Payment Gateway Rules

• Every payment gateway has a unique, case-sensitive name.
• A newly registered gateway is enabled by default.
• Each gateway supports a list of currencies.
• An empty currency list means that the gateway supports every currency.
• Disabled gateways cannot process new payments.

Gateway Selection

• If the preferred gateway is enabled and supports the transaction currency, use it.
• Otherwise, use the lexicographically smallest enabled gateway that supports the currency.
• An empty preferred gateway name means that no gateway is preferred.
• If no eligible gateway exists, the payment fails.

Credit Card Rules

• A valid card number contains only digits.
• Its length must be between 12 and 19 characters, inclusive.
• No Luhn checksum or card-network validation is required.
• The full card number must never appear in a returned value.

Transaction Rules

• Every transaction ID is case-sensitive.
• The first call using a transaction ID creates and stores its transaction result.
• Reusing a transaction ID must not create another charge and must return its currently stored result.
• When a transaction ID already exists, all other arguments supplied to processPayment are ignored, and the currently stored result is returned without validating the new arguments.
• Only a successful payment may be refunded.
• Only full refunds are supported.
• Disabling or removing access to a gateway does not change transactions that were processed earlier.

Constructor

PaymentProcessingSystem()

• Creates an empty payment processing system.

Methods

Add Payment Gateway

boolean addPaymentGateway(String gatewayName, List<String> supportedCurrencies)

• Registers an enabled payment gateway.
• Returns true when the gateway is added.
• Returns false when a gateway with the same name already exists.

Enable or Disable Payment Gateway

boolean setPaymentGatewayEnabled(String gatewayName, boolean enabled)

• Updates the enabled state of an existing gateway.
• Returns true when the gateway exists, including when it already has the requested state.
• Returns false when the gateway does not exist.

Process Payment

String processPayment(String transactionId, String cardNumber, int amountInCents, String currency, String preferredGateway)

• If the transaction ID already exists, returns its currently stored result, including "REFUNDED,gatewayName" for a refunded transaction.
• Returns "SUCCESS,gatewayName" when the payment succeeds.
• Returns "FAILED,INVALID_CARD" when the card number is invalid.
• Returns "FAILED,NO_AVAILABLE_GATEWAY" when no eligible gateway is available.
• The result is stored using the transaction ID.

Refund Payment

boolean refundPayment(String transactionId)

• Changes a successful transaction from SUCCESS to REFUNDED.
• Returns true when the refund is completed.
• Returns false when the transaction is missing, failed, or already refunded.

Get Transaction Status

String getTransactionStatus(String transactionId)

• Returns "SUCCESS,gatewayName" for a successful payment.
• Returns "REFUNDED,gatewayName" for a refunded payment.
• Returns the stored failure result for a failed payment.
• Returns "NOT_FOUND" when the transaction does not exist.

Constraints

• 1 ≤ gatewayName.length() ≤ 50
• 0 ≤ supportedCurrencies.size() ≤ 50
• Every currency is a three-character uppercase string.
• 1 ≤ transactionId.length() ≤ 100
• 1 ≤ cardNumber.length() ≤ 25
• 1 ≤ amountInCents ≤ 100,000,000
• currency.length() = 3
• preferredGateway is either an empty string or a gateway name.
• At most 100 gateways may be registered.
• At most 100,000 method calls will be made.
• No parameter value will be null.

Examples

Example 1

Example 2

Example 3