Design a Payment Processor

Hard

+300 XP

PRO

Low Level DesignLLDSystem DesignOOPStrategy PatternState PatternCommand PatternIdempotencyRetry Logic

Design a payment processor system with multiple payment methods, transaction state management, idempotency, and retry logic.

New Transaction

Amount (USD)

Payment Strategy

Idempotency Key

Prevents double-charging if retried with same key.

System Status

Simulate Flaky Network

Transaction Ledger

Total Processed: 2

TXN-001(key_123)

$120.00•10:00:05

COMPLETED

TXN-002(key_456)

$49.99•10:15:20

Insufficient Funds

FAILED

What You'll Build

The system should support multiple payment methods including credit cards, PayPal, and bank transfers, with the ability to easily add new payment methods.
Each transaction must have a state (PENDING, PROCESSING, COMPLETED, FAILED, REFUNDED) and transition between states appropriately.
The system must ensure idempotency - processing the same payment request multiple times should not result in duplicate charges. Each transaction must have a unique idempotency key.
The system should implement retry logic for transient failures, automatically retrying failed transactions with exponential backoff up to a maximum number of attempts.
The system must handle concurrent transactions safely, ensuring thread safety and preventing race conditions.
...and more

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Step-by-Step Guidance

Follow our systematic 8-step approach to design the system from scratch. Learn how to identify actors, assign responsibilities, and create class diagrams.

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Interactive UML Builder

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Multi-Language Support

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Design Patterns

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Complete Solutions

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