import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

// the calculator takes care of the actual calcualtions, and stores the
// current number this class extends the JLabel so it can also serve as
// a display of the current number
public class Calculator extends JLabel {
    // the state which we are in
    private CalculatorState state;

    // the current value we are using
    private double value;

    // the saved value if we are doing an operator
    private double saved;

    // whether or not new digits are being added after the dot
    private boolean dot;

    // the amount of places after the dot to add
    private int place;

    public Calculator() {
        // clear should initialize us to 0, so just call that
        clear();
    }

    // called to clear out the calculator
    public void clear() {
        // set all the default values
        value = 0.0;
        saved = 0.0;
        dot = false;
        place = 0;
        state = CalculatorState.DEFAULT;

        // update the display
        update();
    }

    // update the display with the current value
    public void update() {
        // convert the value to a string
        String stringValue = Double.toString(value);

        // since we are a JLabel, we have a setText function, just call it
        setText(stringValue);
    }

    // called when the user pushes one of the digit buttons
    public void addDigit(int digit) {
        // if the state is done, reset things first
        if (state == CalculatorState.DONE) {
            clear();
        }

        // if there has not been a dot yet
        if (!dot) {
            // add this digit to the end, but multiplying the current value
            // by ten and then adding it in
            value = value * 10 + digit;
        } else {
            // add this digit in the next decimal place available
            value = value + digit / (Math.pow(10.0, place));
            place++;
        }

        // update the display
        update();
    }

    // called when equals gets pushed
    public void equals() {
        // apply the operator depending on our state
        switch (state) {
            case DEFAULT:
                // do nothing!
                break;
            case ADDING:
                value = saved + value;
                break;
            case SUBTRACTING:
                value = saved - value;
                break;
            case MULTIPLYING:
                value = saved * value;
                break;
            case DIVIDING:
                value = saved / value;
                break;
        }
        // update to the new value
        update();

        // go to the DONE state
        state = CalculatorState.DONE;
    }

    // called when the dot button is pushed
    public void setDot() {
        // if we already hada a dot, this is an error!
        if (dot) {
            throw new IllegalStateException("Can't have two decimal points");
        }

        // set the dot
        dot = true;
        place = 1;
    }

    // called when an operator button is pushed
    public void setOperator(char operator) {
        // save the current value;
        saved = value;

        // reset value to read
        value = 0.0;
        dot = false;
        place = 0;

        // remember the operator so we can apply it later
        switch (operator) {
            case '+':
                state = CalculatorState.ADDING;
                break;
            case '-':
                state = CalculatorState.SUBTRACTING;
                break;
            case '*':
                state = CalculatorState.MULTIPLYING;
                break;
            case '/':
                state = CalculatorState.DIVIDING;
                break;
            default:
                throw new IllegalArgumentException("Invalid Operator");
        }
    }

    // called for the square root operation
    public void sqrt() {
        value = Math.sqrt(value);
        update();
    }
}