// Name : Matthew Reeves 
// This is a program to read and process postfix expressions

import java.util.Scanner;
import ListPkg.Stack;
import ListPkg.LinkedList;
import ExceptionPkg.EmptyListException;
import java.util.InputMismatchException;

public class Postfix
{
	//main method accepts user input to process a postfix expression	

	public static void main( String args[] )
	{
		Scanner input=new Scanner(System.in);

		Stack stacker=new Stack("testStack");

		System.out.println("\nThank you for using the Postfix calculator program!\n");

		//creates all necessary instance variables

		char keepcalc='y';
		char oper='q';
		double value;
		Double wrappedValue;
		Double x;
		Double y;
	
		//this loop continues to run as long as user wants to enter in new postfix expressions		

		do
		{
			System.out.print("Please enter an expression in postfix notation to evaluate. \nSeparate all operators/operands with spaces, and end expression with '=':\n\n\t");

			//this loops continues to run as long user keeps entering operators/operands for an expression			

			do
			{
				try
				{
					value=input.nextDouble();
					wrappedValue=value;
					stacker.push(wrappedValue);
					
				}
	
				catch (InputMismatchException inputMismatchException) 
				{
					oper=input.next().charAt(0);					
	
					switch(oper)
					{
						case '+': 
	
							if (stacker.isEmpty())
							{
								continue;
							}
	
							y=(Double)stacker.pop();
					
							if (stacker.isEmpty())
							{
								continue;
							}

							x=(Double)stacker.pop();

							stacker.push(x+y);
							continue;

						case '-':
	
							if (stacker.isEmpty())
							{
								continue;
							}

							y=(Double)stacker.pop();
					
							if (stacker.isEmpty())
							{
								continue;
							}

							x=(Double)stacker.pop();
							stacker.push(x-y);
							continue;
						
						case '*':

							if (stacker.isEmpty())
							{
								continue;
							}

							y=(Double)stacker.pop();
					
							if (stacker.isEmpty())
							{
								continue;
							}

							x=(Double)stacker.pop();
							stacker.push(x*y);
							continue;
	
						case '/':

							if (stacker.isEmpty())
							{
								continue;
							}

							y=(Double)stacker.pop();
					
							if (stacker.isEmpty())
							{
								continue;
							}

							x=(Double)stacker.pop();
							stacker.push(x/y);
							continue;

						case '^':

							if (stacker.isEmpty())
							{
								continue;
							}

							y=(Double)stacker.pop();
					
							if (stacker.isEmpty())
							{
								continue;
							}
	
							x=(Double)stacker.pop();
							stacker.push(Math.pow(x,y));
							continue;

						case '=':
	
							if (stacker.isEmpty())
							{
								System.out.println("\nInvalid expression entered, cannot evaluate");
								continue;
							}

							wrappedValue=(Double)stacker.pop();

							if (stacker.isEmpty())
							{	
								System.out.printf("\n==============================\n\n\tResult = %f\n\n==============================\n\n",wrappedValue);	
								continue;
							}
							else
							{
								System.out.println("\nInvalid expression entered, cannot evaluate");
								continue;
							}
					}
				}

			}while(oper!='=');			

			input.nextLine();

			System.out.print("\n--------------------------------------------------\nWould you like to enter a new expression? (Y/N) ");
			keepcalc=input.next().charAt(0);					
			System.out.print("--------------------------------------------------\n\n");
			stacker.Clear();

			oper='q';			
	
		}while(keepcalc=='y' || keepcalc=='Y');
	}
}