (settings.easing === 'easeInOutQuint') pattern = time < 0.5 ? 16 * time * time * time * time * time : 1 + 16 * (--time) * time * time * time * time; // acceleration until halfway, then deceleration

		// Custom Easing Patterns
		if (!!settings.customEasing) pattern = settings.customEasing(time);

		return pattern || time; // no easing, no acceleration
	};

	/**
	 * Determine the document's height
	 * @returns {Number}
	 */
	var getDocumentHeight = function () {
		return Math.max(
			document.body.scrollHeight, document.documentElement.scrollHeight,
			document.body.offsetHeight, document.documentElement.offsetHeight,
			document.body.clientHeight, document.documentElement.clientHeight
		);
	};

	/**
	 * Calculate how far to scroll
	 * @param {Element} anchor The anchor element to scroll to
	 * @param {Number} headerHeight Height of a fixed header, if any
	 * @param {Number} offset Number of pixels by which to offset scroll
	 * @returns {Number}
	 */
	var getEndLocation = function (anchor, headerHeight, offset) {
		var location = 0;
		if (anchor.offsetParent) {
			do {
				location += anchor.offsetTop;
				anchor = anchor.offsetParent;
			} while (anchor);
		}
		location = Math.max(location - headerHeight - offset, 0);
		return location;
	};

	/**
	 * Get the height of the fixed header
	 * @param  {Node}   header The header
	 * @return {Number}        The height of the header
	 */
	var getHeaderHeight = function (header) {
		return !header ? 0 : (getHeight(header) + header.offsetTop);
	};

	/**
	 * Bring the anchored element into focus
	 * @param {Node}     anchor      The anchor element
	 * @param {Number}   endLocation The end location to scroll to
	 * @param {Boolean}  isNum       If true, scroll is to a position rather than an element
	 */
	var adjustFocus = function (anchor, endLocation, isNum) {

		// Don't run if scrolling to a number on the page
		if (isNum) return;

		// Otherwise, bring anchor element into focus
		anchor.focus();
		if (document.activeElement.id !== anchor.id) {
			anchor.setAttribute('tabindex', '-1');
			anchor.focus();
			anchor.style.outline = 'none';
		}
		window.scrollTo(0 , endLocation);

	};

	/**
	 * Check to see if user prefers reduced motion
	 * @param  {Object} settings Script settings
	 */
	var reduceMotion = function (settings) {
		if ('matchMedia' in window && window.matchMedia('(prefers-reduced-motion)').matches) {
			return true;
		}
		return false;
	};


	//
	// SmoothScroll Constructor
	//

	var SmoothScroll = function (selector, options) {

		//
		// Variables
		//

		var smoothScroll = {}; // Object for public APIs
		var settings, anchor, toggle, fixedHeader, headerHeight, eventTimeout, animationInterval;


		//
		// Methods
		//

		/**
		 * Cancel a scroll-in-progress
		 */
		smoothScroll.cancelScroll = function () {
			// clearInterval(animationInterval);
			cancelAnimationFrame(animationInterval);
		};

		/**
		 * Start/stop the scrolling animation
		 * @param {Node|Number} anchor  The element or position to scroll to
		 * @param {Element}     toggle  The element that toggled the scroll event
		 * @param {Object}      options
		 */
		smoothScroll.animateScroll = function (anchor, toggle, options) {

			// Local settings
			var animateSettings = extend(settings || defaults, options || {}); // Merge user options with defaults

			// Selectors and variables
			var isNum = Object.prototype.toString.call(anchor) === '[object Number]' ? true : false;
			var anchorElem = isNum || !anchor.tagName ? null : anchor;
			if (!isNum && !anchorElem) return;
			var startLocation = window.pageYOffset; // Current location on the page
			if (animateSettings.header && !fixedHeader) {
				// Get the fixed header if not already set
				fixedHeader = document.querySelector( animateSettings.header );
			}
			if (!headerHeight) {
				// Get the height of a fixed header if one exists and not already set
				headerHeight = getHeaderHeight(fixedHeader);
			}
			var endLocation = isNum ? anchor : getEndLocation(anchorElem, headerHeight, parseInt((typeof animateSettings.offset === 'function' ? animateSettings.offset() : animateSettings.offset), 10)); // Location to scroll to
			var distance = endLocation - startLocation; // distance to travel
			var documentHeight = getDocumentHeight();
			var timeLapsed = 0;
			var start, percentage, position;

			/**
			 * Stop the scroll animation when it reaches its target (or the bottom/top of page)
			 * @param {Number} position Current position on the page
			 * @param {Number} endLocation Scroll to location
			 * @param {Number} animationInterval How much to scroll on this loop
			 */
			var stopAnimateScroll = function (position, endLocation) {

				// Get the current location
				var currentLocation = window.pageYOffset;

				// Check if the end location has been reached yet (or we've hit the end of the document)
				if ( position == endLocation || currentLocation == endLocation || ((startLocation < endLocation && window.innerHeight + currentLocation) >= documentHeight )) {

					// Clear the animation timer
					smoothScroll.cancelScroll();

					// Bring the anchored element into focus
					adjustFocus(anchor, endLocation, isNum);

					// Run callback after animation complete
					animateSettings.after(anchor, toggle);

					// Reset start
					start = null;

					return true;

				}
			};

