var engage = function() {
	var helper = {
		track_referrer: true,
		domain: function() {
			return window.location.hostname;
		},
		referrer: function() {
			var referrer = '';
			if (!helper.track_referrer) {
				return referrer;
			}

			// only track referrer once
			helper.track_referrer = false;
			try {
				referrer = top.document.referrer;
			} catch (e1) {
				try {
					referrer = parent.document.referrer;
				} catch (e2) {
					referrer = '';
				}
			}

			if (referrer == '') {
				referrer = document.referrer;
			}

			return referrer;
		},
		agent: function() {
			return navigator.userAgent;
		},
		resource: function() {
			return document.location.href;
		},
		timestamp: function() {
			return Date.now();
		},
		requestId: function(url, timestamp) {
			var hashString = function (s) {
				if (s && s.length) {
					var h = 0;

					for (var i = 0; i < s.length; i++) {
						h += s.charCodeAt(i);
						h += (h << 10);
						h ^= (h >> 6);
						h = h & h;
					}

					h += (h << 3);
					h ^= (h >> 11);
					h += (h << 15);
					h = h & h;

					return h;
				}

				console.log({ warning: 'Hashing null or empty string' });
				return 0;
			}

			return hashString(url + ';' + timestamp);
		},
		title: function() {
			return document.title;
		},
		screenWidth: function() {
			try {
				return screen.width;
			} catch (e) {
				return 0;
			}
		},
		browserDimensions: function() {
			var width = 0,
				height = 0;
			try {
				if (typeof (window.innerWidth) == 'number') {
					width = window.innerWidth;
					height = window.innerHeight;
				} else if (document.documentElement && document.documentElement.clientWidth) {
					width = document.documentElement.clientWidth;
					height = document.documentElement.clientHeight;
				} else if (document.body && document.body.clientWidth) {
					width = document.body.clientWidth;
					height = document.body.clientHeight;
				}
			} catch (e) {
			}
			return {
				width: width,
				height: height
			}
		},
		browserWidth: function() {
			return helper.browserDimensions().width;
		},
		browserHeight: function() {
			return helper.browserDimensions().height;
		},
		eventData: function () {
			var timestamp = helper.timestamp();
			var url = helper.resource();
			var requestId = helper.requestId(url, timestamp);
			return {
				requestId: requestId,
				url: url,
				referrer: helper.referrer(),
				title: helper.title(),
				userAgent: helper.agent(),
				screenWidth: helper.screenWidth(),
				browserWidth: helper.browserWidth(),
				browserHeight: helper.browserHeight(),
				timestamp: timestamp,
			};
		},
		getCookie: function(cookieName) {
			var x = cookieName + "=",
				values = document.cookie.split(';');
			for (var index = 0; index < values.length; index++) {
				var cookie = values[index];
				while (cookie.charAt(0) == ' ') {
					cookie = cookie.substring(1, cookie.length);
				}
				if (cookie.indexOf(x) == 0) {
					return unescape(cookie.substring(x.length, cookie.length));
				}
			}
			return null;
		},
		setCookie: function (cookieName, data) {
			document.cookie = cookieName + '=' + escape(data);
		},
		getFromStorage: function (key) {
			if (window.localStorage) {
				var item = window.localStorage.getItem(key);
				if (item) {
					return JSON.parse(item);
				}
			} else {
				return JSON.parse(helper.getCookie(key));
			}

			return null;
		},
		setToStorage: function (key, data) {
			if (window.localStorage) {
				if (data) {
					window.localStorage.setItem(key, JSON.stringify(data));
				} else {
					window.localStorage.removeItem(key);
				}
			} else {
				helper.setCookie(key, JSON.stringify(data));
			}

			return null;
		},
		createCORSRequest: function (method, url, withCredentials) {
			var xhr = new XMLHttpRequest();
			if ("withCredentials" in xhr) {
				// Check if the XMLHttpRequest object has a "withCredentials" property.
				// "withCredentials" only exists on XMLHTTPRequest2 objects.
				xhr.open(method, url, true);
				xhr.withCredentials = withCredentials;
			} else if (typeof XDomainRequest != "undefined") {
				// Otherwise, check if XDomainRequest.
				// XDomainRequest only exists in IE, and is IE's way of making CORS requests.
				xhr = new XDomainRequest();
				xhr.open(method, url);

			} else {
				// Otherwise, CORS is not supported by the browser.
				xhr = null;
			}
			return xhr;
		},
		getNewSasToken: function (method, url, data, callback) {
			var xhr = helper.createCORSRequest(method, url, true);
			if (xhr) {
				xhr.onreadystatechange = function() {
					if (xhr.readyState === 4) {
						if (xhr.status === 200) {
							callback(JSON.parse(xhr.responseText));
						} else {
							console.log({ sasStatus: xhr });
						}
					}
				}

				if (method === "POST") {
					xhr.setRequestHeader("Content-type", "application/json");
					if (data) {
						xhr.send(JSON.stringify(data));
					} else {
						xhr.send();
					}
				} else {
					xhr.send();
				}
			}
		}
	};

	var tracker = function() {
		return {
			init: function(renewUrl, resetSas, callback) {
				var sas = helper.getFromStorage("engage:sas");
				if (sas && resetSas !== "true" && sas.tokenExpires > Date.now()) {
					callback(sas);
				} else {
					helper.getNewSasToken("POST", renewUrl, null, function (token) {
						helper.setToStorage("engage:sas", token);
						callback(token);
					});
				}
			},

			send: function (sas) {
				var xhr = helper.createCORSRequest("POST", sas.url, false);
				if (xhr) {
					xhr.setRequestHeader("Content-Type", "application/atom+xml;type=entry;charset=utf-8");
					if (sas.token) {
						xhr.setRequestHeader("Authorization", sas.token);
					}

					var eventData = helper.eventData();
					eventData.ipAddress = sas.ipAddress;

					xhr.onreadystatechange = function() {
						if (this.readyState === 4) {
							/* success */
						}
					};

					xhr.send(JSON.stringify(eventData));
				}
			}
		}
	}

	return {
		tracker: tracker()
	}
}();

engage.tracker.init("https://wt.engage.ubiquity.co.nz/device/renew/83v5t6xp1c01p5g_rwdlvb1grvcx6l6hbt3j28mymk7j6wc_8d20", "false", function(sasToken) {
	engage.tracker.send(sasToken);
});