This is a simple payment engine that processes transactions for clients, including deposits, withdrawals, disputes, chargebacks, and resolutions. To run the engine:

cargo run -- transactions.csv

By default, the engine will not log rejected transactions. To enable verbose logging to stderr, which includes details about rejected transactions, use the --verbose flag:

cargo run -- transactions.csv --verbose

• Input data is in corrent format, but we still need to vigilant about invalid IDs and amounts.

• Disputes:

  • Disputes can only be filed against deposit transactions.
  • Disputes can be filed multiple times for the same deposit transaction.
  • Only 1 dispute can be active for a given deposit transaction at any time.
  • Dispute cannot be filed if the available balance is less than the disputed amount.

• Chargebacks:

  • Chargebacks can be filed without opening a dispute.
  • If a chargeback is filed without a dispute, we lock the account without changing the holds and available amounts.

• Error Handling:

  • The engine should detect and reject invalid transactions, but continue processing subsequent transactions.

• Added a CheckedDecimal type to handle decimal arithmetic with additional checks for overflow and underflow. It's backed by the rust_decimal crate.
• A custom error type is defined to try to provide meaningful error messages for various transaction failures when verbose logging is enabled.
• Separated the type to represent a CSV record (CsvInputRecord) from the type that represents a transaction (EngineTransaction) in the engine, the reasons being:
  • The engine can handle transactions in a way that is independent of the CSV format.
  • We can validate the semantic correctness of the CSV input using EngineTransaction::parse_csv_record before processing it. (e.g. Amount cannot be negative)
  • We can utlize the Rust type system to ensure that the transaction types are correct and consistent throughout the engine.
• Transactions are processed atomically, if one of the state changes fails (e.g. invalid amount causes a overflow), all changes are rolled back.

Basic unit tests are included to cover the main functionalities of the payment engine. To run the tests, use:

cargo test