chore: Aktualisierung der Codebasis und Verbesserung der Struktur für bessere Wartbarkeit

models.py

@@ -359,4 +359,33 @@ class ForumPost(db.Model):
     replies = db.relationship('ForumPost', backref=db.backref('parent', remote_side=[id]), lazy=True)
     
     def __repr__(self):
-        return f'<ForumPost {self.title}>' 
+        return f'<ForumPost {self.title}>'
+
+# Berechtigungstypen für Mindmap-Freigaben
+class PermissionType(Enum):
+    READ = "Nur-Lesen"
+    EDIT = "Bearbeiten"
+    ADMIN = "Administrator"
+
+# Freigabemodell für Mindmaps
+class MindmapShare(db.Model):
+    """Speichert Informationen über freigegebene Mindmaps und Berechtigungen"""
+    id = db.Column(db.Integer, primary_key=True)
+    mindmap_id = db.Column(db.Integer, db.ForeignKey('user_mindmap.id'), nullable=False)
+    shared_by_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
+    shared_with_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
+    permission_type = db.Column(db.Enum(PermissionType), nullable=False, default=PermissionType.READ)
+    created_at = db.Column(db.DateTime, default=datetime.utcnow)
+    last_accessed = db.Column(db.DateTime, nullable=True)
+    
+    # Beziehungen
+    mindmap = db.relationship('UserMindmap', backref=db.backref('shares', lazy='dynamic'))
+    shared_by = db.relationship('User', foreign_keys=[shared_by_id], backref=db.backref('shared_mindmaps', lazy='dynamic'))
+    shared_with = db.relationship('User', foreign_keys=[shared_with_id], backref=db.backref('accessible_mindmaps', lazy='dynamic'))
+    
+    __table_args__ = (
+        db.UniqueConstraint('mindmap_id', 'shared_with_id', name='unique_mindmap_share'),
+    )
+    
+    def __repr__(self):
+        return f'<MindmapShare: {self.mindmap_id} - {self.shared_with_id} - {self.permission_type.name}>'