[Multi-User]: Part 0 - Add support for logging in with Google (#487)

* Add concept of user authentication to the request session via GoogleUser

src/database/adapters/__init__.py

@@ -0,0 +1,78 @@
+from typing import Type, TypeVar
+import uuid
+
+from django.db import models
+from django.contrib.sessions.backends.db import SessionStore
+
+# Import sync_to_async from Django Channels
+from asgiref.sync import sync_to_async
+
+from fastapi import HTTPException
+
+from database.models import KhojUser, GoogleUser, NotionConfig
+
+ModelType = TypeVar("ModelType", bound=models.Model)
+
+
+async def retrieve_object(model_class: Type[ModelType], id: int) -> ModelType:
+    instance = await model_class.objects.filter(id=id).afirst()
+    if not instance:
+        raise HTTPException(status_code=404, detail=f"{model_class.__name__} not found")
+    return instance
+
+
+async def set_notion_config(token: str, user: KhojUser):
+    notion_config = await NotionConfig.objects.filter(user=user).afirst()
+    if not notion_config:
+        notion_config = await NotionConfig.objects.acreate(token=token, user=user)
+    else:
+        notion_config.token = token
+        await notion_config.asave()
+    return notion_config
+
+
+async def get_or_create_user(token: dict) -> KhojUser:
+    user = await get_user_by_token(token)
+    if not user:
+        user = await create_google_user(token)
+    return user
+
+
+async def create_google_user(token: dict) -> KhojUser:
+    user_info = token.get("userinfo")
+    user = await KhojUser.objects.acreate(
+        username=user_info.get("email"), email=user_info.get("email"), uuid=uuid.uuid4()
+    )
+    await user.asave()
+    await GoogleUser.objects.acreate(
+        sub=user_info.get("sub"),
+        azp=user_info.get("azp"),
+        email=user_info.get("email"),
+        name=user_info.get("name"),
+        given_name=user_info.get("given_name"),
+        family_name=user_info.get("family_name"),
+        picture=user_info.get("picture"),
+        locale=user_info.get("locale"),
+        user=user,
+    )
+
+    return user
+
+
+async def get_user_by_token(token: dict) -> KhojUser:
+    user_info = token.get("userinfo")
+    google_user = await GoogleUser.objects.filter(sub=user_info.get("sub")).select_related("user").afirst()
+    if not google_user:
+        return None
+    return google_user.user
+
+
+async def retrieve_user(session_id: str) -> KhojUser:
+    session = SessionStore(session_key=session_id)
+    if not await sync_to_async(session.exists)(session_key=session_id):
+        raise HTTPException(status_code=401, detail="Invalid session")
+    session_data = await sync_to_async(session.load)()
+    user = await KhojUser.objects.filter(id=session_data.get("_auth_user_id")).afirst()
+    if not user:
+        raise HTTPException(status_code=401, detail="Invalid user")
+    return user