[PM-2282] Make feature flags type safe (#8612)

Refactors the feature flags in ConfigService to be type safe. It also moves the default value to a centralized location rather than the caller defining it. This ensures consistency across the various places they are used.

libs/common/src/platform/abstractions/config/config.service.ts

@@ -1,7 +1,7 @@
 import { Observable } from "rxjs";
 import { SemVer } from "semver";
 
-import { FeatureFlag } from "../../../enums/feature-flag.enum";
+import { FeatureFlag, FeatureFlagValueType } from "../../../enums/feature-flag.enum";
 import { Region } from "../environment.service";
 
 import { ServerConfig } from "./server-config";
@@ -14,23 +14,15 @@ export abstract class ConfigService {
   /**
    * Retrieves the value of a feature flag for the currently active user
    * @param key The feature flag to retrieve
-   * @param defaultValue The default value to return if the feature flag is not set or the server's config is irretrievable
    * @returns An observable that emits the value of the feature flag, updates as the server config changes
    */
-  getFeatureFlag$: <T extends boolean | number | string>(
-    key: FeatureFlag,
-    defaultValue?: T,
-  ) => Observable<T>;
+  getFeatureFlag$: <Flag extends FeatureFlag>(key: Flag) => Observable<FeatureFlagValueType<Flag>>;
   /**
    * Retrieves the value of a feature flag for the currently active user
    * @param key The feature flag to retrieve
-   * @param defaultValue The default value to return if the feature flag is not set or the server's config is irretrievable
    * @returns The value of the feature flag
    */
-  getFeatureFlag: <T extends boolean | number | string>(
-    key: FeatureFlag,
-    defaultValue?: T,
-  ) => Promise<T>;
+  getFeatureFlag: <Flag extends FeatureFlag>(key: Flag) => Promise<FeatureFlagValueType<Flag>>;
   /**
    * Verifies whether the server version meets the minimum required version
    * @param minimumRequiredServerVersion The minimum version required

libs/common/src/platform/abstractions/config/server-config.ts

@@ -1,5 +1,6 @@
 import { Jsonify } from "type-fest";
 
+import { AllowedFeatureFlagTypes } from "../../../enums/feature-flag.enum";
 import {
   ServerConfigData,
   ThirdPartyServerConfigData,
@@ -14,7 +15,7 @@ export class ServerConfig {
   server?: ThirdPartyServerConfigData;
   environment?: EnvironmentServerConfigData;
   utcDate: Date;
-  featureStates: { [key: string]: string } = {};
+  featureStates: { [key: string]: AllowedFeatureFlagTypes } = {};
 
   constructor(serverConfigData: ServerConfigData) {
     this.version = serverConfigData.version;

libs/common/src/platform/models/data/server-config.data.ts

@@ -1,5 +1,6 @@
 import { Jsonify } from "type-fest";
 
+import { AllowedFeatureFlagTypes } from "../../../enums/feature-flag.enum";
 import { Region } from "../../abstractions/environment.service";
 import {
   ServerConfigResponse,
@@ -13,7 +14,7 @@ export class ServerConfigData {
   server?: ThirdPartyServerConfigData;
   environment?: EnvironmentServerConfigData;
   utcDate: string;
-  featureStates: { [key: string]: string } = {};
+  featureStates: { [key: string]: AllowedFeatureFlagTypes } = {};
 
   constructor(serverConfigResponse: Partial<ServerConfigResponse>) {
     this.version = serverConfigResponse?.version;

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

@@ -13,7 +13,11 @@ import {
 } from "rxjs";
 import { SemVer } from "semver";
 
-import { FeatureFlag, FeatureFlagValue } from "../../../enums/feature-flag.enum";
+import {
+  DefaultFeatureFlagValue,
+  FeatureFlag,
+  FeatureFlagValueType,
+} from "../../../enums/feature-flag.enum";
 import { UserId } from "../../../types/guid";
 import { ConfigApiServiceAbstraction } from "../../abstractions/config/config-api.service.abstraction";
 import { ConfigService } from "../../abstractions/config/config.service";
@@ -89,20 +93,21 @@ export class DefaultConfigService implements ConfigService {
       map((config) => config?.environment?.cloudRegion ?? Region.US),
     );
   }
-  getFeatureFlag$<T extends FeatureFlagValue>(key: FeatureFlag, defaultValue?: T) {
+
+  getFeatureFlag$<Flag extends FeatureFlag>(key: Flag) {
     return this.serverConfig$.pipe(
       map((serverConfig) => {
         if (serverConfig?.featureStates == null || serverConfig.featureStates[key] == null) {
-          return defaultValue;
+          return DefaultFeatureFlagValue[key];
         }
 
-        return serverConfig.featureStates[key] as T;
+        return serverConfig.featureStates[key] as FeatureFlagValueType<Flag>;
       }),
     );
   }
 
-  async getFeatureFlag<T extends FeatureFlagValue>(key: FeatureFlag, defaultValue?: T) {
-    return await firstValueFrom(this.getFeatureFlag$(key, defaultValue));
+  async getFeatureFlag<Flag extends FeatureFlag>(key: Flag) {
+    return await firstValueFrom(this.getFeatureFlag$(key));
   }
 
   checkServerMeetsVersionRequirement$(minimumRequiredServerVersion: SemVer) {