✨(backend) add server-to-server API endpoint to create documents

We want trusted external applications to be able to create documents
via the API on behalf of any user. The user may or may not pre-exist
in our database and should be notified of the document creation by
email.

src/backend/core/api/serializers.py

@@ -4,6 +4,7 @@ import mimetypes
 
 from django.conf import settings
 from django.db.models import Q
+from django.utils.functional import lazy
 from django.utils.translation import gettext_lazy as _
 
 import magic
@@ -11,6 +12,10 @@ from rest_framework import exceptions, serializers
 
 from core import enums, models
 from core.services.ai_services import AI_ACTIONS
+from core.services.converter_services import (
+    ConversionError,
+    YdocConverter,
+)
 
 
 class UserSerializer(serializers.ModelSerializer):
@@ -227,6 +232,96 @@ class DocumentSerializer(ListDocumentSerializer):
         return value
 
 
+class ServerCreateDocumentSerializer(serializers.Serializer):
+    """
+    Serializer for creating a document from a server-to-server request.
+
+    Expects 'content' as a markdown string, which is converted to our internal format
+    via a Node.js microservice. The conversion is handled automatically, so third parties
+    only need to provide markdown.
+
+    Both "sub" and "email" are required because the external app calling doesn't know
+    if the user will pre-exist in Docs database. If the user pre-exist, we will ignore the
+    submitted "email" field and use the email address set on the user account in our database
+    """
+
+    # Document
+    title = serializers.CharField(required=True)
+    content = serializers.CharField(required=True)
+    # User
+    sub = serializers.CharField(
+        required=True, validators=[models.User.sub_validator], max_length=255
+    )
+    email = serializers.EmailField(required=True)
+    language = serializers.ChoiceField(
+        required=False, choices=lazy(lambda: settings.LANGUAGES, tuple)()
+    )
+    # Invitation
+    message = serializers.CharField(required=False)
+    subject = serializers.CharField(required=False)
+
+    def create(self, validated_data):
+        """Create the document and associate it with the user or send an invitation."""
+        language = validated_data.get("language", settings.LANGUAGE_CODE)
+
+        # Get the user based on the sub (unique identifier)
+        try:
+            user = models.User.objects.get(sub=validated_data["sub"])
+        except (models.User.DoesNotExist, KeyError):
+            user = None
+            email = validated_data["email"]
+        else:
+            email = user.email
+            language = user.language or language
+
+        try:
+            converter_response = YdocConverter().convert_markdown(
+                validated_data["content"]
+            )
+        except ConversionError as err:
+            raise exceptions.APIException(detail="could not convert content") from err
+
+        document = models.Document.objects.create(
+            title=validated_data["title"],
+            content=converter_response["content"],
+            creator=user,
+        )
+
+        if user:
+            # Associate the document with the pre-existing user
+            models.DocumentAccess.objects.create(
+                document=document,
+                role=models.RoleChoices.OWNER,
+                user=user,
+            )
+        else:
+            # The user doesn't exist in our database: we need to invite him/her
+            models.Invitation.objects.create(
+                document=document,
+                email=email,
+                role=models.RoleChoices.OWNER,
+            )
+
+        # Notify the user about the newly created document
+        subject = validated_data.get("subject") or _(
+            "A new document was created on your behalf!"
+        )
+        context = {
+            "message": validated_data.get("message")
+            or _("You have been granted ownership of a new document:"),
+            "title": subject,
+        }
+        document.send_email(subject, [email], context, language)
+
+        return document
+
+    def update(self, instance, validated_data):
+        """
+        This serializer does not support updates.
+        """
+        raise NotImplementedError("Update is not supported for this serializer.")
+
+
 class LinkDocumentSerializer(BaseResourceSerializer):
     """
     Serialize link configuration for documents.