			/**
			 * Loop scrolling animation
			 */
			var loopAnimateScroll = function (timestamp) {
				if (!start) { start = timestamp; }
				timeLapsed += timestamp - start;
				percentage = (timeLapsed / parseInt(animateSettings.speed, 10));
				percentage = (percentage > 1) ? 1 : percentage;
				position = startLocation + (distance * easingPattern(animateSettings, percentage));
				window.scrollTo(0, Math.floor(position));
				if (!stopAnimateScroll(position, endLocation)) {
					window.requestAnimationFrame(loopAnimateScroll);
					start = timestamp;
				}
			};

			/**
			 * Reset position to fix weird iOS bug
			 * @link https://github.com/cferdinandi/smooth-scroll/issues/45
			 */
			if (window.pageYOffset === 0) {
				window.scrollTo( 0, 0 );
			}

			// Run callback before animation starts
			animateSettings.before(anchor, toggle);

			// Start scrolling animation
			smoothScroll.cancelScroll();
			window.requestAnimationFrame(loopAnimateScroll);


		};

		/**
		 * Handle has change event
		 */
		var hashChangeHandler = function (event) {

			// Only run if there's an anchor element to scroll to
			if (!anchor) return;

			// Reset the anchor element's ID
			anchor.id = anchor.getAttribute('data-scroll-id');

			// Scroll to the anchored content
			smoothScroll.animateScroll(anchor, toggle);

			// Reset anchor and toggle
			anchor = null;
			toggle = null;

		};

		/**
		 * If smooth scroll element clicked, animate scroll
		 */
		var clickHandler = function (event) {

			// Don't run if the user prefers reduced motion
			if (reduceMotion(settings)) return;

			// Don't run if right-click or command/control + click
			if (event.button !== 0 || event.metaKey || event.ctrlKey) return;

			// Check if a smooth scroll link was clicked
			toggle = event.target.closest(selector);
			if (!toggle || toggle.tagName.toLowerCase() !== 'a' || event.target.closest(settings.ignore)) return;

			// Only run if link is an anchor and points to the current page
			if (toggle.hostname !== window.location.hostname || toggle.pathname !== window.location.pathname || !/#/.test(toggle.href)) return;

			// Get the sanitized hash
			var hash;
			try {
				hash = escapeCharacters(decodeURIComponent(toggle.hash));
			} catch(e) {
				hash = escapeCharacters(toggle.hash);
			}

			// If the hash is empty, scroll to the top of the page
			if (hash === '#') {

				// Prevent default link behavior
				event.preventDefault();

				// Set the anchored element
				anchor = document.body;

				// Save or create the ID as a data attribute and remove it (prevents scroll jump)
				var id = anchor.id ? anchor.id : 'smooth-scroll-top';
				anchor.setAttribute('data-scroll-id', id);
				anchor.id = '';

				// If no hash change event will happen, fire manually
				// Otherwise, update the hash
				if (window.location.hash.substring(1) === id) {
					hashChangeHandler();
				} else {
					window.location.hash = id;
				}

				return;

			}

			// Get the anchored element
			anchor = document.querySelector(hash);

			// If anchored element exists, save the ID as a data attribute and remove it (prevents scroll jump)
			if (!anchor) return;
			anchor.setAttribute('data-scroll-id', anchor.id);
			anchor.id = '';

			// If no hash change event will happen, fire manually
			if (toggle.hash === window.location.hash) {
				event.preventDefault();
				hashChangeHandler();
			}

		};

		/**
		 * On window scroll and resize, only run events at a rate of 15fps for better performance
		 */
		var resizeThrottler = function (event) {
			if (!eventTimeout) {
				eventTimeout = setTimeout(function() {
					eventTimeout = null; // Reset timeout
					headerHeight = getHeaderHeight(fixedHeader); // Get the height of a fixed header if one exists
				}, 66);
			}
		};

		/**
		 * Destroy the current initialization.
		 */
		smoothScroll.destroy = function () {

			// If plugin isn't already initialized, stop
			if (!settings) return;

			// Remove event listeners
			document.removeEventListener('click', clickHandler, false);
			window.removeEventListener('resize', resizeThrottler, false);

			// Cancel any scrolls-in-progress
			smoothScroll.cancelScroll();

			// Reset variables
			settings = null;
			anchor = null;
			toggle = null;
			fixedHeader = null;
			headerHeight = null;
			eventTimeout = null;
			animationInterval = null;
		};

		/**
		 * Initialize Smooth Scroll
		 * @param {Object} options User settings
		 */
		smoothScroll.init = function (options) {

			// feature test
			if (!supports) return;

			// Destroy any existing initializations
			smoothScroll.destroy();

			// Selectors and variables
			settings = extend(defaults, options || {}); // Merge user options with defaults
			fixedHeader = settings.header ? document.querySelector(settings.header) : null; // Get the fixed header
			headerHeight = getHeaderHeight(fixedHeader);

			// When a toggle is clicked, run the click handler
			document.addEventListener('click', clickHandler, false);

			// Listen for hash changes
			window.addEventListener('hashchange', hashChangeHandler, false);

			// If window is resized and there's a fixed header, recalculate its size
			if (fixedHeader) {
				window.addEventListener('resize', resizeThrottler, false);
			}

		};


		//
		// Initialize plugin
		//

		smoothScroll.init(options);


		//
		// Public APIs
		//

		return smoothScroll;

	};

	return SmoothScroll;

});