SakuraPay

SakuraPay is a full-featured payment processing platform designed to simulate real-world financial transaction architectures, merchant settlements, currency conversions, and recurring subscription billing without mock shortcuts.

Designed the transaction state machine, double-entry ledger database schema, idempotency token validation middleware, and automated webhook delivery engine with exponential retry backoff.

Built with FastAPI, PostgreSQL, and Docker. Implemented pessimistic row-level locking to prevent race conditions and double-spending, Redis atomic primitives for distributed rate limiting, and HMAC-SHA256 signature verification for outgoing webhooks.

Provides a hardened, production-tested architecture for transaction handling, demonstrating how financial platforms achieve zero double-spending and fault-tolerant webhook distribution.