// Model redakcyjny, wersja 1, 26.09.2026. Bez danych klientów.
// P: saldo PLN; annualRate: oprocentowanie nominalne (np. 0.06); months: pozostałe raty.
// Nadpłata po naliczeniu odsetek i zapłacie raty, utrzymanie raty bazowej, krótszy okres.
// Równe miesiące, stopa stała w symulacji, brak opłat; zaokrąglenia tylko na wyjściu.
function payment(P,annualRate,months){
 if(!Number.isFinite(P)||P<=0||!Number.isFinite(annualRate)||annualRate<0||!Number.isInteger(months)||months<=0)throw Error('Invalid input');
 const r=annualRate/12;return r===0?P/months:P*r/(1-Math.pow(1+r,-months));
}
function simulate(P,annualRate,months,extra=0){
 if(!Number.isFinite(extra)||extra<0)throw Error('Invalid extra');
 const base=payment(P,annualRate,months),r=annualRate/12;
 let balance=P,interest=0,total=0,extraTotal=0,n=0;const schedule=[];
 while(balance>1e-7&&n<months+1){
  const dueInterest=balance*r,regular=Math.min(base,balance+dueInterest),additional=Math.min(extra,Math.max(0,balance+dueInterest-regular));
  const paid=regular+additional;balance=Math.max(0,balance+dueInterest-paid);
  interest+=dueInterest;total+=paid;extraTotal+=additional;n++;
  schedule.push({month:n,balance,interest:dueInterest,regular,extra:additional});
 }
 if(balance>0.01)throw Error('Unpaid balance');
 return {payment:base,months:n,interest,total,extraTotal,schedule};
}
function compare(P,years,annualRate=0.06,extra=500){
 const standard=simulate(P,annualRate,years*12),accelerated=simulate(P,annualRate,years*12,extra);
 return {principal:P,years,annualRate,extra,basePayment:standard.payment,monthlyOutlay:standard.payment+extra,baseMonths:standard.months,overpaidMonths:accelerated.months,monthsSaved:standard.months-accelerated.months,baseInterest:standard.interest,overpaidInterest:accelerated.interest,interestSaved:standard.interest-accelerated.interest,extraTotal:accelerated.extraTotal};
}
module.exports={payment,simulate,compare};