refactor(backend): Preparation for learning content from multiple data sources.

Refactored the service layer so that it becomes possible to add another source for learning objects and learning paths.

backend/src/services/learning-content/learning-object-service.ts

@@ -0,0 +1,30 @@
+import {FilteredLearningObject} from "../../interfaces/learningContent";
+import dwengoApiLearningObjectProvider from "./dwengo-api/dwengo-api-learning-object-provider";
+
+/**
+ * Service providing access to data about learning objects from the appropriate data source (database or Dwengo-api)
+ */
+const learningObjectService = {
+    /**
+     * Fetches a single learning object by its HRUID
+     */
+    getLearningObjectById(hruid: string, language: string): Promise<FilteredLearningObject | null> {
+        return dwengoApiLearningObjectProvider.getLearningObjectById(hruid, language);
+    },
+
+    /**
+     * Fetch full learning object data (metadata)
+     */
+    getLearningObjectsFromPath(hruid: string, language: string): Promise<FilteredLearningObject[]> {
+        return dwengoApiLearningObjectProvider.getLearningObjectsFromPath(hruid, language);
+    },
+
+    /**
+     * Fetch only learning object HRUIDs
+     */
+    getLearningObjectIdsFromPath(hruid: string, language: string): Promise<string[]> {
+        return dwengoApiLearningObjectProvider.getLearningObjectIdsFromPath(hruid, language);
+    }
+};
+
+export default learningObjectService;