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/interfaces/learningContent.ts

@@ -0,0 +1,98 @@
+export interface Transition {
+    default: boolean;
+    _id: string;
+    next: {
+        _id: string;
+        hruid: string;
+        version: number;
+        language: string;
+    };
+}
+
+export interface LearningObjectNode {
+    _id: string;
+    learningobject_hruid: string;
+    version: number;
+    language: string;
+    start_node?: boolean;
+    transitions: Transition[];
+    created_at: string;
+    updatedAt: string;
+}
+
+export interface LearningContent {
+    _id: string;
+    language: string;
+    hruid: string;
+    title: string;
+    description: string;
+    image?: string; // Image might be missing, so it's optional
+    num_nodes: number;
+    num_nodes_left: number;
+    nodes: LearningObjectNode[];
+    keywords: string;
+    target_ages: number[];
+    min_age: number;
+    max_age: number;
+    __order: number;
+}
+
+export interface EducationalGoal {
+    source: string;
+    id: string;
+}
+
+export interface ReturnValue {
+    callback_url: string;
+    callback_schema: Record<string, any>;
+}
+
+export interface LearningObjectMetadata {
+    _id: string;
+    uuid: string;
+    hruid: string;
+    version: number;
+    language: string;
+    title: string;
+    description: string;
+    difficulty: number;
+    estimated_time: number;
+    available: boolean;
+    teacher_exclusive: boolean;
+    educational_goals: EducationalGoal[];
+    keywords: string[];
+    target_ages: number[];
+    content_type: string; // Markdown, image, etc.
+    content_location?: string;
+    skos_concepts?: string[];
+    return_value?: ReturnValue;
+}
+
+export interface FilteredLearningObject {
+    key: string;
+    _id: string;
+    uuid: string;
+    version: number;
+    title: string;
+    htmlUrl: string;
+    language: string;
+    difficulty: number;
+    estimatedTime: number;
+    available: boolean;
+    teacherExclusive: boolean;
+    educationalGoals: EducationalGoal[];
+    keywords: string[];
+    description: string;
+    targetAges: number[];
+    contentType: string;
+    contentLocation?: string;
+    skosConcepts?: string[];
+    returnValue?: ReturnValue;
+}
+
+export interface LearningPathResponse {
+    success: boolean;
+    source: string;
+    data: LearningContent[] | null;
+    message?: string;
+}