Last one wins flag providers (#40)

* last feature flag wins

* fix lint

Author: zhiyuanliang-ms

src/featureProvider.ts

@@ -28,7 +28,7 @@ export class ConfigurationMapFeatureFlagProvider implements IFeatureFlagProvider
     }
     async getFeatureFlag(featureName: string): Promise<FeatureFlag | undefined> {
         const featureConfig = this.#configuration.get<FeatureManagementConfiguration>(FEATURE_MANAGEMENT_KEY);
-        return featureConfig?.[FEATURE_FLAGS_KEY]?.find((feature) => feature.id === featureName);
+        return featureConfig?.[FEATURE_FLAGS_KEY]?.findLast((feature) => feature.id === featureName);
     }
 
     async getFeatureFlags(): Promise<FeatureFlag[]> {
@@ -49,7 +49,7 @@ export class ConfigurationObjectFeatureFlagProvider implements IFeatureFlagProvi
 
     async getFeatureFlag(featureName: string): Promise<FeatureFlag | undefined> {
         const featureFlags = this.#configuration[FEATURE_MANAGEMENT_KEY]?.[FEATURE_FLAGS_KEY];
-        return featureFlags?.find((feature: FeatureFlag) => feature.id === featureName);
+        return featureFlags?.findLast((feature: FeatureFlag) => feature.id === featureName);
     }
 
     async getFeatureFlags(): Promise<FeatureFlag[]> {

test/featureManager.test.ts

@@ -72,6 +72,36 @@ describe("feature manager", () => {
         ]);
     });
 
+    it("should let the last feature flag win", () => {
+        const jsonObject = {
+            "feature_management": {
+                "feature_flags": [
+                    { "id": "Alpha", "description": "", "enabled": false, "conditions": { "client_filters": [] } },
+                    { "id": "Alpha", "description": "", "enabled": true, "conditions": { "client_filters": [] } }
+                ]
+            }
+        };
+
+        const provider1 = new ConfigurationObjectFeatureFlagProvider(jsonObject);
+        const featureManager1 = new FeatureManager(provider1);
+
+        const dataSource = new Map();
+        dataSource.set("feature_management", {
+            feature_flags: [
+                { "id": "Alpha", "description": "", "enabled": false, "conditions": { "client_filters": [] } },
+                { "id": "Alpha", "description": "", "enabled": true, "conditions": { "client_filters": [] } }
+            ],
+        });
+
+        const provider2 = new ConfigurationMapFeatureFlagProvider(dataSource);
+        const featureManager2 = new FeatureManager(provider2);
+
+        return Promise.all([
+            expect(featureManager1.isEnabled("Alpha")).eventually.eq(true),
+            expect(featureManager2.isEnabled("Alpha")).eventually.eq(true)
+        ]);
+    });
+
     it("should evaluate features with conditions");
     it("should override default filters with custom filters");
 });