feat(backend): Added endpoint to fetch HTML version of learning object (from Dwengo backend)

Also refactored a bit to make this easier.

backend/src/controllers/learning-paths.ts

@@ -0,0 +1,53 @@
+import { Request, Response } from 'express';
+import { themes } from '../data/themes.js';
+import { FALLBACK_LANG } from '../config.js';
+import learningPathService from "../services/learning-content/learning-path-service";
+import {NotFoundException} from "../exceptions";
+
+/**
+ * Fetch learning paths based on query parameters.
+ */
+export async function getLearningPaths(
+    req: Request,
+    res: Response
+): Promise<void> {
+    const hruids = req.query.hruid;
+    const themeKey = req.query.theme as string;
+    const searchQuery = req.query.search as string;
+    const language = (req.query.language as string) || FALLBACK_LANG;
+
+    let hruidList;
+
+    if (hruids) {
+        hruidList = Array.isArray(hruids)
+            ? hruids.map(String)
+            : [String(hruids)];
+    } else if (themeKey) {
+        const theme = themes.find((t) => {
+            return t.title === themeKey;
+        });
+        if (theme) {
+            hruidList = theme.hruids;
+        } else {
+            throw new NotFoundException(`Theme "${themeKey}" not found.`);
+        }
+    } else if (searchQuery) {
+        const searchResults = await learningPathService.searchLearningPaths(
+            searchQuery,
+            language
+        );
+        res.json(searchResults);
+        return;
+    } else {
+        hruidList = themes.flatMap((theme) => {
+            return theme.hruids;
+        });
+    }
+
+    const learningPaths = await learningPathService.fetchLearningPaths(
+        hruidList,
+        language,
+        `HRUIDs: ${hruidList.join(', ')}`
+    );
+    res.json(learningPaths.data);
+}