Merchant Balances After Chargebacks

Compute merchant balances from a chronological stream of payment events.

Each event is [type, merchant_id, payment_id, amount] where type is "charge", "refund", or "chargeback". Refund and chargeback events always carry the same merchant_id as the original charge. Process events in order:

• charge: the first charge for a payment_id adds amount to the merchant's balance and opens the payment with amount remaining. A repeated charge for an existing payment_id is ignored.
• refund: subtracts min(amount, remaining) from the merchant and from the payment's remaining amount. A refund larger than what is left only refunds what is left.
• chargeback: subtracts min(amount, remaining) plus a fixed dispute_fee, then closes the payment.
• A refund or chargeback for an unknown payment_id, or for a payment that is already closed, is ignored (no fee).

Return [merchant_id, balance] for every merchant whose final balance is non-zero, sorted by merchant_id. Balances may be negative.