Move backend source to server/ subpackage

To clarify the organization.

server/src/infra/graphql/mutation.rs

@@ -0,0 +1,55 @@
+use crate::domain::handler::{BackendHandler, CreateUserRequest};
+use juniper::{graphql_object, FieldResult, GraphQLInputObject};
+
+use super::api::Context;
+
+#[derive(PartialEq, Eq, Debug)]
+/// The top-level GraphQL mutation type.
+pub struct Mutation<Handler: BackendHandler> {
+    _phantom: std::marker::PhantomData<Box<Handler>>,
+}
+
+impl<Handler: BackendHandler> Mutation<Handler> {
+    pub fn new() -> Self {
+        Self {
+            _phantom: std::marker::PhantomData,
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Debug, GraphQLInputObject)]
+/// The details required to create a user.
+pub struct UserInput {
+    id: String,
+    email: String,
+    display_name: Option<String>,
+    first_name: Option<String>,
+    last_name: Option<String>,
+}
+
+#[graphql_object(context = Context<Handler>)]
+impl<Handler: BackendHandler + Sync> Mutation<Handler> {
+    async fn create_user(
+        context: &Context<Handler>,
+        user: UserInput,
+    ) -> FieldResult<super::query::User<Handler>> {
+        if !context.validation_result.is_admin {
+            return Err("Unauthorized user creation".into());
+        }
+        context
+            .handler
+            .create_user(CreateUserRequest {
+                user_id: user.id.clone(),
+                email: user.email,
+                display_name: user.display_name,
+                first_name: user.first_name,
+                last_name: user.last_name,
+            })
+            .await?;
+        Ok(context
+            .handler
+            .get_user_details(&user.id)
+            .await
+            .map(Into::into)?)
+    }
+}