feat(analytics): extend analytics service with posthog-node SDK (#3637)

Extends the existing lib/services/analytics.js to wrap posthog-node :
- New config block analytics.posthog (enabled, apiKey, host, appTag,
  flushAt, flushInterval) gated by POSTHOG_ENABLED env var. Default off
  so existing downstream projects without env stay untouched.
- New service exports : identify(distinctId, properties),
  capture({ distinctId, event, properties }), shutdown(). Auto-injects
  app=appTag + env=NODE_ENV on every capture (custom properties win).
- Auth controller wires identify + capture(user_signed_up) on signup
  and capture(user_signed_in) on signin (generic events — downstream
  projects add their own business events on top).
- SIGTERM/SIGINT shutdown hook flushes pending events.
- 3 new test files covering identify, capture, lifecycle resilience.

Project-specific tagging via POSTHOG_APP_TAG=trawl|comes|... env var
in each downstream's deployment manifest. PostHog Cloud target
(https://eu.i.posthog.com default).

Author: PierreBrisorgueil

.env.example

@@ -10,7 +10,9 @@ DEVKIT_NODE_stripe_prices_pro_monthly=price_xxx
 DEVKIT_NODE_stripe_prices_pro_annual=price_xxx
 
 # PostHog Analytics
-# Get your keys from https://us.posthog.com/settings/project-api-key
+# Get your keys from https://eu.posthog.com/settings/project-api-key
+DEVKIT_NODE_posthog_enabled=true
 DEVKIT_NODE_posthog_apiKey=phc_xxx
-DEVKIT_NODE_posthog_host=https://us.i.posthog.com
+DEVKIT_NODE_posthog_host=https://eu.i.posthog.com
+DEVKIT_NODE_posthog_appTag=myproject
 DEVKIT_NODE_posthog_personalApiKey=phx_xxx

config/defaults/development.config.js

@@ -85,8 +85,12 @@ const config = {
     enabled: false,
   },
   posthog: {
+    enabled: false, // set to true + apiKey to activate (default off, no breakage on unconfigured projects)
     // apiKey: process.env.DEVKIT_NODE_posthog_apiKey ?? '',
-    // host: process.env.DEVKIT_NODE_posthog_host ?? 'https://us.i.posthog.com',
+    // host: process.env.DEVKIT_NODE_posthog_host ?? 'https://eu.i.posthog.com',
+    // appTag: process.env.DEVKIT_NODE_posthog_appTag ?? '', // e.g. 'trawl', 'comes' — auto-injected on every capture
+    flushAt: 20,
+    flushInterval: 10000,
     errorTracking: false, // opt-in: capture exceptions to PostHog (default: off)
     autoCapture: false, // opt-in: auto-capture api_request events (default: off)
   },

lib/services/analytics.js

@@ -9,22 +9,35 @@ import config from '../../config/index.js';
  */
 let client = null;
 
+/**
+ * Resolved at init time from config.posthog.appTag.
+ * Stored here so capture() doesn't re-read config on every call.
+ * @type {string|undefined}
+ */
+let _appTag;
+
 /**
  * Initialise the PostHog client using application config.
- * When `posthog.apiKey` is absent the service stays in no-op mode —
- * every public method silently returns without side-effects so that
- * downstream projects that don't use PostHog are never affected.
+ * When `posthog.enabled` is false OR `posthog.apiKey` is absent the service
+ * stays in no-op mode — every public method silently returns without
+ * side-effects so that downstream projects that don't use PostHog are
+ * never affected.
  *
  * The `posthog-node` SDK is lazy-loaded (dynamic import) so that
  * applications running on Node versions outside the SDK's engine
  * range never pay the import cost when analytics is unconfigured.
  * @returns {Promise<void>}
  */
 const init = async () => {
-  const { apiKey, host } = config.posthog ?? {};
-  if (!apiKey) return;
+  if (client) return; // already initialised — singleton guard
+  const { enabled, apiKey, host, flushAt, flushInterval, appTag } = config.posthog ?? {};
+  if (!enabled || !apiKey) return;
   const { PostHog } = await import('posthog-node');
-  client = new PostHog(apiKey, { host: host || 'https://us.i.posthog.com' });
+  const options = { host: host || 'https://eu.i.posthog.com' };
+  if (flushAt != null) options.flushAt = flushAt;
+  if (flushInterval != null) options.flushInterval = flushInterval;
+  client = new PostHog(apiKey, options);
+  _appTag = appTag;
 };
 
