Migrate to Google Analytics 4, GA4 as UA is deprecated

Main repo that this is forked from does not appear to be
maintained. Referenced mmistakes/so-simple-theme#429

Author: leewc

_config.yml

@@ -30,7 +30,7 @@ google_fonts:
     weights: "400,400i,700,700i"
   - name: "Lora"
     weights: "400,400i,700,700i"
-google_analytics: UA-64050901-1
+google_analytics: G-R1L5NXLCYC
 disqus:
   shortname: leewc
 twitter:

_includes/google-analytics-custom.html

@@ -0,0 +1,24 @@
+{% comment %} 
+  Old style Google analytics uses codes of the form UA-XXXXXXXX. The new Google Analytics 4 uses codes of the form G-XXXXXXX. Each has different javascript.
+{% endcomment %}
+
+{%- if site.google_analytics contains 'UA-' -%}
+  <script>
+  if(!(window.doNotTrack === "1" || navigator.doNotTrack === "1" || navigator.doNotTrack === "yes" || navigator.msDoNotTrack === "1")) {
+    (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+    })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+    ga('create', '{{ site.google_analytics }}', 'auto');
+    ga('send', 'pageview');
+  }
+  </script>
+{%- else %}
+  <script async src="https://www.googletagmanager.com/gtag/js?id={{ site.google_analytics }}"></script>
+  <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+    gtag('config', '{{ site.google_analytics }}');
+  </script>
+{% endif %}

_includes/scripts.html

@@ -0,0 +1,54 @@
+{%- if site.footer_scripts -%}
+  {%- for script in site.footer_scripts -%}
+    {%- if script contains "://" -%}
+      {%- capture script_path %}{{ script }}{% endcapture -%}
+    {%- else -%}
+      {%- capture script_path %}{{ script | absolute_url }}{% endcapture -%}
+    {%- endif -%}
+    <script src="{{ script_path }}"></script>
+  {%- endfor -%}
+{%- else -%}
+  <script src="https://code.jquery.com/jquery-3.3.1.min.js" integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
+  <script src="{{ '/assets/js/main.min.js' | relative_url }}"></script>
+  <script src="https://use.fontawesome.com/releases/v5.0.12/js/all.js"></script>
+{%- endif -%}
+
+{%- if jekyll.environment == 'production' and site.google_analytics -%}
+    <!-- leewc: Override google-analytics from main theme given main theme is not maintained -->
+    {% include google-analytics-custom.html %}
+{%- endif %}
+
+{% if site.mathjax == true or site.mathjax.enable == true %}
+<!-- MathJax -->
+{% capture mathjaxjs %}https://cdn.jsdelivr.net/npm/mathjax@3/es5/{{ site.mathjax.combo | default: "tex-svg" }}.js{% endcapture %}
+<script>
+// http://docs.mathjax.org/en/latest/upgrading/v2.html
+MathJax = {
+  tex: {
+      tags: "{{ site.mathjax.tags | default: 'ams' }}"    // eq numbering options: none, ams, all
+  },
+  options: {
+    renderActions: {
+      // for mathjax 3, handle <script "math/tex"> blocks inserted by kramdown
+      find: [10, function (doc) {
+        for (const node of document.querySelectorAll('script[type^="math/tex"]')) {
+          const display = !!node.type.match(/; *mode=display/);
+          const math = new doc.options.MathItem(node.textContent, doc.inputJax[0], display);
+          const text = document.createTextNode('');
+          node.parentNode.replaceChild(text, node);
+          math.start = {node: text, delim: '', n: 0};
+          math.end = {node: text, delim: '', n: 0};
+          doc.math.push(math);
+        }
+      }, '']
+    }
+  }
+}
+</script>
+
+<script type="text/javascript" id="MathJax-script" async src="{{ mathjaxjs }}"></script>
+{% endif %}
+
+{%- if page.layout == "search" -%}
+  {% include lunr-search-scripts.html %}
+{%- endif -%}