Create a Data Helper in Python for gRPC-style APIs

import json
from dataclasses import dataclass, asdict
from typing import Dict, Any


@dataclass
class User:
    user_id: int
    name: str
    email: str


class DataHelper:
    """Simple helper to demonstrate gRPC-like data handling for beginners."""

    def __init__(self) -> None:
        self._users: Dict[int, User] = {}

    def create_user(self, user: User) -> User:
        """Simulates a gRPC CreateUser request."""
        self._users[user.user_id] = user
        return user

    def get_user(self, user_id: int) -> User | None:
        """Simulates a gRPC GetUser request."""
        return self._users.get(user_id)

    def list_users(self) -> list[User]:
        """Simulates a gRPC ListUsers request."""
        return list(self._users.values())

    def to_json(self, user: User) -> str:
        """Serialize user to JSON (like protobuf-marshaling)."""
        return json.dumps(asdict(user), indent=2)


if __name__ == "__main__":
    helper = DataHelper()

    # Simulate client requests
    alice = helper.create_user(User(user_id=1, name="Alice", email="alice@example.com"))
    bob = helper.create_user(User(user_id=2, name="Bob", email="bob@example.com"))

    print("Created:", helper.to_json(alice))
    print("Fetched:", helper.to_json(helper.get_user(1)))
    print("All users:")
    for user in helper.list_users():
        print(" ", user)

    # Show request/response flow
    print("\n-- gRPC-like round trip --")
    response = helper.get_user(2)
    print("Request: GetUser(user_id=2)")
    print("Response:", helper.to_json(response) if response else "NOT FOUND")