package cz.frantovo.příklady;

/**

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. If not, see <http://www.gnu.org/licenses/>.

 */

import java.awt.GridLayout;

import java.awt.HeadlessException;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JTextField;

/**

 * @author Ing. František Kučera (frantovo.cz)

 */

public class Caesar extends JFrame {

	private JTextField prostýText = new JTextField();

	private JTextField šifrovanýText = new JTextField();

	private JButton šifruj = new JButton("Šifruj");

	private JButton dešifruj = new JButton("Dešifruj");

	private static final char[] ABECEDA_ZNAKY = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();

	private static final List<Character> ABECEDA;

	private static final int SKOK = 3;

	static {

		List<Character> abeceda = new ArrayList<>();

		for (char z : ABECEDA_ZNAKY) {

			abeceda.add(z);

		}

		ABECEDA = Collections.unmodifiableList(abeceda);

	}

	public static void main(String[] args) {

		Caesar c = new Caesar();

		c.setVisible(true);

	}

	public Caesar() throws HeadlessException {

		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		setTitle("Caesarova šifra");

		setLocationRelativeTo(null);

		setLayout(new GridLayout(3, 2));

		add(new JLabel("Prostý text"));

		add(prostýText);

		add(new JLabel("Šifrovaný text"));

		add(šifrovanýText);

		add(šifruj);

		add(dešifruj);

		šifruj.addActionListener(new ActionListener() {

			@Override

			public void actionPerformed(ActionEvent e) {

				šifrovanýText.setText(posuň(prostýText.getText(), SKOK));

			}

		});

		dešifruj.addActionListener(new ActionListener() {

			@Override

			public void actionPerformed(ActionEvent e) {

				prostýText.setText(posuň(šifrovanýText.getText(), -SKOK));

			}

		});

		pack();

	}

	private static String posuň(String text, int oKolik) {

		StringBuilder posunutý = new StringBuilder(text.length());

		for (char z : text.toCharArray()) {

			posunutý.append(posuň(z, oKolik));

		}

		return posunutý.toString();

	}

	private static char posuň(char znak, int oKolik) {

		int původníPozice = ABECEDA.indexOf(znak);

		if (původníPozice < 0) {

			return znak;

		} else {

			int nováPozice = (původníPozice + oKolik) % ABECEDA_ZNAKY.length;

			nováPozice = nováPozice < 0 ? ABECEDA_ZNAKY.length + nováPozice : nováPozice;

			return ABECEDA.get(nováPozice);

		}

	}

}