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.