feat(datadog): Add support for getting RUM metrics for the TypeScript…

… client (#65)

* feat(datadog): Add support for getting RUM metrics for the TypeScript client

* chore(README.md): Add missing import in README example

* chore(README.md): add instructions on how to install datadog RUM

flipt-node/README.md

@@ -17,3 +17,48 @@ npm i @flipt-io/flipt@{version}
 ## Usage
 
 In the [example](./example) directory, there is an example TypeScript program which imports in the flipt client, and uses it appropriately, please refer to that for how to use the client.
+
+### Metrics
+
+There is support for [Datadog RUM](https://docs.datadoghq.com/real_user_monitoring/) through this client. This allows you to track the values of feature flag evaluation and how it relates to active browser sessions.
+
+You can first install the datadog RUM client like so:
+
+```
+npm install --save @datadog/browser-rum
+```
+
+To start tracking feature flags on Datadog:
+
+```typescript
+import { datadogRum } from '@datadog/browser-rum';
+import { FliptClient, FliptMetrics } from '@flipt-io/flipt';
+
+datadogRum.init({
+  applicationId: '<APPLICATION_ID>',
+  clientToken: '<CLIENT_TOKEN>',
+  site: 'datadoghq.com',
+  service:'<SERVICE_NAME>',
+  env:'<ENV_NAME>',
+  enableExperimentalFeatures: ["feature_flags"],
+  sessionSampleRate:100,
+  sessionReplaySampleRate: 20,
+  trackUserInteractions: true,
+  trackResources: true,
+  trackLongTasks: true,
+  defaultPrivacyLevel:'mask-user-input'
+});
+
+datadogRum.startSessionReplayRecording();
+
+const metricsClient = new FliptMetrics(new FliptClient({
+  url: "http://localhost:8080",
+}).evaluation, datadogRum);
+
+const response = await metricsClient.variant({
+  namespaceKey: "default",
+  flagKey: "hello-this",
+  entityId: uuidv4(),
+  context: {},
+});
+```

flipt-node/src/index.ts

@@ -1,4 +1,9 @@
 import { Evaluation } from "./evaluation";
+import {
+  BooleanEvaluationResponse,
+  EvaluationRequest,
+  VariantEvaluationResponse
+} from "./evaluation/models";
 
 interface FliptClientOptions {
   url?: string;
@@ -66,3 +71,37 @@ export class FliptClient {
     );
   }
 }
+
+export class FliptMetrics {
+  evaluationClient: Evaluation;
+  datadogRum: any;
+
+  constructor(evaluationClient: Evaluation, datadogRum: any) {
+    this.evaluationClient = evaluationClient;
+    this.datadogRum = datadogRum;
+  }
+
+  public async boolean(
+    request: EvaluationRequest
+  ): Promise<BooleanEvaluationResponse> {
+    const response = await this.evaluationClient.boolean(request);
+
+    this.datadogRum.addFeatureFlagEvaluation(
+      `${request.namespaceKey}/${request.flagKey}`,
+      response.enabled
+    );
+    return response;
+  }
+
+  public async variant(
+    request: EvaluationRequest
+  ): Promise<VariantEvaluationResponse> {
+    const response = await this.evaluationClient.variant(request);
+
+    this.datadogRum.addFeatureFlagEvaluation(
+      `${request.namespaceKey}/${request.flagKey}`,
+      response.variantKey
+    );
+    return response;
+  }
+}