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

/* Java class having as its purpose to test the following classes:
** Operator, ExprTree, ExprTreeAtomic, ExprTreeCompound, ExprTreeBuilder.
**
** Author: R. McCloskey
** Date: Feb. 2022
*/

public class ExprTreeTester {

   private static Scanner input; // either keyboard or file named by args[0]
   private static boolean echo;  // should input be echoed?
   private static ExprTreeBuilder exprBuilder;

   public static void main(String[] args) {
      input = establishInputSource(args.length == 0 ? null : args[0]);
      exprBuilder = new ExprTreeBuilder();

      System.out.println("Welcome to the Expression Tree Tester Program");
      boolean keepGoing = true;
      while (keepGoing) {
         try {
            keepGoing = testOneExprString();
         }
         catch (Exception e) {
            e.printStackTrace(System.out);
         }
      }
      System.out.println("\nGoodbye from the Expression Tree Tester Program");
   }

   /* Prompts the user to enter an expression-string, transforms that string
   ** into an expression-tree (i.e., an instance of ExprTree) using an
   ** instance of ExprTreeBuilder, then uses the methods of that 
   ** expression-tree to compute the value of the expression and its infix,
   ** prefix, and postfix expression-string forms.  It prints all these things.
   ** Returns true if the user entered an expression, but false if
   ** they chose the Quit option.
   */
   public static boolean testOneExprString() {
      System.out.println("\n(0) Quit");
      System.out.println("(1) Infix Expression");
      System.out.println("(2) Prefix Expression");
      System.out.println("(3) Postfix Expression");
      System.out.print("> ");

      String response = input.nextLine().trim();
      if (echo) { System.out.println(response); }
      int k = Integer.parseInt(response);
      boolean quit = false;
      if (k == 0) {
         quit = true;
      }
      else if (k < 0 || k > 3) {
         System.out.println("Invalid response!");
      }
      else {  
         ExprTree exprTree = null;
         if (k == 1) {  // infix
            System.out.print("Enter infix expression: ");
            String exprStr = input.nextLine();
            exprTree = exprBuilder.fromInfix(exprStr);
         }
         else if (k == 2) {  // prefix
            System.out.print("Enter prefix expression: ");
            String exprStr = input.nextLine();
            exprTree = exprBuilder.fromPrefix(exprStr);
         }
         else if (k == 3) {  // postfix
            System.out.print("Enter postfix expression: ");
            String exprStr = input.nextLine();
            exprTree = exprBuilder.fromPostfix(exprStr);
         }
         else {
            // impossible!!
         }

         // Having built the expression-tree, now evaluate the expression
         // it represents and display that expression in all three forms.

         System.out.println("Value is " + exprTree.valueOf());

         System.out.println("Prefix form: " +
                            exprTree.toString(ExprTree.PrefixMode));
         System.out.println("Infix form: " +
                            exprTree.toString(ExprTree.InfixMode));
         System.out.println("Postfix form: " +
                            exprTree.toString(ExprTree.PostfixMode));
      }
      return !quit;
   }


   /* If the given parameter is null, returns a Scanner attached to the
   ** keyboard; otherwise returns a Scanner attached to the file named
   ** by the parameter.
   */
   private static Scanner establishInputSource(String fileName) {
      Scanner result = null;
      if (fileName == null) {
         result = new Scanner(System.in);  // input comes from keyboard
         echo = false;
      }
      else {
         try {
            result = new Scanner(new File(fileName));
            echo = true;
         }
         catch (FileNotFoundException e) {
            System.out.println("There is no file named " + fileName);
            System.exit(1);
         }
      }
      return result;
   }


}