docs: add google analytics tracking

docs/conf_common.py

@@ -59,6 +59,7 @@ extensions = ['breathe',
               'extensions.html_redirects',
               'extensions.toctree_filter',
               'extensions.list_filter',
+              'extensions.google_analytics',
 
               # Note: order is important here, events must
               # be registered by one extension before they can be
@@ -361,6 +362,8 @@ html_static_path = ['../_static']
 # Output file base name for HTML help builder.
 htmlhelp_basename = 'ReadtheDocsTemplatedoc'
 
+google_analytics_id = os.environ['CI_GOOGLE_ANALYTICS_ID']
+
 # -- Options for LaTeX output ---------------------------------------------
 
 latex_template_dir = os.path.join(config_dir, 'latex_templates')

docs/extensions/google_analytics.py

@@ -0,0 +1,30 @@
+# Embeds a google analytics tracking tag in every HTML page
+def setup(app):
+    app.add_config_value('google_analytics_id', None, 'html')
+    app.connect('html-page-context', google_analytics_embed)
+
+    return {'parallel_read_safe': True, 'parallel_write_safe': True, 'version': '0.1'}
+
+
+def google_analytics_embed(app, pagename, templatename, context, doctree):
+
+    ga_id = app.config.google_analytics_id
+    if not ga_id:
+        return
+
+    metatags = context.get('metatags', '')
+
+    google_analytics_snippet = """
+        <!-- Global site tag (gtag.js) - Google Analytics -->
+        <script async src="https://www.googletagmanager.com/gtag/js?id={}"></script>
+        <script>
+            window.dataLayer = window.dataLayer || [];
+            function gtag(){{dataLayer.push(arguments);}}
+            gtag('js', new Date());
+
+            gtag('config', '{}');
+        </script>""".format(ga_id, ga_id)
+
+    # Prepend the google analytics to the HTML metatags (which will be passed to the sphinx templating engine)
+    metatags = google_analytics_snippet + metatags
+    context['metatags'] = metatags