 /**
@@ -42,6 +55,30 @@ const track = (distinctId, event, properties, groups) => {
   } catch (_) { /* analytics must never break caller */ }
 };
 
+/**
+ * Capture an analytics event with automatic context injection.
+ * Auto-injects `app` (from config.posthog.appTag) and `env` (NODE_ENV)
+ * into every event. Custom properties take precedence over defaults.
+ * No-op when client is not initialised, distinctId or event are missing.
+ *
+ * @param {Object} params - Event parameters
+ * @param {string} params.distinctId - User or anonymous identifier
+ * @param {string} params.event - Event name
+ * @param {Object} [params.properties] - Additional event properties (win over defaults)
+ * @returns {void}
+ */
+const capture = ({ distinctId, event, properties = {} } = {}) => {
+  if (!client) return;
+  if (!distinctId || !event) return;
+  const defaults = {
+    env: process.env.NODE_ENV || 'development',
+    ...(_appTag ? { app: _appTag } : {}),
+  };
+  try {
+    client.capture({ distinctId, event, properties: { ...defaults, ...properties } });
+  } catch (_) { /* analytics must never break caller */ }
+};
+
 /**
  * Identify a user with optional properties.
  * @param {string} distinctId - User identifier
@@ -182,11 +219,13 @@ const shutdown = async () => {
   if (!client) return;
   await client.shutdown();
   client = null;
+  _appTag = undefined;
 };
 
 export default {
   init,
   track,
+  capture,
   identify,
   groupIdentify,
   getFeatureFlag,

