In The Accountant (2016), one of the most striking moments centers on Christian Wolff, portrayed by Ben Affleck, working alone in a quiet conference room piled high with financial records 📊. The company suspects millions have vanished, yet no one has been able to trace where the money went. With intense focus, Wolff methodically dissects the ledgers. Numbers begin to cover whiteboards and walls as he follows each transaction with surgical precision. What first appears to be random disorder grad

System Design: Building a Bulletproof Payment Gateway! 🚀 Basic payment setups fail during network timeouts. To block catastrophic duplicate charges, enforce client-generated idempotency keys (UUIDs). The server saves this key first; if a duplicate request arrives, it immediately returns the cached result instead of re-charging the buyer. Never overwrite database rows to update payment statuses. Instead, implement an immutable ledger where every state change—authorized, captured, or refunded—cre