How to Build a Microservice Helper in Python

import json
from typing import Any, Dict, List


class DataValidator:
    """Simple validator for common data patterns."""

    @staticmethod
    def is_valid_email(value: str) -> bool:
        """Check if value looks like an email."""
        return "@" in value and "." in value.split("@")[-1]

    @staticmethod
    def is_positive_integer(value: Any) -> bool:
        """Check if value is a positive integer."""
        return isinstance(value, int) and value > 0


class ServiceResponse:
    """Normalize service responses for downstream consumers."""

    def __init__(self, success: bool, data: Any = None, error: str = None):
        self.success = success
        self.data = data
        self.error = error

    def to_dict(self) -> Dict[str, Any]:
        """Convert response to a serializable dictionary."""
        return {
            "success": self.success,
            "data": self.data,
            "error": self.error,
        }

    def to_json(self) -> str:
        """Serialize response to JSON string."""
        return json.dumps(self.to_dict())


class UserService:
    """Simulated microservice for user operations."""

    def __init__(self):
        self._users: List[Dict[str, Any]] = []

    def create_user(self, email: str, age: int) -> ServiceResponse:
        """Create a new user with validation."""
        if not DataValidator.is_valid_email(email):
            return ServiceResponse(success=False, error="Invalid email format")
        if not DataValidator.is_positive_integer(age):
            return ServiceResponse(success=False, error="Age must be a positive integer")

        user = {"id": len(self._users) + 1, "email": email, "age": age}
        self._users.append(user)
        return ServiceResponse(success=True, data=user)

    def get_user(self, user_id: int) -> ServiceResponse:
        """Fetch a user by ID."""
        for user in self._users:
            if user["id"] == user_id:
                return ServiceResponse(success=True, data=user)
        return ServiceResponse(success=False, error=f"User {user_id} not found")


if __name__ == "__main__":
    service = UserService()

    # Create users
    response1 = service.create_user("alice@example.com", 25)
    response2 = service.create_user("bob@example.com", -5)  # Invalid age
    response3 = service.create_user("invalid-email", 30)    # Invalid email

    # Fetch a user
    response4 = service.get_user(1)
    response5 = service.get_user(99)  # Not found

    # Print all responses as JSON
    for response in [response1, response2, response3, response4, response5]:
        print(response.to_json())