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);

 		}

 	}

 }