[PM-11661]Add New Reseed - Fill Buffer Behind Feature Flag (#10905)

* Add New Reseed - Fill Buffer Behind Feature Flag

* Add Tests

* Lint

libs/common/src/platform/services/config/config.service.spec.ts

@@ -16,6 +16,7 @@ import {
 import { subscribeTo } from "../../../../spec/observable-tracker";
 import { AuthService } from "../../../auth/abstractions/auth.service";
 import { AuthenticationStatus } from "../../../auth/enums/authentication-status";
+import { FeatureFlag } from "../../../enums/feature-flag.enum";
 import { UserId } from "../../../types/guid";
 import { ConfigApiServiceAbstraction } from "../../abstractions/config/config-api.service.abstraction";
 import { ServerConfig } from "../../abstractions/config/server-config";
@@ -277,6 +278,48 @@ describe("ConfigService", () => {
     });
   });
 
+  describe("userCachedFeatureFlag$", () => {
+    it("maps saved user config to a feature flag", async () => {
+      const updateFeature = (value: boolean) => {
+        return new ServerConfig(
+          new ServerConfigData({
+            featureStates: {
+              "test-feature": value,
+            },
+          }),
+        );
+      };
+
+      const configService = new DefaultConfigService(
+        configApiService,
+        environmentService,
+        logService,
+        stateProvider,
+        authService,
+      );
+
+      userState.nextState(null);
+
+      const promise = firstValueFrom(
+        configService
+          .userCachedFeatureFlag$("test-feature" as FeatureFlag, userId)
+          .pipe(bufferCount(3)),
+      );
+
+      userState.nextState(updateFeature(true));
+      userState.nextState(updateFeature(false));
+
+      const values = await promise;
+
+      // We wouldn't normally expect this to be undefined, the logic
+      // should normally return the feature flags default value but since
+      // we are faking a feature flag key, undefined is expected
+      expect(values[0]).toBe(undefined);
+      expect(values[1]).toBe(true);
+      expect(values[2]).toBe(false);
+    });
+  });
+
   describe("slow configuration", () => {
     const environmentSubject = new BehaviorSubject<Environment>(null);
 

libs/common/src/platform/services/config/default-config.service.ts

@@ -115,16 +115,27 @@ export class DefaultConfigService implements ConfigService {
 
   getFeatureFlag$<Flag extends FeatureFlag>(key: Flag) {
     return this.serverConfig$.pipe(
-      map((serverConfig) => {
-        if (serverConfig?.featureStates == null || serverConfig.featureStates[key] == null) {
-          return DefaultFeatureFlagValue[key];
-        }
-
-        return serverConfig.featureStates[key] as FeatureFlagValueType<Flag>;
-      }),
+      map((serverConfig) => this.getFeatureFlagValue(serverConfig, key)),
     );
   }
 
+  private getFeatureFlagValue<Flag extends FeatureFlag>(
+    serverConfig: ServerConfig | null,
+    flag: Flag,
+  ) {
+    if (serverConfig?.featureStates == null || serverConfig.featureStates[flag] == null) {
+      return DefaultFeatureFlagValue[flag];
+    }
+
+    return serverConfig.featureStates[flag] as FeatureFlagValueType<Flag>;
+  }
+
+  userCachedFeatureFlag$<Flag extends FeatureFlag>(key: Flag, userId: UserId) {
+    return this.stateProvider
+      .getUser(userId, USER_SERVER_CONFIG)
+      .state$.pipe(map((config) => this.getFeatureFlagValue(config, key)));
+  }
+
   async getFeatureFlag<Flag extends FeatureFlag>(key: Flag) {
     return await firstValueFrom(this.getFeatureFlag$(key));
   }