Calculate transaction fees from CSV records

You are given a CSV-like multi-line string representing transactions with columns: `id,reference,amount,currency,date,merchant_id,buyer_country,transaction_type,payment_provider,status` You must compute and print fee lines in the format: `id, transaction_type, payment_provider, fee` with one output line per input row (excluding header), preserving order. ## Part 1 — Provider-based fee You are given a map `provider_fee_rules` describing how to compute a fee for each `payment_provider`. Rules: - If `status` is not a successful status (e.g., `payment_failed`), fee is `0`. - Otherwise fee is computed based on the provider’s rule (e.g., percentage + fixed, or tiered). The exact rule structure will be provided in the interview. ## Part 2 — Support multiple transaction types Extend Part 1 so that fee may depend on both `transaction_type` and `payment_provider`. ## Part 3 — Country-based fee schedule with volume discounts You are given: - A map `country_fee_rules[buyer_country] -> fee rule` (may override/extend provider rules). - A threshold `T` (number of successful transactions) after which a merchant receives a discount. - A discount definition (e.g., reduce percentage by X, or apply multiplier `d < 1`). Requirements: - Discounts are computed **per merchant** (`merchant_id`) based on that merchant’s cumulative successful transaction count (or volume) up to the current transaction. - Output the computed fee for each row. ## Notes - Specify how you parse `amount` (integer smallest unit) and how you round fees. - Aim for an efficient single pass over the rows while maintaining per-merchant aggregates.