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

/* BI_Calculator.java
** Author: R. McCloskey
** Date: March 2019
**
** Java application having as its purpose to test the BigInt 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, optionally preceded
** by either '+' or '-' and an <operator> is any of "+", "-", "*", "/", "%", 
** "=", "<", or ">".
** Examples: "-4509345 * 23456", "98345643345543333 < +4"
**
** 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 BigInt 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.
*/

public class BI_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 BigInt Calculator!\n");

      System.out.print("> ");
      while (scanner.hasNextLine()) {
         String expression = scanner.nextLine();
         if (echoInput) { 
            System.out.println(expression);
         }
         evaluateExpression(expression);
         System.out.print("\n> ");
      }
      System.out.println("\nGoodbye.");
   }

   /* 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();

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

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

      BigInt 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("/")) { numberResult = left.dividedBy(right); }
         else if (operator.equals("%")) { numberResult = left.mod(right); }
         else { System.out.println("Unrecognized arithmetic operator"); }
      }
      else if (relationalOperators.contains(operator)) {
         if (operator.equals("=")) { boolResult = left.equals(right); }
         else if (operator.equals("<")) { boolResult = left.isLessThan(right); }
         else if (operator.equals(">")) { boolResult = left.isGreaterThan(right); }
         else { System.out.println("Unrecognized relational operator"); }
      }
      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."); }
   }
   
}