import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
import java.util.Scanner;
import javax.swing.*;

public class mortgageCalculatorGui {

    public static void main(String[] args) {        
        //------------------------
        //Use GUI to calculate mortgages
        mcFrame mc=new mcFrame();
        mc.createWindow();
    }
}
class MortgageCalculator {
    private int years; //number of years on the loan
    private double loan;  // amount of loan
    private double interest;// percentage of interest
    private double monthlyPayment;// amount ofmonthly payment 
    private double totalPayment; // this is the loan amount plus interest
    private double interestPaid;//monthly interst payment
    private double balanceLoan;// loan balance
    private double balancePrinciple;// principle balance
    //display variables
    private String str;// header, 
    private int displayCount;//display counter
    private int scroll;//scroll counter
    private Scanner input;
    //display for gui
    private StringBuffer strForGui; //string buffer for gui display

    public MortgageCalculator(int years, double loan, double interest) {
        this.years = years;
        this.loan = loan;
        this.interest = interest;
        input = new Scanner(System.in);
        //get monthly payment
        //interest is in percentage, so for monthly interest, interest = (interset/100)/12=interest/1200..
        monthlyPayment = loan * (interest / 1200) * (1 + 1 / (Math.pow(1 + interest / 1200, years * 12) - 1));
        totalPayment = monthlyPayment * years * 12;//the total payment is the sum of loan amount and the 
        //total of the interest paid over the course of the loan
        balanceLoan = totalPayment;
        balancePrinciple = this.loan;
    }
    //use to display schedule on console
    public void displaySchedule() {
        //display schedule
        while (displayCount < years * 12) {
            //prepare the heading
            str=(String.format("%10s %10s %10s %10s", "month", "payment", "interest", "balance"));// returns the next element in the literation, 10s means reserve 10 spaces for a string variable
            System.out.println(str);
            while ((scroll + 1 < 13) && (displayCount < years * 12)) {
                interestPaid = balancePrinciple * interest / 1200; //monthly interest paid
                balanceLoan = balanceLoan - monthlyPayment; //calculated monthly loan balance
                balancePrinciple = balancePrinciple - (monthlyPayment - interestPaid);//calculated monthly principle
                str=(String.format("%10d %10.2f %10.2f %10.2f", displayCount + 1, monthlyPayment, interestPaid, balanceLoan));
                System.out.println(str);
                scroll++;
                displayCount++;
            }
            scroll = 0;
            System.out.println("Press enter to continue");
            input.nextLine();
        }
    }
    //use to display schedule on GUI
    public String displayScheduleForGui() {
        strForGui = new StringBuffer();
        DecimalFormat formatter = new DecimalFormat("$###,###.00");
        strForGui.append(String.format("%15s %15s %15s %15s\n", "month", "payment", "interest", "balance"));
        while(displayCount < years*12) {            
            interestPaid = balancePrinciple * interest / 1200; //monthly interest paid
            balanceLoan = balanceLoan - monthlyPayment; //calculated monthly loan balance
            balancePrinciple = balancePrinciple - (monthlyPayment - interestPaid);//calculated monthly principle
            strForGui.append(String.format("%15d %20s %20s %20s\n", displayCount + 1, 
                                                                    formatter.format(monthlyPayment), 
                                                                    formatter.format(interestPaid), 
                                                                    formatter.format(balanceLoan)));
            displayCount++;
        }
        return strForGui.toString();
    }
}
//use this class to display schedule on GUI
class mcFrame extends JFrame {
    //private fields
    private JFrame f;
    private JPanel inputPanel;
    private JPanel yearInputPanel, rateInputPanel, amountInputPanel,
                   calculateButtonPanel, outputPanel;
    private JLabel yearLabel, rateLabel, amountLabel;
    private JTextField year, rate, loanAmount;
    private JButton calculate;
    private JTextArea output;
    private JScrollPane scrollPane;
    //create GUI window
    public void createWindow() {
        f=new JFrame("Mortgage Calculator");
        f.setSize(400, 450);
        Container c=f.getContentPane();
        c.setLayout(new BorderLayout());
        //input panel
        inputPanel=new JPanel();
        inputPanel.setPreferredSize(new Dimension(400,80));
        inputPanel.setLayout(new FlowLayout());
            //year input panel
            yearInputPanel=new JPanel();
            yearInputPanel.setPreferredSize(new Dimension(90,50));
            yearInputPanel.setLayout(new GridLayout(2,1));
            yearLabel=new JLabel("Enter year:");
            year = new JTextField(10); //year input
            yearInputPanel.add(yearLabel);
            yearInputPanel.add(year);
            //rate input panel
            rateInputPanel=new JPanel();
            rateInputPanel.setPreferredSize(new Dimension(90,50));
            rateInputPanel.setLayout(new GridLayout(2,1));
            rateLabel=new JLabel("Enter rate:");
            rate = new JTextField(10); //interest rate input
            rateInputPanel.add(rateLabel);
            rateInputPanel.add(rate);
            //amount input panel
            amountInputPanel=new JPanel();
            amountInputPanel.setPreferredSize(new Dimension(90,50));
            amountInputPanel.setLayout(new GridLayout(2,1));
            amountLabel=new JLabel("Enter amount:");
            loanAmount = new JTextField(10); //loan amount input
            amountInputPanel.add(amountLabel);
            amountInputPanel.add(loanAmount);
            //button to start calculation
            calculateButtonPanel=new JPanel();
            calculateButtonPanel.setPreferredSize(new Dimension(90,50));
            calculateButtonPanel.setLayout(new BorderLayout());
            calculate=new JButton("Calculate"); 
            calculate.addActionListener(new ActionListener() { //handles button click event
            @Override
                public void actionPerformed(ActionEvent e) {
                    int numYear;
                    float numRate;
                    double numAmount;
                    if(year.getText().equals("") || rate.getText().equals("") || loanAmount.getText().equals(""))
                        JOptionPane.showMessageDialog(null,"Input cannot be empty!!");
                    else {                        
                        try {
                            numYear=Integer.parseInt(year.getText());
                            numRate=Float.parseFloat(rate.getText());
                            numAmount=Double.parseDouble(loanAmount.getText());
                            MortgageCalculator mortgage = new MortgageCalculator(numYear, numAmount, numRate);
                            output.setText("");
                            output.append(mortgage.displayScheduleForGui());
                        }
                        catch (NumberFormatException excp) {
                            JOptionPane.showMessageDialog(null,excp.toString());
                        }                        
                    }
                }
            });
            calculateButtonPanel.add(calculate, BorderLayout.CENTER);
        inputPanel.add(yearInputPanel);
        inputPanel.add(rateInputPanel);
        inputPanel.add(amountInputPanel);        
        inputPanel.add(calculateButtonPanel);
        c.add(inputPanel, BorderLayout.NORTH);
        
        //output panel
        outputPanel=new JPanel();
        outputPanel.setLayout(new BorderLayout());
        output = new JTextArea(); //display for output
        scrollPane = new JScrollPane(output);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        output.setEditable(false);
        outputPanel.add(scrollPane, BorderLayout.CENTER);
        c.add(outputPanel, BorderLayout.CENTER);
        
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
}