feat: add PUT endpoint to update letters and manage associated images

backend/letters/views.py

@@ -1,5 +1,6 @@
 from rest_framework import generics
 from rest_framework.permissions import IsAuthenticated
+from rest_framework.response import Response
 
 from letters.models import Letter, LetterImage
 from letters.serializers import LetterSerializer
@@ -14,8 +15,16 @@ class LetterView(generics.ListCreateAPIView):
         """return only letters of the authenticated user"""
         return Letter.objects.filter(user=self.request.user)
 
-    def perform_create(self, serializer):
-        letter = serializer.save(user=self.request.user)
-        image_files = self.request.FILES.getlist("image_files")
-        for image_file in image_files:
+    def put(self, request, public_id):
+        serializer = self.get_serializer(data=request.data)
+        serializer.is_valid(raise_exception=True)
+
+        letter, created = Letter.objects.update_or_create(
+            public_id=public_id, user=request.user, defaults=serializer.validated_data
+        )
+
+        LetterImage.objects.filter(letter=letter).delete()
+        for image_file in request.FILES.getlist("image_files"):
             LetterImage.objects.create(letter=letter, file=image_file, file_name=image_file.name)
+
+        return Response(serializer.data, status=201 if created else 200)