Constructor

• supportedPaymentMethods contains the allowed payment methods such as "CARD", "UPI", "WALLET".
• All payment methods will contain only A-Z and '_'
• Duplicate payment methods, if any, should be treated as one supported method.

Exact Method Signatures

Create Order

• Creates a new order with initial status CREATED.
• On creation, PAYMENT_METHOD is NONE, PAYMENT_REF is NONE, REFUND_REQUIRED is false, and CANCEL_REASON is NONE.
• Return checks must be evaluated in this exact order:
• If orderId already exists, return "ORDER_ALREADY_EXISTS".
• Else if totalAmount <= 0, return "INVALID_AMOUNT".
• Else create the order and return "ORDER_CREATED".

Start Payment

• Starts payment for an existing order using the given payment method.
• Allowed only when the current order status is CREATED or PAYMENT_FAILED.
• At most one active payment flow can exist per order.
• If this method returns "PAYMENT_STARTED", the order status becomes PAYMENT_IN_PROGRESS, PAYMENT_METHOD becomes the given method, and PAYMENT_REF becomes NONE.
• Return checks must be evaluated in this exact order:
• If the order does not exist, return "ORDER_NOT_FOUND".
• Else if the method is not supported, return "UNSUPPORTED_PAYMENT_METHOD".
• Else if payment cannot be started from the current state, return "ORDER_NOT_PAYABLE".
• Else start payment and return "PAYMENT_STARTED".

Complete Payment

• Completes the current active payment flow for the order.
• Allowed only when the current order status is PAYMENT_IN_PROGRESS.
• Return checks must be evaluated in this exact order:
• If the order does not exist, return "ORDER_NOT_FOUND".
• Else if there is no active payment flow for that order, return "PAYMENT_NOT_IN_PROGRESS".
• Else if paymentSucceeded is true, the order status becomes PAID, PAYMENT_REF becomes paymentReference, and the method returns "PAYMENT_COMPLETED".
• Else the order status becomes PAYMENT_FAILED, PAYMENT_REF becomes NONE, and the method returns "PAYMENT_FAILED".
• When payment fails, PAYMENT_METHOD remains the method from the latest startPayment call that returned "PAYMENT_STARTED".

Cancel Order

• Return checks must be evaluated in this exact order:
• If the order does not exist, return "ORDER_NOT_FOUND".
• Else if the current status is already CANCELLED or CANCELLED_REFUND_DUE, return "ORDER_ALREADY_CANCELLED".
• Else if the current status is PAID, the new status becomes CANCELLED_REFUND_DUE, REFUND_REQUIRED becomes true, CANCEL_REASON becomes reason, and the method returns "ORDER_CANCELLED_WITH_REFUND".
• Else if the current status is CREATED, PAYMENT_IN_PROGRESS, or PAYMENT_FAILED, the new status becomes CANCELLED, REFUND_REQUIRED remains false, CANCEL_REASON becomes reason, and the method returns "ORDER_CANCELLED".
• Cancellation does not change PAYMENT_METHOD.
• Cancellation does not change PAYMENT_REF. Therefore it stays NONE if payment was never successfully completed, and it keeps the successful payment reference if payment had already completed successfully.

Get Order Details

• Returns the current order details in the exact format shown below.
• If the order exists, return a List<String> with exactly these lines in this order:
  • "ORDER:<orderId>"
  • "AMOUNT:<totalAmount>"
  • "STATUS:<status>"
  • "PAYMENT_METHOD:<paymentMethod or NONE>"
  • "PAYMENT_REF:<paymentReference or NONE>"
  • "REFUND_REQUIRED:<true or false>"
  • "CANCEL_REASON:<reason or NONE>"
• If the order does not exist, return List<String> containing only "ORDER_NOT_FOUND".

Order States

• CREATED — order exists but payment has not started.
• PAYMENT_IN_PROGRESS — payment has been started and is awaiting completion.
• PAID — payment completed successfully.
• PAYMENT_FAILED — the last payment attempt failed.
• CANCELLED — order was cancelled before successful payment.
• CANCELLED_REFUND_DUE — order was cancelled after successful payment, so refund is required.

Behavior Rules

• All operations must be deterministic and in-memory.
• An order id is unique across the system.
• The latest startPayment call that returns "PAYMENT_STARTED" decides the active payment method for the next completePayment call.
• After a failed payment, payment may be started again using any supported payment method.
• After an order reaches CANCELLED or CANCELLED_REFUND_DUE, no further payment operations are allowed.
• Use exact return strings and exact output formatting for getOrderDetails.
• Actual refund processing is out of scope for this problem. This problem only tracks whether a refund is required.
• All string inputs passed to methods satisfy the stated length constraints.

Constraints

• 1 ≤ supportedPaymentMethods.size() ≤ 20
• 1 ≤ orderId.length() ≤ 50
• 1 ≤ paymentMethod.length() ≤ 30
• 1 ≤ paymentReference.length() ≤ 50
• 1 ≤ reason.length() ≤ 100
• 1 ≤ totalAmount ≤ 10^9
• At most 10^4 total method calls will be made.

Examples

Example 1

Example 2

Example 3

Example 4

Example 5

Example 6