Selki/ff3396 expiring bandit cache (#80)

* Switched to Expiring LRU cache for bandit actions

* Expiring bandit cache

* linter

* bandit cache tests fix

Author: maya-the-mango

src/index.spec.ts

@@ -11,6 +11,7 @@ import {
 } from '@eppo/js-client-sdk-common';
 import { BanditParameters, BanditVariation } from '@eppo/js-client-sdk-common/dist/interfaces';
 import { ContextAttributes } from '@eppo/js-client-sdk-common/dist/types';
+import { Attributes } from '@eppo/js-client-sdk-common/src/types';
 import * as td from 'testdouble';
 
 import apiServer, { TEST_BANDIT_API_KEY, TEST_SERVER_PORT } from '../test/mockApiServer';
@@ -27,6 +28,8 @@ import {
 
 import { getInstance, IAssignmentEvent, IAssignmentLogger, init } from '.';
 
+import SpyInstance = jest.SpyInstance;
+
 const { DEFAULT_POLL_INTERVAL_MS, POLL_JITTER_PCT } = constants;
 
 const apiKey = 'zCsQuoHJxVPp895.ZWg9MTIzNDU2LmUudGVzdGluZy5lcHBvLmNsb3Vk';
@@ -313,6 +316,90 @@ describe('EppoClient E2E test', () => {
       // Ensure that this test case correctly checked some test assignments
       expect(numAssignmentsChecked).toBeGreaterThan(0);
     });
+
+    describe('Bandit assignment cache', () => {
+      const flagKey = 'banner_bandit_flag'; // piggyback off a shared test data flag
+      const bobKey = 'bob';
+      const bobAttributes: Attributes = { age: 25, country: 'USA', gender_identity: 'female' };
+      const bobActions: Record<string, Attributes> = {
+        nike: { brand_affinity: 1.5, loyalty_tier: 'silver' },
+        adidas: { brand_affinity: -1.0, loyalty_tier: 'bronze' },
+        reebok: { brand_affinity: 0.5, loyalty_tier: 'gold' },
+      };
+
+      const aliceKey = 'alice';
+      const aliceAttributes: Attributes = { age: 25, country: 'USA', gender_identity: 'female' };
+      const aliceActions: Record<string, Attributes> = {
+        nike: { brand_affinity: 1.5, loyalty_tier: 'silver' },
+        adidas: { brand_affinity: -1.0, loyalty_tier: 'bronze' },
+        reebok: { brand_affinity: 0.5, loyalty_tier: 'gold' },
+      };
+      const charlieKey = 'charlie';
+      const charlieAttributes: Attributes = { age: 25, country: 'USA', gender_identity: 'female' };
+      const charlieActions: Record<string, Attributes> = {
+        nike: { brand_affinity: 1.0, loyalty_tier: 'gold' },
+        adidas: { brand_affinity: 1.0, loyalty_tier: 'silver' },
+        puma: {},
+      };
+
+      let banditLoggerSpy: SpyInstance<void, [banditEvent: IBanditEvent]>;
+      const defaultBanditCacheTTL = 600_000;
+
+      beforeAll(async () => {
+        const dummyBanditLogger: IBanditLogger = {
+          logBanditAction(banditEvent: IBanditEvent) {
+            console.log(
+              `Bandit ${banditEvent.bandit} assigned ${banditEvent.subject} the action ${banditEvent.action}`,
+            );
+          },
+        };
+        banditLoggerSpy = jest.spyOn(dummyBanditLogger, 'logBanditAction');
+        await init({
+          apiKey: TEST_BANDIT_API_KEY, // Flag to dummy test server we want bandit-related files
+          baseUrl: `http://127.0.0.1:${TEST_SERVER_PORT}`,
+          assignmentLogger: mockLogger,
+          banditLogger: dummyBanditLogger,
+        });
+      });
+
+      it('Should not log bandit assignment if cached version is still valid', async () => {
+        const client = getInstance();
+        client.useExpiringInMemoryBanditAssignmentCache(2);
+
+        // Let's say someone is rage refreshing - we want to log assignment only once
+        for (const _ of Array(3).keys()) {
+          client.getBanditAction(flagKey, bobKey, bobAttributes, bobActions, 'default');
+        }
+        expect(banditLoggerSpy).toHaveBeenCalledTimes(1);
+      });
+      it('Should log bandit assignment if cached entry is expired', async () => {
+        jest.useFakeTimers();
+        banditLoggerSpy.mockReset();
+
+        const client = getInstance();
+        client.useExpiringInMemoryBanditAssignmentCache(2);
+
+        client.getBanditAction(flagKey, bobKey, bobAttributes, bobActions, 'default');
+        jest.advanceTimersByTime(defaultBanditCacheTTL);
+        client.getBanditAction(flagKey, bobKey, bobAttributes, bobActions, 'default');
+        expect(banditLoggerSpy).toHaveBeenCalledTimes(2);
+      });
+
+      it('Should invalidate least used cache entry if cache reaches max size', async () => {
+        banditLoggerSpy.mockReset();
+        const client = getInstance();
+        client.useExpiringInMemoryBanditAssignmentCache(2);
+
+        client.getBanditAction(flagKey, bobKey, bobAttributes, bobActions, 'default');
+        client.getBanditAction(flagKey, aliceKey, aliceAttributes, aliceActions, 'default');
+        client.getBanditAction(flagKey, charlieKey, charlieAttributes, charlieActions, 'default');
+        // even though bob was called 2nd time within cache validity time
+        // we expect assignment to be logged because max cache size is 2
+        // and currently storing alice and charlie
+        client.getBanditAction(flagKey, bobKey, bobAttributes, bobActions, 'default');
+        expect(banditLoggerSpy).toHaveBeenCalledTimes(4);
+      });
+    });
   });
 
   describe('initialization errors', () => {