package Project.Arithmetic;

import java.util.*;

public class InfixToSuffix
{
    private Stack<String> stack;
    private List<String> list;

    private String message, Message = "";


    public InfixToSuffix() {
        stack = new Stack<String>();   //  Store operator
        list = new ArrayList<String>();   //  Store operation number and operator
    }

    public void conversion(String expr) {
        String token;
        StringTokenizer tokenizer = new StringTokenizer(expr);

        while (tokenizer.hasMoreTokens()) {
            //  If tokenizer has the next value, loop and assign value.
            token = tokenizer.nextToken();

            if (token.equals("(")) {
                //  If the value of the token is the left parenthesis, then the stack
                stack.push(token);
            }else if (token.equals("+") || token.equals("-")) {
                //  If the value of token is "+" or "-", once again determine whether the stack is empty.
                if (!stack.empty()){
                    //  If the stack is not empty, judge what is the top element of the stack
                    if (stack.peek().equals("(")) {
                        //  If the top of the stack is "(", the operator enters the stack
                        stack.push(token);
                    }else{
                        //  Otherwise, remove the stack top elements first, add them to the list,
                        //  and then stack the operators into the stack.
                        list.add(stack.pop());
                        stack.push(token);
                    }
                }else {
                    //  Otherwise the operator enters the stack
                    stack.push(token);
                }
            }else if (token.equals("*") || token.equals("÷")){
                //  If the value of token is "*" or "÷", it again determines whether the stack is empty.
                if (!stack.empty()) {
                    //  If the stack is not empty, judge what is the top element of the stack
                    if (stack.peek().equals("*") || stack.peek().equals("÷")) {
                        //  If the top of the stack is "*" or "÷", remove the stack top elements first,
                        //  add them to the list, and then stack the operators into the stack.
                        list.add(stack.pop());
                        stack.push(token);
                    }else {
                        //  In addition, the operator directly enters the stack.
                        stack.push(token);
                    }
                }else {
                    //  If the stack is empty, the operator goes directly to the stack
                    stack.push(token);
                }
            } else if (token.equals(")")) {
                //  If encounter "), starts to circulate
                while (true) {
                    //  Remove the top element of the stack and assign it to A
                    String A = stack.pop();
                    if (!A.equals("(")) {
                        //  If A is not "(", it is added to the list
                        list.add(A);
                    } else {
                        //  If A is "(", exit the loop
                        break;
                    }
                }
            }else {
                //  If it is an arithmetic number, enter the list
                list.add(token);
            }
        }
        while (!stack.empty()) {
            //  Remove elements from the stack and add them to the list until the stack is empty.
            list.add(stack.pop());
        }
        ListIterator<String> li = list.listIterator();
        while (li.hasNext()) {
            Message += li.next() + " ";
            //  The elements in iterator are taken out in turn, and spaces are used as separators.
            li.remove();
        }
        message = Message;
    }

    public String getMessage() {
        return message;
    }
}