package payment import ( "github.com/shopspring/decimal" ) // CalculatePayAmount computes the total pay amount given a recharge amount and // fee rate (percentage). Fee = amount * feeRate / 100, rounded UP (away from zero) // to 2 decimal places. The returned string is formatted to exactly 2 decimal places. // If feeRate <= 0, the amount is returned as-is (formatted to 2 decimal places). func CalculatePayAmount(rechargeAmount float64, feeRate float64) string { amount := decimal.NewFromFloat(rechargeAmount) if feeRate <= 0 { return amount.StringFixed(2) } rate := decimal.NewFromFloat(feeRate) fee := amount.Mul(rate).Div(decimal.NewFromInt(100)).RoundUp(2) return amount.Add(fee).StringFixed(2) }