feat(events): New API EppoAssignmentLogger

src/client/eppo-client.ts

@@ -1171,10 +1171,19 @@ export default class EppoClient {
   }
 
   private maybeLogAssignment(result: FlagEvaluation) {
-    const { flagKey, format, subjectKey, allocationKey, subjectAttributes, variation } = result;
+    const {
+      flagKey,
+      format,
+      subjectKey,
+      allocationKey = null,
+      subjectAttributes,
+      variation,
+      flagEvaluationDetails,
+      extraLogging = {},
+    } = result;
     const event: IAssignmentEvent = {
-      ...(result.extraLogging ?? {}),
-      allocation: allocationKey ?? null,
+      ...extraLogging,
+      allocation: allocationKey,
       experiment: allocationKey ? `${flagKey}-${allocationKey}` : null,
       featureFlag: flagKey,
       format,
@@ -1183,7 +1192,7 @@ export default class EppoClient {
       timestamp: new Date().toISOString(),
       subjectAttributes,
       metaData: this.buildLoggerMetadata(),
-      evaluationDetails: result.flagEvaluationDetails,
+      evaluationDetails: flagEvaluationDetails,
     };
 
     if (variation && allocationKey) {

src/eppo-assignment-logger.ts

@@ -0,0 +1,26 @@
+import { IAssignmentEvent, IAssignmentLogger } from './assignment-logger';
+import EppoClient from './client/eppo-client';
+
+/** TODO docs */
+export class EppoAssignmentLogger implements IAssignmentLogger {
+  constructor(private readonly eppoClient: EppoClient) {}
+
+  logAssignment(event: IAssignmentEvent): void {
+    const entity = event.subjectAttributes.entity;
+    const {
+      holdoutKey: holdout,
+      holdoutVariation: holdout_variant,
+      subject: subject_id,
+      experiment,
+      variant,
+    } = event;
+    this.eppoClient.track('__eppo_assignment', {
+      subject_id,
+      experiment,
+      variant,
+      entity,
+      holdout,
+      holdout_variant,
+    });
+  }
+}