package financial

import "math"

// NPVCalculatorImpl implements NPVCalculator interface
type NPVCalculatorImpl struct{}

// NewNPVCalculator creates a new NPV calculator
func NewNPVCalculator() NPVCalculator {
	return &NPVCalculatorImpl{}
}

// CalculateNPV calculates Net Present Value
// NPV = -CAPEX + Σ(cash_flow / (1 + r)^t) for t=1 to n
func (npv *NPVCalculatorImpl) CalculateNPV(capex, annualCashFlow, discountRate float64, years int) float64 {
	npvValue := -capex // Initial investment (negative)

	for year := 1; year <= years; year++ {
		discountFactor := math.Pow(1+discountRate, float64(year))
		npvValue += annualCashFlow / discountFactor
	}

	return npvValue
}