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Stripe Integration & Multi-Currency Deposit Refactor

🏁 Overview

We integrated Stripe as a payment provider for deposits, refactored our multi-currency deposit flow, and improved our exchange rate caching logic. This ensures robust, auditable, and correct handling of all deposit scenarios, including cross-currency and zero-decimal currencies.

🛠️ What We Did

🏦 Stripe Payment Provider Integration

  • 🚀 Implemented a PaymentProvider interface and a concrete Stripe implementation using the official stripe-go SDK.
  • 🔄 Migrated to the new stripe.Client pattern for future-proofing and better testability.
  • 🧩 Injected the payment provider into the handler chain for clean separation of concerns.

🔗 Deposit Flow Refactor

  • 🏗️ The service layer now only emits a deposit event; all business logic is handled in the handler chain.
  • ➕ Added a PaymentProviderHandler to the chain, which:
  • 💳 Initiates payments with Stripe.
  • 🆔 Handles payment IDs and errors.
  • 💱 Ensured currency conversion is always performed before crediting the account, using up-to-date exchange rates.

💱 Multi-Currency & Zero-Decimal Currency Handling

  • 🐞 Fixed a critical bug: previously, JPY deposits were multiplied by 100, resulting in 100x overcharging on Stripe.
  • 🧮 Now, the amount sent to Stripe is calculated using currency metadata (e.g., decimals for USD vs. JPY).
  • 📊 All deposit and conversion logic is fully auditable and testable.

🗃️ Exchange Rate Cache Logic

  • 🔄 Refactored cache lookup to always check both direct and reverse currency pairs, with consistent TTL/freshness logic.
  • 🧹 Removed backend-specific logic for more predictable and maintainable caching.

🐞 Problems We Faced & Solutions

💱 Currency Conversion Mismatches

  • ❌ Problem: Deposits in a currency different from the account’s currency were not being converted, leading to accounting errors.
  • ✅ Solution: Enforced conversion in the handler chain, always crediting the account in its own currency.

💸 Stripe Amount Calculation for Zero-Decimal Currencies

  • ❌ Problem: JPY and other zero-decimal currencies were incorrectly multiplied by 100, causing 100x overcharging.
  • ✅ Solution: Used currency metadata to determine the correct multiplier for Stripe’s smallest unit.

🗃️ Inconsistent Exchange Rate Caching

  • ❌ Problem: Cache logic was inconsistent, sometimes missing valid rates or using stale data.
  • ✅ Solution: Unified cache lookup logic for both direct and reverse pairs, backend-agnostic.

🧩 Clean Architecture & Testability

  • ❌ Problem: Payment provider logic was mixed into the service layer, making it hard to test and extend.
  • ✅ Solution: Moved all provider logic into a dedicated handler in the chain, improving modularity and testability.

🔮 Next Steps

  • 🔔 Integrate and test Stripe sandbox webhooks for real-time payment status updates.
  • 📚 Document webhook event handling and reconciliation logic.
  • 🧪 Continue to add tests and monitoring for all payment and currency flows.

📚 References

  • stripe-go SDK
  • Stripe API Docs
  • Project code: infra/provider/stripe_payment_provider.go, pkg/handler/, pkg/service/account/, infra/provider/exchange_rates.go