package ledger

import "errors"

// ErrShortBalance is returned when a posting would drive the balance negative.
var ErrShortBalance = errors.New("ledger: insufficient balance")

// Apply posts one delta against the running balance and returns the new total.
func Apply(balance, delta int64) (int64, error) {
	if balance+delta < 0 {
		return balance, ErrShortBalance
	}
	return balance + delta, nil
}