34.DesignaLoyaltyProgram.py

# Design a simple Loyalty Program system where users can enroll, earn points from purchases, 
# and redeem points for rewards. The system must run fully in-memory, 
# support thread-safe operations, and allow customizable point-calculation strategies.

import threading
import time

class PointStrategy:
    def calculate(self, amount):
        raise NotImplementedError
    
class DefaultPointStrategy(PointStrategy):
    def calculate(self, amount):
        return amount // 10
    
class User:
    def __init__(self, user_id, name):
        self.user_id = user_id
        self.name = name
        self.points = 0

    def add_points(self, p):
        self.points += p

    def deduct_points(self, p):
        if self.points >= p:
            self.points -= p
            return True
        return False
    
class LoyaltyService:
    _instance = None
    _lock = threading.Lock()

    def __new__(cls):
        if not cls._instance:
            cls._instance = super(LoyaltyService, cls).__new__(cls)
        return cls._instance
    
    def __init__(self):
        self.users = {}
        self.transactions = []
        self.lock = threading.Lock()
        self.strategy = DefaultPointStrategy()

    def enroll_user(self, user_id, name):
        self.users[user_id] = User(user_id, name)

    def earn_points(self, user_id, amount):
        pts = self.strategy.calculate(amount)

        with self.lock:
            user = self.users[user_id]
            user.add_points(pts)
            self.transactions.append(
                ("earn", user_id, pts, time.time())
            )
        return pts
    
    def redeem_points(self, user_id, pts_required):
        with self.lock:
            user = self.users[user_id]
            if user.deduct_points(pts_required):
                self.transactions.append(
                    ("redeem", user_id, pts_required, time.time())
                )
                return True
            return False
        
    def get_user_points(self, user_id):
        return self.users[user_id].points
    
if __name__ == "__main__":

    service = LoyaltyService()            # Create (or fetch) Singleton instance

    service.enroll_user("U1", "Bharadwaj")  # Register a new user

    earned = service.earn_points("U1", 250)  # Earn points for spending amount
    print("Points earned:", earned)          # Expected: 25

    redeemed = service.redeem_points("U1", 10)  # Redeem a portion of points
    print("Redeemed:", redeemed)                # Expected: True

    print("Current Points:", service.get_user_points("U1"))  # Expected: 15