(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';

	//
	// Default settings
	//

	var defaults = {

		// Selectors
		ignore: '[data-scroll-ignore]',
		header: null,
		topOnEmptyHash: true,

		// Speed & Duration
		speed: 500,
		speedAsDuration: false,
		durationMax: null,
		durationMin: null,
		clip: true,
		offset: 0,

		// Easing
		easing: 'easeInOutCubic',
		customEasing: null,

		// History
		updateURL: true,
		popstate: true,

		// Custom Events
		emitEvents: true

	};


	//
	// Utility Methods
	//

	/**
	 * Check if browser supports required methods
	 * @return {Boolean} Returns true if all required methods are supported
	 */
	var supports = function () {
		return (
			'querySelector' in document &&
			'addEventListener' in window &&
			'requestAnimationFrame' in window &&
			'closest' in window.Element.prototype
		);
	};

	/**
	 * Merge two or more objects together.
	 * @param   {Object}   objects  The objects to merge together
	 * @returns {Object}            Merged values of defaults and options
	 */
	var extend = function () {
		var merged = {};
		Array.prototype.forEach.call(arguments, function (obj) {
			for (var key in obj) {
				if (!obj.hasOwnProperty(key)) return;
				merged[key] = obj[key];
			}
		});
		return merged;
	};

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

	/**
	 * 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
	 * @author Mathias Bynens
	 * @link https://github.com/mathiasbynens/CSS.escape
	 * @param {String} id The anchor ID to 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 sanitized hash
		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
	 * Clip support added by robjtede - https://github.com/cferdinandi/smooth-scroll/issues/405
	 * @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
	 * @param {Boolean} clip         If true, adjust scroll distance to prevent abrupt stops near the bottom of the page
	 * @returns {Number}
	 */
	var getEndLocation = function (anchor, headerHeight, offset, clip) {
		var location = 0;
		if (anchor.offsetParent) {
			do {
				location += anchor.offsetTop;
				anchor = anchor.offsetParent;
			} while (anchor);
		}
		location = Math.max(location - headerHeight - offset, 0);
		if (clip) {
			location = Math.min(location, getDocumentHeight() - window.innerHeight);
		}
 		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);
	};

	/**
	 * Calculate the speed to use for the animation
	 * @param  {Number} distance The distance to travel
	 * @param  {Object} settings The plugin settings
	 * @return {Number}          How fast to animate
	 */
	var getSpeed = function (distance, settings) {
		var speed = settings.speedAsDuration ? settings.speed : Math.abs(distance / 1000 * settings.speed);
		if (settings.durationMax && speed > settings.durationMax) return settings.durationMax;
		if (settings.durationMin && speed < settings.durationMin) return settings.durationMin;
		return parseInt(speed, 10);
	};

	var setHistory = function (options) {

		// Make sure this should run
		if (!history.replaceState || !options.updateURL || history.state) return;

		// Get the hash to use
		var hash = window.location.hash;
		hash = hash ? hash : '';

		// Set a default history
		history.replaceState(
			{
				smoothScroll: JSON.stringify(options),
				anchor: hash ? hash : window.pageYOffset
			},
			document.title,
			hash ? hash : window.location.href
		);

	};

	/**
	 * Update the URL
	 * @param  {Node}    anchor  The anchor that was scrolled to
	 * @param  {Boolean} isNum   If true, anchor is a number
	 * @param  {Object}  options Settings for Smooth Scroll
	 */
	var updateURL = function (anchor, isNum, options) {

		// Bail if the anchor is a number
		if (isNum) return;

		// Verify that pushState is supported and the updateURL option is enabled
		if (!history.pushState || !options.updateURL) return;

		// Update URL
		history.pushState(
			{
				smoothScroll: JSON.stringify(options),
				anchor: anchor.id
			},
			document.title,
			anchor === document.documentElement ? '#top' : '#' + anchor.id
		);

	};

	/**
	 * 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) {

		// Is scrolling to top of page, blur
		if (anchor === 0) {
			document.body.focus();
		}

		// 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 !== anchor) {
			anchor.setAttribute('tabindex', '-1');
			anchor.focus();
			anchor.style.outline = 'none';
		}
		window.scrollTo(0 , endLocation);

	};

