add delete user mutation

app/schema/mutations/__init__.py

@@ -4,3 +4,4 @@ from .delete_todo import DeleteTodo
 from .update_todo import UpdateTodo
 from .create_user import CreateUser
 from .update_user import UpdateUser
+from .delete_user import DeleteUser

app/schema/mutations/delete_user.py

@@ -0,0 +1,20 @@
+import graphene
+
+from app.schema.types.user import UserResponseField
+from app.usecases.user.delete_user import delete_user
+
+
+class DeleteUser(graphene.Mutation):
+    class Arguments:
+        user_id = graphene.String(required=True)
+
+    result = graphene.Field(UserResponseField)
+
+    def mutate(self, info, user_id: str):
+        user, is_success = delete_user(user_id)
+        error_message = "This user does not exist." if not is_success else None
+        return DeleteUser(
+            UserResponseField(
+                user=user, is_success=is_success, error_message=error_message
+            )
+        )

app/schema/mutations/mutations.py

@@ -1,6 +1,14 @@
 import graphene
 
-from . import CreateTodo, DeleteTodo, UpdateTodo, CloseTodo, CreateUser, UpdateUser
+from . import (
+    CreateTodo,
+    DeleteTodo,
+    UpdateTodo,
+    CloseTodo,
+    CreateUser,
+    UpdateUser,
+    DeleteUser,
+)
 
 
 class Mutations(graphene.ObjectType):
@@ -12,3 +20,4 @@ class Mutations(graphene.ObjectType):
     # user
     create_user = CreateUser.Field()
     update_user = UpdateUser.Field()
+    delete_user = DeleteUser.Field()

app/usecases/user/delete_user.py

@@ -0,0 +1,11 @@
+from typing import Tuple
+
+from app.models.user import User
+from app.repositories.users import user_exists, remove_user
+
+
+def delete_user(user_id: str) -> Tuple[User, bool]:
+    if not user_exists(user_id):
+        return None, False
+
+    return remove_user(user_id), True