add opt out for mixpanel tracking

app/javascript/packs/application.js

@@ -43,4 +43,4 @@ export { default as Shortcuts } from '../src/javascripts/shortcuts.js';
 export { default as Upload } from '../src/javascripts/uploads.js';
 export { default as Utility } from '../src/javascripts/utility.js';
 export { default as Ugoira } from '../src/javascripts/ugoira.js';
-
+export { mixpanelInit, mixpanelEvent } from '../src/javascripts/mixpanel.js';

app/javascript/src/javascripts/mixpanel.js

@@ -0,0 +1,27 @@
+const mixpanelInit = (user_id, session_id, opt_out, user_data) => {
+  if (typeof window.mixpanel !== "object") {
+    return;
+  }
+
+  if (user_id) {
+    window.mixpanel.identify(user_id);
+
+    if (opt_out) {
+      window.mixpanel.opt_out_tracking();
+    } else {
+      window.mixpanel.people.set(user_data);
+    }
+  } else if (session_id) {
+    window.mixpanel.identify("anon:" + session_id);
+  }
+}
+
+const mixpanelEvent = (title, props) => {
+  if (typeof window.mixpanel !== "object") {
+    return;
+  }
+
+  window.mixpanel.track(title, props);
+}
+
+export { mixpanelInit, mixpanelEvent };