	/**
	 * Emit a custom event
	 * @param  {String} type    The event type
	 * @param  {Object} options The settings object
	 * @param  {Node}   anchor  The anchor element
	 * @param  {Node}   toggle  The toggle element
	 */
	var emitEvent = function (type, options, anchor, toggle) {
		if (!options.emitEvents || typeof window.CustomEvent !== 'function') return;
		var event = new CustomEvent(type, {
			bubbles: true,
			detail: {
				anchor: anchor,
				toggle: toggle
			}
		});
		document.dispatchEvent(event);
	};


	//
	// SmoothScroll Constructor
	//

	var SmoothScroll = function (selector, options) {

		//
		// Variables
		//

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


		//
		// Methods
		//

		/**
		 * Cancel a scroll-in-progress
		 */
		smoothScroll.cancelScroll = function (noEvent) {
			cancelAnimationFrame(animationInterval);
			animationInterval = null;
			if (noEvent) return;
			emitEvent('scrollCancel', settings);
		};

		/**
		 * 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) {

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

			// Local settings
			var _settings = 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 (_settings.header && !fixedHeader) {
				// Get the fixed header if not already set
				fixedHeader = document.querySelector(_settings.header);
			}
			var headerHeight = getHeaderHeight(fixedHeader);
			var endLocation = isNum ? anchor : getEndLocation(anchorElem, headerHeight, parseInt((typeof _settings.offset === 'function' ? _settings.offset(anchor, toggle) : _settings.offset), 10), _settings.clip); // Location to scroll to
			var distance = endLocation - startLocation; // distance to travel
			var documentHeight = getDocumentHeight();
			var timeLapsed = 0;
			var speed = getSpeed(distance, _settings);
			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(true);

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

					// Emit a custom event
					emitEvent('scrollStop', _settings, anchor, toggle);

					// Reset start
					start = null;
					animationInterval = null;

					return true;

				}
			};

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

			// Update the URL
			updateURL(anchor, isNum, _settings);

			// If the user prefers reduced motion, jump to location
			if (reduceMotion()) {
				adjustFocus(anchor, Math.floor(endLocation), false);
				return;
			}

			// Emit a custom event
			emitEvent('scrollStart', _settings, anchor, toggle);

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

		};

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

			// Don't run if event was canceled but still bubbled up
			// By @mgreter - https://github.com/cferdinandi/smooth-scroll/pull/462/
			if (event.defaultPrevented) return;

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

			// Check if event.target has closest() method
			// By @totegi - https://github.com/cferdinandi/smooth-scroll/pull/401/
			if (!('closest' in event.target)) 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 an escaped version of the hash
			var hash;
			try {
				hash = escapeCharacters(decodeURIComponent(toggle.hash));
			} catch(e) {
				hash = escapeCharacters(toggle.hash);
			}

			// Get the anchored element
			var anchor;
			if (hash === '#') {
				if (!settings.topOnEmptyHash) return;
				anchor = document.documentElement;
			} else {
				anchor = document.querySelector(hash);
			}
			anchor = !anchor && hash === '#top' ? document.documentElement : anchor;

			// If anchored element exists, scroll to it
			if (!anchor) return;
			event.preventDefault();
			setHistory(settings);
			smoothScroll.animateScroll(anchor, toggle);

		};

		/**
		 * Animate scroll on popstate events
		 */
		var popstateHandler = function (event) {

			// Stop if history.state doesn't exist (ex. if clicking on a broken anchor link).
			// fixes `Cannot read property 'smoothScroll' of null` error getting thrown.
			if (history.state === null) return;

			// Only run if state is a popstate record for this instantiation
			if (!history.state.smoothScroll || history.state.smoothScroll !== JSON.stringify(settings)) return;

			// Only run if state includes an anchor

			// if (!history.state.anchor && history.state.anchor !== 0) return;

			// Get the anchor
			var anchor = history.state.anchor;
			if (typeof anchor === 'string' && anchor) {
				anchor = document.querySelector(escapeCharacters(history.state.anchor));
				if (!anchor) return;
			}

			// Animate scroll to anchor link
			smoothScroll.animateScroll(anchor, null, {updateURL: false});

		};

		/**
		 * 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('popstate', popstateHandler, false);

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

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

		};

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

			// feature test
			if (!supports()) throw 'Smooth Scroll: This browser does not support the required JavaScript methods and browser APIs.';

			// 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

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

			// If updateURL and popState are enabled, listen for pop events
			if (settings.updateURL && settings.popstate) {
				window.addEventListener('popstate', popstateHandler, false);
			}

		};


		//
		// Initialize plugin
		//

		init();


		//
		// Public APIs
		//

		return smoothScroll;

	};

	return SmoothScroll;

});
