feat(backend): Added skeleton for a database learning object/path provider.

backend/src/services/learning-objects/database-learning-object-provider.ts

@@ -0,0 +1,42 @@
+import {LearningObjectProvider} from "./learning-object-provider";
+import {
+    FilteredLearningObject,
+    LearningObjectIdentifier,
+    LearningPathIdentifier
+} from "../../interfaces/learning-content";
+
+/**
+ * Service providing access to data about learning objects from the database
+ */
+const databaseLearningObjectProvider: LearningObjectProvider = {
+    /**
+     * Fetches a single learning object by its HRUID
+     */
+    getLearningObjectById(id: LearningObjectIdentifier): Promise<FilteredLearningObject | null> {
+        return Promise.resolve(null); // TODO
+    },
+
+    /**
+     * Fetch full learning object data (metadata)
+     */
+    getLearningObjectHTML(id: LearningObjectIdentifier): Promise<string | null> {
+        return Promise.resolve(null); // TODO
+    },
+
+    /**
+     * Fetch only learning object HRUIDs
+     */
+    getLearningObjectIdsFromPath(id: LearningPathIdentifier): Promise<string[]> {
+        return Promise.resolve([]);// TODO
+    },
+
+    /**
+     * Obtain a HTML-rendering of the learning object with the given identifier (as a string).
+     */
+    getLearningObjectsFromPath(id: LearningPathIdentifier): Promise<FilteredLearningObject[]> {
+        return Promise.resolve([]); // TODO
+    }
+
+}
+
+export default databaseLearningObjectProvider;