[Statsig] Sample noisy events (#4288)

* Sample state:background and state:foreground

* Sample feed events

* Add DEV protection against forgetting to add events to the list

src/lib/statsig/events.ts

@@ -20,10 +20,10 @@ export type LogEvents = {
     context: 'StartOnboarding' | 'AfterOnboarding' | 'Login'
     status: 'granted' | 'denied' | 'undetermined'
   }
-  'state:background': {
+  'state:background:sampled': {
     secondsActive: number
   }
-  'state:foreground': {}
+  'state:foreground:sampled': {}
   'router:navigate:sampled': {}
 
   // Screen events
@@ -57,18 +57,18 @@ export type LogEvents = {
   'onboarding:finished:avatarResult': {
     avatarResult: 'default' | 'created' | 'uploaded'
   }
-  'home:feedDisplayed': {
+  'home:feedDisplayed:sampled': {
     feedUrl: string
     feedType: string
     index: number
     reason: 'focus' | 'tabbar-click' | 'pager-swipe' | 'desktop-sidebar-click'
   }
-  'feed:endReached': {
+  'feed:endReached:sampled': {
     feedUrl: string
     feedType: string
     itemCount: number
   }
-  'feed:refresh': {
+  'feed:refresh:sampled': {
     feedUrl: string
     feedType: string
     reason: 'pull-to-refresh' | 'soft-reset' | 'load-latest'

src/lib/statsig/statsig.tsx

@@ -87,7 +87,14 @@ export function toClout(n: number | null | undefined): number | undefined {
   }
 }
 
-const DOWNSAMPLED_EVENTS = new Set(['router:navigate:sampled'])
+const DOWNSAMPLED_EVENTS: Set<keyof LogEvents> = new Set([
+  'router:navigate:sampled',
+  'state:background:sampled',
+  'state:foreground:sampled',
+  'home:feedDisplayed:sampled',
+  'feed:endReached:sampled',
+  'feed:refresh:sampled',
+])
 const isDownsampledSession = Math.random() < 0.9 // 90% likely
 
 export function logEvent<E extends keyof LogEvents>(
@@ -98,6 +105,13 @@ export function logEvent<E extends keyof LogEvents>(
     if (isDownsampledSession && DOWNSAMPLED_EVENTS.has(eventName)) {
       return
     }
+    if (process.env.NODE_ENV === 'development') {
+      if (eventName.endsWith(':sampled')) {
+        logger.error(
+          'Did you forget to add ' + eventName + ' to DOWNSAMPLED_EVENTS?',
+        )
+      }
+    }
     const fullMetadata = {
       ...rawMetadata,
     } as Record<string, string> // Statsig typings are unnecessarily strict here.
@@ -199,14 +213,14 @@ AppState.addEventListener('change', (state: AppStateStatus) => {
   lastState = state
   if (state === 'active') {
     lastActive = performance.now()
-    logEvent('state:foreground', {})
+    logEvent('state:foreground:sampled', {})
   } else {
     let secondsActive = 0
     if (lastActive != null) {
       secondsActive = Math.round((performance.now() - lastActive) / 1e3)
     }
     lastActive = null
-    logEvent('state:background', {
+    logEvent('state:background:sampled', {
       secondsActive,
     })
   }