lib/services/tests/analytics.capture.unit.tests.js

@@ -0,0 +1,245 @@
+/**
+ * Module dependencies.
+ */
+import { jest, beforeEach, afterEach, describe, test, expect } from '@jest/globals';
+
+/**
+ * Unit tests for AnalyticsService.capture() and enabled-flag behaviour.
+ */
+describe('Analytics capture() and enabled-flag:', () => {
+  let AnalyticsService;
+  let mockPostHogInstance;
+
+  beforeEach(async () => {
+    jest.resetModules();
+
+    mockPostHogInstance = {
+      capture: jest.fn(),
+      identify: jest.fn(),
+      groupIdentify: jest.fn(),
+      getFeatureFlag: jest.fn().mockResolvedValue(undefined),
+      isFeatureEnabled: jest.fn().mockResolvedValue(undefined),
+      shutdown: jest.fn().mockResolvedValue(undefined),
+    };
+
+    jest.unstable_mockModule('posthog-node', () => ({
+      PostHog: jest.fn().mockImplementation(() => mockPostHogInstance),
+    }));
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  // ─────────────────────────────────────────────────────────────────
+  // 1. enabled=false disables client creation
+  // ─────────────────────────────────────────────────────────────────
+  describe('enabled flag:', () => {
+    test('returns null client when enabled=false even if apiKey is present', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: false, apiKey: 'phc_test_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'test' });
+
+      const { PostHog } = await import('posthog-node');
+      expect(PostHog).not.toHaveBeenCalled();
+      expect(mockPostHogInstance.capture).not.toHaveBeenCalled();
+    });
+
+    test('returns null client when apiKey is missing even if enabled=true', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'test' });
+
+      const { PostHog } = await import('posthog-node');
+      expect(PostHog).not.toHaveBeenCalled();
+    });
+
+    test('creates client when enabled=true and apiKey is present', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_test_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+
+      const { PostHog } = await import('posthog-node');
+      expect(PostHog).toHaveBeenCalledWith('phc_test_key', expect.objectContaining({ host: 'https://eu.i.posthog.com' }));
+    });
+
+    test('passes flushAt and flushInterval to PostHog constructor', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com', flushAt: 20, flushInterval: 10000 } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+
+      const { PostHog } = await import('posthog-node');
+      expect(PostHog).toHaveBeenCalledWith('phc_key', {
+        host: 'https://eu.i.posthog.com',
+        flushAt: 20,
+        flushInterval: 10000,
+      });
+    });
+
+    test('singleton: two init() calls on the same module instance result in one PostHog client', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      await AnalyticsService.init(); // singleton guard: no-op, client already set
+
+      const { PostHog } = await import('posthog-node');
+      expect(PostHog).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  // ─────────────────────────────────────────────────────────────────
+  // 2. capture() no-ops
+  // ─────────────────────────────────────────────────────────────────
+  describe('capture() no-ops:', () => {
+    test('is a no-op when client is null', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: false, apiKey: 'phc_key' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'some_event' });
+
+      expect(mockPostHogInstance.capture).not.toHaveBeenCalled();
+    });
+
+    test('is a no-op when distinctId is missing', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      AnalyticsService.capture({ event: 'some_event' });
+
+      expect(mockPostHogInstance.capture).not.toHaveBeenCalled();
+    });
+
+    test('is a no-op when event is missing', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+
+      await AnalyticsService.init();
+      AnalyticsService.capture({ distinctId: 'user-1' });
+
+      expect(mockPostHogInstance.capture).not.toHaveBeenCalled();
+    });
+  });
+
+  // ─────────────────────────────────────────────────────────────────
+  // 3. capture() auto-injects app + env
+  // ─────────────────────────────────────────────────────────────────
+  describe('capture() property injection:', () => {
+    beforeEach(async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com', appTag: 'myapp' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+      await AnalyticsService.init();
+    });
+
+    test('auto-injects app from appTag and env from NODE_ENV', async () => {
+      const origEnv = process.env.NODE_ENV;
+      process.env.NODE_ENV = 'test';
+
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'my_event' });
+
+      expect(mockPostHogInstance.capture).toHaveBeenCalledWith({
+        distinctId: 'user-1',
+        event: 'my_event',
+        properties: { app: 'myapp', env: 'test' },
+      });
+
+      process.env.NODE_ENV = origEnv;
+    });
+
+    test('custom properties win over defaults', async () => {
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'my_event', properties: { app: 'override', custom: 'val' } });
+
+      expect(mockPostHogInstance.capture).toHaveBeenCalledWith({
+        distinctId: 'user-1',
+        event: 'my_event',
+        properties: expect.objectContaining({ app: 'override', custom: 'val' }),
+      });
+    });
+
+    test('does not inject app when appTag is not configured', async () => {
+      jest.resetModules();
+
+      jest.unstable_mockModule('posthog-node', () => ({
+        PostHog: jest.fn().mockImplementation(() => mockPostHogInstance),
+      }));
+
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+      await AnalyticsService.init();
+
+      AnalyticsService.capture({ distinctId: 'user-1', event: 'my_event' });
+
+      const call = mockPostHogInstance.capture.mock.calls[0][0];
+      expect(call.properties).not.toHaveProperty('app');
+      expect(call.properties).toHaveProperty('env');
+    });
+  });
+
+  // ─────────────────────────────────────────────────────────────────
+  // 4. shutdown idempotency
+  // ─────────────────────────────────────────────────────────────────
+  describe('shutdown idempotency:', () => {
+    test('two shutdown() calls invoke client.shutdown exactly once', async () => {
+      jest.unstable_mockModule('../../../config/index.js', () => ({
+        default: { posthog: { enabled: true, apiKey: 'phc_key', host: 'https://eu.i.posthog.com' } },
+      }));
+
+      const mod = await import('../analytics.js');
+      AnalyticsService = mod.default;
+      await AnalyticsService.init();
+
+      await AnalyticsService.shutdown();
+      await AnalyticsService.shutdown();
+
+      expect(mockPostHogInstance.shutdown).toHaveBeenCalledTimes(1);
+    });
+  });
+});

lib/services/tests/analytics.forRequest.unit.tests.js

@@ -34,7 +34,7 @@ describe('analytics request-aware feature-flag helpers:', () => {
     }));
 
     jest.unstable_mockModule('../../../config/index.js', () => ({
-      default: { posthog: { apiKey: 'phk_test', host: 'https://posthog.test' } },
+      default: { posthog: { enabled: true, apiKey: 'phk_test', host: 'https://posthog.test' } },
     }));
 
     const mod = await import('../analytics.js');