import javax.swing.JOptionPane;	// for showInputDialog

/**
 *  A class to represent a "payment calculator" which computes the "equal 
 *  monthly payment amount" for a fixed-rate loan based on the amount borrowed, 
 *  the annual interest rate, and the number of years in which the loan will be
 *  repaid..
 */
public class PaymentCalculator {
    // instance vars

    int principal;     // the amount borrowed
    double rate;       // annual interest rate, as a percent
    int years;         // term of loan in years

    /**
     * Create a payment calculator object.
     * @param amount the principal (amount borrowed)
     * @param interestRate the annual rate of interest, as a per cent (APR)
     * @param term the number of years to repay the loan
     */
    public PaymentCalculator(int amount, double interestRate, int term)
    {
        principal = amount;
        rate = interestRate;
        years = term;
    }

    /**
     * Computes and returns the equal monthly payment amount on a loan
     *
     *                                            -N
     * uses formula:  Payment = AR / ( 1 - (1 + R)   )
     *
     *     where   A is principal (amount borrowed),
     *             R is MONTHLY interest rate, as a DECIMAL
     *             N is term of loan in MONTHS.
     *
     * @return the equal monthly payment amount
     */
    public double computeMonthlyPayment()
    {
        int months = years * 12;    // convert years to months

        // convert rate from annual percent to monthly decimal
        // (divide by 12 for monthly, by 100 for decimal)
        double mRate = rate / 1200;

        // TO DO: in the following statement, use the formula given above to
        // compute the "equal monthly payment" amount and assign it to
        // variable "payment," instead of 0.0.  

        double payment = 0.0 ;

        return payment ;
    }
    
    /**
     * Computes and returns the total amount paid over the life of the loan
     * 
     * @return the total of all the monthly payments
     */
    public double computeTotalPayments()
    {
        // get the equal monthly payment amount by calling computePayment
        double monthlyPayment = this.computeMonthlyPayment() ;
        
        // total payments = monthly payment amount * term of loan in years * 12
        double totalPayments = monthlyPayment * years * 12 ;

        return totalPayments ;
    }    

    /**
     * Return a string containing the loan data.
     * @return the principal, annual interest rate, and term, as a string.
     */
    public String toString()
    {
        String output = "\nLoan amount:\t$" + principal
                + "\nInterest rate:\t" + rate + "%"
                + "\nTerm of Loan:\t" + years + " years\n";
        return output;
    }
}	// end of PaymentCalculator class definition