/* Car Loan Estimator
**
** Java application that prints a table showing the monthly payments for 
** car loan with annual interest rates ranging from 1% to 10% and terms
** ranging from 12 months to 72 months.
**
** CMPS 134  Fall 2025  Prog. Assg. #2
** Authors: P.M.J. and R.W.M. 
*/

public class CarLoanEstimator {

   // CONSTANTS
   static final int TERM_START = 12;                      //Shortest term in months
   static final int TERM_LIMIT = 72;                      //Longest term in months
   static final double ANNUAL_INTEREST_RATE_START = 1.0;  //Lowest Annual Interest Rate
   static final double ANNUAL_INTEREST_RATE_LIMIT = 10.0; //Hightest Annual Interest Rate
 
   // GLOBAL VARIABLES
   static double principal = 25000.00;    //Principal to be borrowed
   static double annualInterestRate;      //Annual Interest Rate 
   static int term;                       //term (in months)
   
   static double payment;                 //Calculated monthly payment

   public static void main( String [] args ) {
      System.out.printf("Monthly payments for a $%8.2f loan%n", principal); 
      printHeading();
      printTable();
      System.out.println("Done!!");
   }
   
   public static void printHeading() {
      String underline = "---||";
      System.out.print("   ||  ");
      for (annualInterestRate = ANNUAL_INTEREST_RATE_START; 
           annualInterestRate <= ANNUAL_INTEREST_RATE_LIMIT; 
           annualInterestRate = annualInterestRate + 1.0)
      {
         System.out.printf("%6.2f %% |  ", annualInterestRate);
         underline = underline + "-----------|";
      }
      System.out.println();
      System.out.println(underline);      
   }
   
   public static void printTable() {
      for(term = TERM_START; term <= TERM_LIMIT; term = term + 12) {
         printRow();
      }
   }
   
   public static void printRow() {
      System.out.printf("%2d ||  ",term);
      for(annualInterestRate = ANNUAL_INTEREST_RATE_START; 
             annualInterestRate <= ANNUAL_INTEREST_RATE_LIMIT; 
             annualInterestRate = annualInterestRate + 1.0)
      {
         calculatePayment();
         System.out.printf("%8.2f |  ", payment);
      }
      System.out.println();
   }
   
   /* Uses the global variables 'principal', 'annualInterestRate', and 'term'
   ** to determine a value for payment.  An explanation of the formula used
   ** may be viewed at: https://www.youtube.com/watch?v=p8f8XP2tmvE
   */
   public static void calculatePayment() {
      double monthlyInterestRate = (annualInterestRate / 100) / 12;

      double numerator = principal * monthlyInterestRate;
      double denominator = 1 - Math.pow((1 + monthlyInterestRate),(0.0-term));
      payment = numerator / denominator;
   }

}