import java.util.Stack;

public class Counter {

    private Stack<Double> undoLog;
    private Stack<Double> redoLog;

    private double counter;

    public Counter() {
        counter = 0;
        undoLog = new Stack<Double>();
        redoLog = new Stack<Double>();
    }

    public double getCounter() {
        return counter;
    }

    public void count(String input) {
        if(input.equals("undo") && !undoLog.isEmpty()) {
            redoLog.push(counter);
            counter = undoLog.peek().doubleValue();
            undoLog.pop();
            System.out.println("Counter = " + counter);
            return;
        } else if(input.equals("redo") && !redoLog.isEmpty()) {
            undoLog.push(counter);
            counter = redoLog.peek().doubleValue();
            redoLog.pop();
            System.out.println("Counter = " + counter);
            return;
        } else if(input.equals("end")) {
            return;
        }
        char operation = ' ';
        double value = 0;
        try {
            value = Integer.parseInt(input.substring(1));
            operation = input.charAt(0);
        } catch (NumberFormatException e) {
            System.out.println("You must input a number as a value.");
            return;
        } catch (StringIndexOutOfBoundsException se) {
            System.out.println("You must use the correct format: operation|value. Ex. +346");
            return;
        }
        undoLog.push(counter);
        handleOperation(operation, value);
        System.out.println("Counter = " + counter);
    }

    private void handleOperation(char operation, double value) {
        redoLog.clear();
        switch(operation) {
        case '*':
        case 'x':
            counter *= value;
            break;
        case '/':
            counter /= value;
            break;
        case '+':
            counter += value;
            break;
        case '-':
            counter -= value;
            break;
        default:
            System.out.println("You must use the correct format: operation|value. Ex. +346");
            break;
        }
    }

}