implement endpoints for list, create & remove of notification methods; move owner check of notification method into own file

api/src/lib/check-notification-method-owner.ts

@@ -0,0 +1,30 @@
+import { getDbContext, getDbEnv } from '../db/client'
+import { notificationMethod } from '../db/schema';
+import { NotificationMethodSelect } from '../types/notification-method'
+import { DatabaseError, InvalidParameter } from '../errors'
+import { eq } from 'drizzle-orm';
+
+type NotificationMethodUser = Pick<NotificationMethodSelect, "userId">;
+
+/**
+ * Checks if a specified user is the owner of a notification method and returns the owner if valid
+ * @param db DB connection (already defined as variable/const)
+ * @param methodId notificationMethodId to check
+ * @param userId User to check wheter it is the owner
+ * @returns Object with the owners userId
+ */
+export async function getNotificationMethodOwner(db: ReturnType<typeof getDbContext | typeof getDbEnv>, methodId: number, userId: number): Promise<NotificationMethodUser>{
+    try{
+        const method = await db.select({
+            userId: notificationMethod.userId
+        }).from(notificationMethod)
+        .where(eq(notificationMethod.id, methodId)).get();
+        
+        if(!method || method.userId !== userId) throw new InvalidParameter('notificationMethodId');
+        else return method;
+    }
+    catch(e){
+        if(e instanceof InvalidParameter) throw e;
+        throw new DatabaseError();
+    }
+}