import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

/* UNatCalculator.java
** Author: R. McCloskey
** Date: February 2019  (updated Feb. 2026)
**
** Java application having as its purpose to test the UnboundedNatural
** class.  It serves as, in effect, a calculator that interprets each
** line of input as an expression to be evaluated, where the expression
** is expected to have the form
**
**                <int_numeral> <operator> <int_numeral>
**
** An <int_numeral> is a sequence of (decimal) digits and an <operator>
** is any of "=", "+", "-", or "*".
** Examples: "4509345 - 23456", "98345643345543333 * 4678023"
**
** In response to each expression provided as input, the program displays 
** the result of applying the given operator to the given numbers, making
** use of the methods of the UnboundedNatural class.
**
** If a command line argument is provided, it is taken to be the name of
** the file containing input data.  Otherwise, input is read from standard
** input.  A blank line entered as input is taken to mean that the program
** is to terminate.
*/

public class Calculator {

   public static void main(String[] args) throws FileNotFoundException {
      Scanner scanner;
      boolean echoInput;
      if (args.length != 0) {
         scanner = new Scanner(new File(args[0])); 
         echoInput = true;
      }
      else {
         scanner = new Scanner(System.in);
         echoInput = false;
      }

      System.out.println("Welcome to the UnboundedNatural Calculator!\n");

      boolean keepGoing = true;
      System.out.print("> ");
      while (keepGoing) {
         String expression = scanner.nextLine().trim();
         
         if (expression.length() == 0) {
            keepGoing = false;
         }
         else {
            if (echoInput) { System.out.println(expression); }
            try {
               evaluateExpression(expression);
            }
            catch (Exception e) {
               e.printStackTrace(System.out);
            }
            System.out.print("\n> ");
         }
      }
      System.out.println("Goodbye.");
   }

   /* Evaluates the given expression and displays the result.
   */
   public static void evaluateExpression(String expression) {

      Scanner exprScanner = new Scanner(expression);
      String numeral1 = exprScanner.next();
      String operator = exprScanner.next();
      String numeral2 = exprScanner.next();

      UnboundedNatural left = new UnboundedNatural(numeral1);
      UnboundedNatural right = new UnboundedNatural(numeral2);

      System.out.printf("Computing %s %s %s\n", left, operator, right);  

      UnboundedNatural numberResult = null;
      Boolean boolResult = null;

      String arithOperators = "+-*/%";
      String relationalOperators = "=<>";

      if (arithOperators.contains(operator)) {
         if (operator.equals("+"))      { numberResult = left.plus(right); }
         else if (operator.equals("-")) { numberResult = left.minus(right); }
         else if (operator.equals("*")) { numberResult = left.times(right); }
         else if (operator.equals("/")) { 
            System.out.println("The division operator is not supported.");
            //numberResult = left.dividedBy(right);
         }
         else if (operator.equals("%")) { 
            System.out.println("The remainder operator is not supported.");
            //numberResult = left.mod(right);
         }
      }
      else if (relationalOperators.contains(operator)) {
         if (operator.equals("=")) { boolResult = left.equals(right); }
         else if (operator.equals("<")) { 
            System.out.println("The less-than operator is not supported.");
            // boolResult = left.isLessThan(right);
         }
         else if (operator.equals(">")) { 
            System.out.println("The greater-than operator is not supported.");
            // boolResult = left.isGreaterThan(right); 
         }
      }
      else { 
         System.out.println("Unrecognized operator");
      }

      if (numberResult != null) { System.out.println(numberResult); }
      else if (boolResult != null) { System.out.println(boolResult); }
      else { System.out.println("No result was computed."); }
   }
   
}