Saga Compensating Transaction Mock in Python

import random
import time


class OrderService:
    def __init__(self):
        self.orders = {}

    def create_order(self, order_id):
        print(f"[Order] Creating order {order_id}...")
        time.sleep(0.1)
        if random.random() < 0.3:  # 30% chance of failure
            raise RuntimeError(f"Order {order_id} creation failed")
        self.orders[order_id] = {"status": "pending"}
        print(f"[Order] Order {order_id} created")
        return True

    def cancel_order(self, order_id):
        print(f"[Order] Cancelling order {order_id}...")
        self.orders.pop(order_id, None)
        print(f"[Order] Order {order_id} cancelled")


class PaymentService:
    def charge(self, order_id, amount):
        print(f"[Payment] Charging ${amount} for order {order_id}...")
        time.sleep(0.1)
        if random.random() < 0.25:  # 25% chance of failure
            raise RuntimeError(f"Payment for {order_id} failed")
        print(f"[Payment] Charged ${amount} for order {order_id}")
        return True

    def refund(self, order_id, amount):
        print(f"[Payment] Refunding ${amount} for order {order_id}...")
        print(f"[Payment] Refunded ${amount} for order {order_id}")


class InventoryService:
    def reserve(self, order_id, product_id):
        print(f"[Inventory] Reserving {product_id} for order {order_id}...")
        time.sleep(0.1)
        if random.random() < 0.2:  # 20% chance of failure
            raise RuntimeError(f"Inventory reservation for {order_id} failed")
        print(f"[Inventory] Reserved {product_id} for order {order_id}")
        return True

    def release(self, order_id, product_id):
        print(f"[Inventory] Releasing {product_id} for order {order_id}...")
        print(f"[Inventory] Released {product_id} for order {order_id}")


def saga_order(order_id, amount, product_id):
    order_svc = OrderService()
    payment_svc = PaymentService()
    inventory_svc = InventoryService()

    # Step 1: Create order
    try:
        order_svc.create_order(order_id)
    except Exception as e:
        print(f"[Saga] Failed at step 1: {e}")
        return "FAILED"

    # Step 2: Charge payment
    try:
        payment_svc.charge(order_id, amount)
    except Exception as e:
        print(f"[Saga] Failed at step 2: {e}")
        # Compensate step 1
        order_svc.cancel_order(order_id)
        print("[Saga] Compensation: order cancelled")
        return "FAILED"

    # Step 3: Reserve inventory
    try:
        inventory_svc.reserve(order_id, product_id)
    except Exception as e:
        print(f"[Saga] Failed at step 3: {e}")
        # Compensate steps 1 & 2
        payment_svc.refund(order_id, amount)
        order_svc.cancel_order(order_id)
        print("[Saga] Compensation: payment refunded, order cancelled")
        return "FAILED"

    print(f"[Saga] Order {order_id} completed successfully")
    return "SUCCESS"


if __name__ == "__main__":
    random.seed(42)  # Deterministic for demo
    for i in range(5):
        result = saga_order(f"ORD-{i}", 99.99, "PROD-100")
        print(f"Saga {i} result: {result}\n")