package comp;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Stack;

//https://github.com/blakeembrey/code-problems/blob/master/solutions/java/StackMachine.java

public class stack
{
    public int maxSize; //max size of stack
    public int top; //top of stack
    public String arr[]; //array of elements

    public stack(int n) //constructor
    {
        maxSize = n;

        arr = new String[maxSize];
        top = 0;
    }

    public boolean empty() //check for empty
    {
        if(top == 0){
            return true;
        }
        else{
            return false;
        }
    }

    public void push(String str) //push new element on to the stack
    {
        if(top < maxSize)
        {
            arr[top] = str;
            top++;
        }
        else
        {
            System.out.println("Stack OVerflow");
        }

    }
    public String pop() //pop element off of the stack and return it
    {
        if(!empty())
        {
            String temp = this.peek();
            arr[top-1] = null;
            top--;
            return temp;

        }else{
            return null;
        }
    }

    public String peek() //view top element in the stack
    {
        if(!empty())
        {
            return arr[top-1];
        }
        else
        {
            return null;
        }
    }

    public boolean isNumeric(String str)
    {
        //return str.matches("-?\\d+(\\.\\d+)?");  //match a number with optional '-' and decimal.
         try
         {
           double d = Double.parseDouble(str);
         }
         catch(NumberFormatException nfe)
         {
           return false;
         }
         return true;
    }

    public int getSize()
    {
        return top;
    }

    public String execute()
    {
        //LinkedList<String> solution = new LinkedList<String>();
        //Stack solution = new Stack();
        stack solution = new stack(5);

        int temp;
        String result = "none";

        for(int i = 0; i <= maxSize-1; i++)
        {
            String s = this.pop(); //current item being looked at

            if(empty() == true && solution.empty())//no input to computeS
            {
                System.out.println("NO STACK"); //tell user error
                return "No Stack"; //return error code
            }
            else
            {
                if(isNumeric(s)) //if numeric add to the list
                {
                    int a = Integer.parseInt(s);
                    solution.push(s);
                }
                else if(solution.getSize() >= 2) //if two there are 2 elements in the list we can perform an operation
                {
                    if(s == "+")//perform addition
                    {
                        //int x = solution.pop() + solution.pop();
                        int x = Integer.parseInt(solution.pop()) + Integer.parseInt(solution.pop());

                        String y = Integer.toString(x);
                        solution.push(y);

                    }
                    else if(s == "-")//perform subtraction
                    {
                        int x = Integer.parseInt(solution.pop()) - Integer.parseInt(solution.pop());

                        String y = Integer.toString(x);
                        solution.push(y);

                        /*int x = solution.pop() - solution.pop();
                        solution.push(x);*/
                    }
                    else if(s == "/")//perform division
                    {
                        int x = Integer.parseInt(solution.pop()) / Integer.parseInt(solution.pop());

                        String y = Integer.toString(x);
                        solution.push(y);
                    }
                    else if(s == "*")//perform multiplication
                    {
                        int x = Integer.parseInt(solution.pop()) * Integer.parseInt(solution.pop());

                        String y = Integer.toString(x);
                        solution.push(y);
                    }
                }
            }
        }
        result = solution.pop();
        return result;
    }
}