02. Song Encryption

package ExamPrep;

import java.util.Scanner;
import java.util.regex.Pattern;

public class SongEncryption {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        String line = scanner.nextLine();
        while (!"end".equals(line)) {
            String[] token = line.split(":");
            String artist = token[0];
            String song = token[1];
            if (isValidArtist(artist) && isValidSong(song)) {
                int key = artist.length() % ('z' - 'a' + 1);
                String enArtist = encrypt(artist, key);
                String enSong = encrypt(song, key);
                System.out.printf("Successful encryption: %s@%s%n", enArtist, enSong);
            } else {
                System.out.println("Invalid input!");
            }
            line = scanner.nextLine();
        }

    }

    private static String encrypt(String artist, int key) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < artist.length(); i++) {
            char ch = artist.charAt(i);
            char encryptCh;
            if (ch == ' ' || ch == '\'') {
                encryptCh = ch;
            } else {
                encryptCh = (char) (ch + key);
                if (Character.isUpperCase(ch) && encryptCh > 'Z') {
                    encryptCh = (char) ('A' + (encryptCh - 'Z' - 1));
                }
                if (Character.isLowerCase(ch) && encryptCh > 'z') {
                    encryptCh = (char) ('a' + (encryptCh - 'z' - 1));
                }
            }
            sb.append(encryptCh);
        }
        return sb.toString();
    }


    private static boolean isValidSong(String song) {
        return Pattern.compile("([A-Z ]+)").matcher(song).matches();
    }

    private static boolean isValidArtist(String artist) {
        return Pattern.compile("([A-Z][a-z ']+)").matcher(artist).matches();
    }
}