package Project.Arithmetic;

import java.util.StringTokenizer;
import java.util.Stack;

public class Calculator
{
    private final char ADD = '+';
    private final char SUBTRACT = '-';
    private final char MULTIPLY = '*';
    private final char DIVIDE = '÷';

    private Stack<String> stack;
    private RationalNumber r, r1, r2;

    public  boolean isOperator (String token)
    {
        return ( token.equals("+") || token.equals("-") ||
                token.equals("*") || token.equals("÷") );
    }

    public String evalSingleOp (char operation, RationalNumber op1, RationalNumber op2)
    {
        RationalNumber result = new RationalNumber(0,1);

        switch (operation)
        {
            case ADD:
                result = r1.add(r2);
                break;
            case SUBTRACT:
                result = r1.subtract(r2);
                break;
            case MULTIPLY:
                result = r1.multiply(r2);
                break;
            case DIVIDE:
                result = r1.divide(r2);
        }

        return result.toString();
    }

    public RationalNumber tranIntoRationalNum (String s){
        String token1, token2;

        StringTokenizer tokenizer1 = new StringTokenizer(s, "/");//   Divide the operation number to "/" as a mark
        token1 = tokenizer1.nextToken();
        if (tokenizer1.hasMoreTokens()) {//  If there are second elements, token1 is placed in the position of the molecule,
                                         //  and token2 is placed in the denominator.
            token2 = tokenizer1.nextToken();
            r = new RationalNumber(Integer.parseInt(token1), Integer.parseInt(token2));
        }
        else {//  If there are no second elements, the token1 will be placed in the molecular position and the denominator will be fixed to 1.
            r = new RationalNumber(Integer.parseInt(token1),1);
        }
        return r;
    }

    public Calculator() {
        stack = new Stack<String>();
    }

    public String evaluate (String expr)
    {
        String op1, op2, result = null;
        String token;
        StringTokenizer tokenizer = new StringTokenizer (expr);
        while (tokenizer.hasMoreTokens())
        {
            token = tokenizer.nextToken();

            //   If it is the operator, call isOperator
            if (isOperator(token))
            {
                //  From the stack, the number of operands is popped up to 2 and converted to RationalNumber type.
                op2 = stack.pop();
                r2 = tranIntoRationalNum(op2);
                //  From the stack, the number of operands is popped up to 1 and converted to RationalNumber type.
                op1 = stack.pop();
                r1 = tranIntoRationalNum(op1);
                //  EvalSingleOp is calculated by calling the result according to the operator and two operands.
                result = evalSingleOp(token.toCharArray()[0], r1, r2);
                //  Compute the result and enter the stack
                result = stack.push(result);
            }
            else //  If it is an operand enter the stack
                stack.push(token);
        }
        return result;
    }
}