Implement overrides store functionality

src/configuration-factory.ts

@@ -5,6 +5,7 @@ import {
   MemoryOnlyConfigurationStore,
   MemoryStore,
   PrecomputedFlag,
+  Variation,
 } from '@eppo/js-client-sdk-common';
 
 import ChromeStorageAsyncMap from './cache/chrome-storage-async-map';
@@ -14,6 +15,7 @@ import {
   ServingStoreUpdateStrategy,
 } from './isolatable-hybrid.store';
 import { LocalStorageEngine } from './local-storage-engine';
+import { OVERRIDES_SUFFIX_KEY } from './storage-key-constants';
 import { StringValuedAsyncStore } from './string-valued.store';
 
 export function precomputedFlagsStorageFactory(): IConfigurationStore<PrecomputedFlag> {
@@ -79,6 +81,33 @@ export function configurationStorageFactory(
   return new MemoryOnlyConfigurationStore();
 }
 
+export function overridesStorageFactory(
+  {
+    hasWindowLocalStorage = false,
+    forceMemoryOnly = false,
+  }: {
+    hasWindowLocalStorage?: boolean;
+    forceMemoryOnly?: boolean;
+  },
+  {
+    windowLocalStorage,
+  }: {
+    windowLocalStorage?: Storage;
+  } = {},
+): IConfigurationStore<Variation> {
+  if (forceMemoryOnly) {
+    return new MemoryOnlyConfigurationStore();
+  } else if (hasWindowLocalStorage && windowLocalStorage) {
+    const localStorageEngine = new LocalStorageEngine(windowLocalStorage, OVERRIDES_SUFFIX_KEY);
+    return new IsolatableHybridConfigurationStore(
+      new MemoryStore<Variation>(),
+      new StringValuedAsyncStore<Variation>(localStorageEngine),
+      'always',
+    );
+  }
+  return new MemoryOnlyConfigurationStore();
+}
+
 export function hasChromeStorage(): boolean {
   return typeof chrome !== 'undefined' && !!chrome.storage;
 }

src/index.ts

@@ -29,6 +29,7 @@ import {
   hasChromeStorage,
   hasWindowLocalStorage,
   localStorageIfAvailable,
+  overridesStorageFactory,
 } from './configuration-factory';
 import BrowserNetworkStatusListener from './events/browser-network-status-listener';
 import LocalStorageBackedNamedEventQueue from './events/local-storage-backed-named-event-queue';
@@ -67,6 +68,16 @@ const flagConfigurationStore = configurationStorageFactory({
   forceMemoryOnly: true,
 });
 
+// Create the overrides store
+const overridesStore = overridesStorageFactory(
+  {
+    hasWindowLocalStorage: hasWindowLocalStorage(),
+  },
+  {
+    windowLocalStorage: localStorageIfAvailable(),
+  },
+);
+
 // Instantiate the precomputed flgas store with memory-only implementation.
 const memoryOnlyPrecomputedFlagsStore = precomputedFlagsStorageFactory();
 
@@ -81,6 +92,7 @@ export class EppoJSClient extends EppoClient {
   public static instance = new EppoJSClient({
     flagConfigurationStore,
     isObfuscated: true,
+    overridesStore,
   });
   public static initialized = false;
 
@@ -278,6 +290,17 @@ export function offlineInit(config: IClientConfigSync): EppoClient {
       );
     EppoJSClient.instance.setFlagConfigurationStore(memoryOnlyConfigurationStore);
 
+    // Create and set up the overrides store
+    const overridesStore = overridesStorageFactory(
+      {
+        hasWindowLocalStorage: hasWindowLocalStorage(),
+      },
+      {
+        windowLocalStorage: localStorageIfAvailable(),
+      },
+    );
+    EppoJSClient.instance.setOverridesStore(overridesStore);
+
     // Allow the caller to override the default obfuscated mode, which is false
     // since the purpose of this method is to bootstrap the SDK from an external source,
     // which is likely a server that has not-obfuscated flag values.
@@ -380,6 +403,17 @@ export async function init(config: IClientConfig): Promise<EppoClient> {
     );
     instance.setFlagConfigurationStore(configurationStore);
 
+    const overridesStore = overridesStorageFactory(
+      {
+        hasWindowLocalStorage: hasWindowLocalStorage(),
+      },
+      {
+        windowLocalStorage: localStorageIfAvailable(),
+      },
+    );
+    instance.setOverridesStore(overridesStore);
+    overridesStore.init();
+
     // instantiate and init assignment cache
     const assignmentCache = assignmentCacheFactory({
       chromeStorage: chromeStorageIfAvailable(),

src/storage-key-constants.ts

@@ -1,2 +1,3 @@
 export const CONFIGURATION_KEY = 'eppo-configuration';
 export const META_KEY = 'eppo-configuration-meta';
+export const OVERRIDES_SUFFIX_KEY = 'overrides';