♻️ Add abstractions for tracking server-side events (#1143)

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

packages/backend/package.json

@@ -12,7 +12,6 @@
     "@rallly/database": "*",
     "@rallly/emails": "*",
     "@rallly/utils": "*",
-    "@vercel/functions": "^1.0.2",
     "@trpc/server": "^10.13.0",
     "iron-session": "^6.3.1",
     "spacetime": "^7.4.7",

packages/backend/trpc/context.ts

@@ -1,6 +1,7 @@
 import { EmailClient } from "@rallly/emails";
 import { inferAsyncReturnType, TRPCError } from "@trpc/server";
 import { CreateNextContextOptions } from "@trpc/server/adapters/next";
+import type { PostHog } from "posthog-node";
 
 export type GetUserFn = (opts: CreateNextContextOptions) => Promise<{
   id: string;
@@ -12,6 +13,7 @@ export interface TRPCContextParams {
   emailClient: EmailClient;
   isSelfHosted: boolean;
   isEmailBlocked?: (email: string) => boolean;
+  posthogClient?: PostHog;
   /**
    * Takes a relative path and returns an absolute URL to the app
    * @param path

packages/backend/trpc/routers/polls.ts

@@ -626,6 +626,7 @@ export const polls = router({
         },
         select: {
           id: true,
+          createdAt: true,
           timeZone: true,
           title: true,
           location: true,
@@ -859,7 +860,23 @@ export const polls = router({
           });
         });
 
-        waitUntil(Promise.all([emailToHost, ...emailsToParticipants]));
+        ctx.posthogClient?.capture({
+          distinctId: ctx.user.id,
+          event: "finalize poll",
+          properties: {
+            number_of_participants: poll.participants.length,
+            number_of_attendees: attendees.length,
+            dayjs_since_created: dayjs().diff(poll.createdAt, "day"),
+          },
+        });
+
+        waitUntil(
+          Promise.all([
+            emailToHost,
+            ...emailsToParticipants,
+            ctx.posthogClient?.flushAsync(),
+          ]),
+        );
       }
     }),
   reopen: possiblyPublicProcedure