respect dnt settings and track outbound clicks

src/layouts/partials/analytics.html

@@ -1,10 +1,70 @@
 <!-- Google Analytics -->
-<script async src="https://www.googletagmanager.com/gtag/js?id=UA-96910779-8"></script>
 <script>
-  if (location.hostname !== 'localhost') {
-    window.dataLayer = window.dataLayer || [];
-    function gtag(){dataLayer.push(arguments);}
-    gtag('js', new Date());
-    gtag('config', 'UA-96910779-8');
+  // https://github.com/schalkneethling/dnt-helper/blob/master/js/dnt-helper.js
+  function _dntEnabled(dnt, userAgent) {
+    "use strict";
+    var dntStatus =
+      dnt ||
+      navigator.doNotTrack ||
+      window.doNotTrack ||
+      navigator.msDoNotTrack;
+    var ua = userAgent || navigator.userAgent;
+    var anomalousWinVersions = [
+      "Windows NT 6.1",
+      "Windows NT 6.2",
+      "Windows NT 6.3"
+    ];
+    var fxMatch = ua.match(/Firefox\/(\d+)/);
+    var ieRegEx = /MSIE|Trident/i;
+    var isIE = ieRegEx.test(ua);
+    var platform = ua.match(/Windows.+?(?=;)/g);
+    if (isIE && typeof Array.prototype.indexOf !== "function") {
+      return false;
+    } else if (fxMatch && parseInt(fxMatch[1], 10) < 32) {
+      dntStatus = "Unspecified";
+    } else if (
+      isIE &&
+      platform &&
+      anomalousWinVersions.indexOf(platform.toString()) !== -1
+    ) {
+      dntStatus = "Unspecified";
+    } else {
+      dntStatus =
+        { "0": "Disabled", "1": "Enabled" }[dntStatus] || "Unspecified";
     }
+    return dntStatus === "Enabled";
+  }
+
+  (function() {
+    if (!_dntEnabled() && location.hostname !== "localhost") {
+      !(function(n, o, d, e, j, s) {
+        n.GoogleAnalyticsObject = d;
+        n[d] ||
+          (n[d] = function() {
+            (n[d].q = n[d].q || []).push(arguments);
+          });
+        n[d].l = +new Date();
+        j = o.createElement(e);
+        s = o.getElementsByTagName(e)[0];
+        j.async = 1;
+        j.src = "//www.google-analytics.com/analytics.js";
+        s.parentNode.insertBefore(j, s);
+      })(window, document, "ga", "script");
+      if (!ga) return;
+      ga("create", "UA-96910779-8", "auto");
+      ga("send", "pageview");
+
+      // track outbound project clicks
+      document.addEventListener(
+        "click",
+        function(e) {
+          var href = e.target.closest("a") && e.target.closest("a").href;
+          if (href && href.indexOf("http") > -1) {
+            ga("send", "event", "outbound", "click", href);
+          }
+        },
+        false
+      );
+    }
+  })();
 </script>