Requirements

Functional Requirements:

• Ability to send money to someone through different method (wire, credit/debit card, etc)
• Account management
  • See current account status (how much money)
  • See transaction history
  • Ability to manage recipient
• Multi-currency support with clear fees, rate conversion mechanisms
• Buyers
  • Ability to request a refund (reason required, like item not received or not matching description)
• Seller
  • Ability to dispute a refund request

Non-Functional Requirements:

• Scalable: in order to handle many payment worldwide
• Secure:
  • personal informations from buyers/sellers must remain confidential
  • transaction must no be tempered with
• latency: transaction should be concluded fast (buyers should not wait)
• availability: available 24/24h 7/7j

API Design

• sendMoney(buyerId, sellerId, amount, buyerCurrency, paymentMethod, offerId)
  • description: Ability to send money from a buyer to a seller for a specific offer and amount, through a provided method)
  • returns:
    • a transaction identifier
    • in case of synchronous transaction processing the status may be returned, in case of asynchronous processing an additional endpoint would be required to fetch the transaction status
• accountStatus(userId)
  • Description: Display account information, namely how much money for a specific user
  • returns:
    • amountOfmoney
    • currency
    • userInformation
• transactionHistory(userId)
  • Description: display transaction history for a specific user
  • Returns:
    • list of transaction, may be already processed, in progress, or under refund request/dispute

Other APIs to consider later:

• addRecipient(userId, recipientName, recipientMetadata)
  • Description: Ability to a recipient for a specific user, with a recipient name for clarity. recipientMetadata will contain information such as method (wire, credit/debit card, etc) and additional data like account number for a wire, card number, etc
  • Returns:
    • recipientId
• findConversionRateAndFees(originalAmount, originalCurrency, targetCurrency)
  • Description: Find the conversion rate and fees applied to an amount based on the original and target currency, as well as the amount (likely more useful for fee calculation)
  • Returns:
    • Conversion rate between original and target currency.
    • Transaction fees in case the transaction is actually made
• requestRefund(userId, offerId, reason)
  • Description: Buyer can request a refund for a specific offer. A reason must be provided
  • Returns:
    • requestRefundId
• disputeRefundRequest(userId, refundRequestId)
  • Description: Seller can dispute a refund request. Status of the refund request will be updated to something like "disputed" to underline in progress dispute process
  • Returns:
    • Success

High-Level Design

See "High level diagram"

Detailed Component Design

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.