♻️(frontend) encapsulate PostHog logic in dedicated functions

Decouple the code from the PostHog dependency by wrapping it in a custom hook
and several utility functions. This enhances code maintainability and separation
of concerns.

src/frontend/src/App.tsx

@@ -1,11 +1,11 @@
 import '@livekit/components-styles'
 import '@/styles/index.css'
-import { Suspense, useEffect } from 'react'
+import { Suspense } from 'react'
 import { ReactQueryDevtools } from '@tanstack/react-query-devtools'
 import { QueryClientProvider } from '@tanstack/react-query'
 import { useTranslation } from 'react-i18next'
 import { useLang } from 'hoofd'
-import { Switch, Route, useLocation } from 'wouter'
+import { Switch, Route } from 'wouter'
 import { I18nProvider } from 'react-aria-components'
 import { Layout } from './layout/Layout'
 import { NotFoundScreen } from './components/NotFoundScreen'
@@ -13,28 +13,16 @@ import { routes } from './routes'
 import './i18n/init'
 import { silenceLiveKitLogs } from '@/utils/livekit.ts'
 import { queryClient } from '@/api/queryClient'
-import posthog from 'posthog-js'
+import { useAnalytics } from '@/features/analytics/hooks/useAnalytics'
 
 function App() {
   const { i18n } = useTranslation()
-  const [location] = useLocation()
   useLang(i18n.language)
 
   const isProduction = import.meta.env.PROD
   silenceLiveKitLogs(isProduction)
 
-  // We're on a free tier, so we need to limit the number of events we send to PostHog.
-  // Be frugal with event tracking, even though we could filter them out later if necessary.
-  if (isProduction) {
-    posthog.init('phc_RPYko028Oqtj0c9exLIWwrlrjLxSdxT0ntW0Lam4iom', {
-      api_host: 'https://eu.i.posthog.com',
-      person_profiles: 'always',
-    })
-  }
-
-  useEffect(() => {
-    posthog.capture('$pageview')
-  }, [location])
+  useAnalytics()
 
   return (
     <QueryClientProvider client={queryClient}>

src/frontend/src/features/analytics/hooks/useAnalytics.tsx

@@ -0,0 +1,42 @@
+import { useEffect } from 'react'
+import { useLocation } from 'wouter'
+import posthog from 'posthog-js'
+import { ApiUser } from '@/features/auth/api/ApiUser'
+
+const ANALYTICS_ID = 'phc_RPYko028Oqtj0c9exLIWwrlrjLxSdxT0ntW0Lam4iom'
+const ANALYTICS_HOST = 'https://eu.i.posthog.com'
+
+export const startAnalyticsSession = (data: ApiUser) => {
+  if (posthog._isIdentified()) return
+  const { id, email } = data
+  posthog.identify(id, { email })
+}
+
+export const terminateAnalyticsSession = () => {
+  if (!posthog._isIdentified()) return
+  posthog.reset()
+}
+
+export const useAnalytics = () => {
+  const [location] = useLocation()
+
+  const isProduction = import.meta.env.PROD
+
+  useEffect(() => {
+    // We're on a free tier, so we need to limit the number of events we send to PostHog.
+    // Be frugal with event tracking, even though we could filter them out later if necessary.
+    if (!isProduction) return
+    if (posthog.__loaded) return
+    posthog.init(ANALYTICS_ID, {
+      api_host: ANALYTICS_HOST,
+      person_profiles: 'always',
+    })
+  }, [isProduction])
+
+  // From PostHog tutorial on PageView tracking in a Single Page Application (SPA) context.
+  useEffect(() => {
+    posthog.capture('$pageview')
+  }, [location])
+
+  return null
+}

src/frontend/src/features/auth/api/useUser.tsx

@@ -3,10 +3,10 @@ import { keys } from '@/api/queryKeys'
 import { fetchUser } from './fetchUser'
 import { type ApiUser } from './ApiUser'
 import { useEffect } from 'react'
-import posthog from 'posthog-js'
+import { startAnalyticsSession } from '@/features/analytics/hooks/useAnalytics'
 
 /**
- * returns info about currently logged in user
+ * returns info about currently logged-in user
  *
  * `isLoggedIn` is undefined while query is loading and true/false when it's done
  */
@@ -18,8 +18,8 @@ export const useUser = () => {
   })
 
   useEffect(() => {
-    if (query.data && query.data.id && !posthog._isIdentified()) {
-      posthog.identify(query.data.id, { email: query.data.email })
+    if (query?.data) {
+      startAnalyticsSession(query.data)
     }
   }, [query.data])
 

src/frontend/src/layout/Header.tsx

@@ -9,8 +9,8 @@ import { useMatchesRoute } from '@/navigation/useMatchesRoute'
 import { Feedback } from '@/components/Feedback'
 import { Menu } from '@/primitives/Menu'
 import { MenuList } from '@/primitives/MenuList'
-import posthog from 'posthog-js'
 import { ProConnectButton } from '@/components/ProConnectButton'
+import { terminateAnalyticsSession } from '@/features/analytics/hooks/useAnalytics'
 
 export const Header = () => {
   const { t } = useTranslation()
@@ -81,7 +81,7 @@ export const Header = () => {
                   items={[{ value: 'logout', label: t('logout') }]}
                   onAction={(value) => {
                     if (value === 'logout') {
-                      posthog.reset()
+                      terminateAnalyticsSession()
                       window.location.href = logoutUrl()
                     }
                   }}