From fef53e5737f3e7262beb35b6f575be804bac523f Mon Sep 17 00:00:00 2001
From: Brian Giori <brian.giori@amplitude.com>
Date: Tue, 15 Oct 2024 14:23:08 -0700
Subject: [PATCH] feat: track impressions for web experiments (#127)

---
 .../src/integration/manager.ts                | 25 +++++++++--
 .../experiment-browser/test/client.test.ts    | 44 ++++++++++---------
 .../test/integration/manager.test.ts          | 21 +++++++++
 3 files changed, 67 insertions(+), 23 deletions(-)

diff --git a/packages/experiment-browser/src/integration/manager.ts b/packages/experiment-browser/src/integration/manager.ts
index 2f4994e..d8508aa 100644
--- a/packages/experiment-browser/src/integration/manager.ts
+++ b/packages/experiment-browser/src/integration/manager.ts
@@ -96,11 +96,30 @@ export class IntegrationManager {
    */
   track(exposure: Exposure): void {
     if (this.cache.shouldTrack(exposure)) {
-      this.queue.push({
-        eventType: '$exposure',
+      const event = this.getExposureEvent(exposure);
+      this.queue.push(event);
+    }
+  }
+
+  private getExposureEvent(exposure: Exposure): ExperimentEvent {
+    let event: ExperimentEvent = {
+      eventType: '$exposure',
+      eventProperties: exposure,
+    };
+    if (exposure.metadata?.exposureEvent) {
+      // Metadata specifically passes the exposure event definition
+      event = {
+        eventType: exposure.metadata?.exposureEvent as string,
+        eventProperties: exposure,
+      };
+    } else if (exposure.metadata?.deliveryMethod === 'web') {
+      // Web experiments track impression events by default
+      event = {
+        eventType: '$impression',
         eventProperties: exposure,
-      });
+      };
     }
+    return event;
   }
 }
 
diff --git a/packages/experiment-browser/test/client.test.ts b/packages/experiment-browser/test/client.test.ts
index 4e7a81f..235e9f5 100644
--- a/packages/experiment-browser/test/client.test.ts
+++ b/packages/experiment-browser/test/client.test.ts
@@ -676,26 +676,30 @@ describe('variant fallbacks', () => {
       expect(spy.mock.calls[0][0].variant).toBeUndefined();
     });
 
-    test('default variant returned when no other fallback is provided', async () => {
-      const user = {};
-      const exposureTrackingProvider = new TestExposureTrackingProvider();
-      const spy = jest.spyOn(exposureTrackingProvider, 'track');
-      const client = new ExperimentClient(API_KEY, {
-        exposureTrackingProvider: exposureTrackingProvider,
-        source: Source.LocalStorage,
-        fetchOnStart: true,
-      });
-      mockClientStorage(client);
-      // Start and fetch
-      await client.start(user);
-      const variant = client.variant('sdk-ci-test');
-      expect(variant.key).toEqual('off');
-      expect(variant.value).toBeUndefined();
-      expect(variant.metadata?.default).toEqual(true);
-      expect(spy).toHaveBeenCalledTimes(1);
-      expect(spy.mock.calls[0][0].flag_key).toEqual('sdk-ci-test');
-      expect(spy.mock.calls[0][0].variant).toBeUndefined();
-    });
+    test(
+      'default variant returned when no other fallback is provided',
+      async () => {
+        const user = {};
+        const exposureTrackingProvider = new TestExposureTrackingProvider();
+        const spy = jest.spyOn(exposureTrackingProvider, 'track');
+        const client = new ExperimentClient(API_KEY, {
+          exposureTrackingProvider: exposureTrackingProvider,
+          source: Source.LocalStorage,
+          fetchOnStart: true,
+        });
+        mockClientStorage(client);
+        // Start and fetch
+        await client.start(user);
+        const variant = client.variant('sdk-ci-test');
+        expect(variant.key).toEqual('off');
+        expect(variant.value).toBeUndefined();
+        expect(variant.metadata?.default).toEqual(true);
+        expect(spy).toHaveBeenCalledTimes(1);
+        expect(spy.mock.calls[0][0].flag_key).toEqual('sdk-ci-test');
+        expect(spy.mock.calls[0][0].variant).toBeUndefined();
+      },
+      10 * 1000,
+    );
   });
 
   describe('initial variants source', () => {
diff --git a/packages/experiment-browser/test/integration/manager.test.ts b/packages/experiment-browser/test/integration/manager.test.ts
index f12f47d..e93fe8a 100644
--- a/packages/experiment-browser/test/integration/manager.test.ts
+++ b/packages/experiment-browser/test/integration/manager.test.ts
@@ -178,6 +178,27 @@ describe('IntegrationManager', () => {
         },
       });
     });
+    test('web exposure tracked as impression', () => {
+      manager.track({
+        flag_key: 'flag-key',
+        variant: 'treatment',
+        experiment_key: 'exp-1',
+        metadata: {
+          deliveryMethod: 'web',
+        },
+      });
+      expect(manager['queue']['inMemoryQueue'][0]).toEqual({
+        eventType: '$impression',
+        eventProperties: {
+          flag_key: 'flag-key',
+          variant: 'treatment',
+          experiment_key: 'exp-1',
+          metadata: {
+            deliveryMethod: 'web',
+          },
+        },
+      });
+    });
   });
 });