Documented helper classes in util package

Also did minor code cleanup

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/CryptoHelper.java

@@ -15,18 +15,28 @@ import java.security.spec.KeySpec;
 
 public class CryptoHelper {
 
+    /**
+     * Creates a <code>javax.crypto.SecretKey</code> from a provided password
+     * @param pass The password
+     * @return the generated secret key
+     */
     public static SecretKey createKeyFromPassword(String pass){
         try {
             KeySpec spec = new PBEKeySpec(pass.toCharArray(), "abcdefghijklmnop".getBytes(), 65536, 256); // AES-256
             SecretKeyFactory f = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
-            byte[] key = new byte[0];
+            byte[] key = f.generateSecret(spec).getEncoded();
-            key = f.generateSecret(spec).getEncoded();
             return new SecretKeySpec(key, "AES");
         } catch (InvalidKeySpecException | NoSuchAlgorithmException e) {
             throw new RuntimeException(e);
         }
     }
 
+    /**
+     * Saves a <code>java.io.Serializable</code> Object into an encrypted file
+     * @param obj The object to save
+     * @param file The Path where to save the file
+     * @param key The SecretKey (AES) to encrypt the file with
+     */
     public static void serializeEncrypted(Serializable obj, Path file, SecretKey key){
         try {
             if(file.toFile().exists()) file.toFile().delete();
@@ -45,8 +55,14 @@ public class CryptoHelper {
         }
     }
 
+    /**
+     * Reads an encrypted file into a <code>java.io.Serializable</code> object.
+     * @param file The <code>java.nio.Path</code> where the encrypted file is stored.
+     * @param key The SecretKey (AES) to decrypt the file with
+     * @return The <code>java.io.Serializable</code> object read from the file.
+     */
     public static Serializable deserializeEncrypted(Path file, SecretKey key) {
-        Serializable ret = null;
+        Serializable ret;
         try {
             Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
             IvParameterSpec iv = new IvParameterSpec("abcdefghijklmnop".getBytes());

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/FileHelper.java

@@ -7,6 +7,11 @@ import java.util.Base64;
 
 public class FileHelper {
 
+    /**
+     * Reads a file and encodes it into Base64
+     * @param file The file to read
+     * @return A Base64 encoded String containing the data of the file
+     */
     public static String encodeFileToBase64(File file){
         String encodedfile = null;
         try (FileInputStream fileInputStreamReader = new FileInputStream(file)){

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/Logger.java

@@ -4,6 +4,11 @@ import static de.b00tload.tools.lastfmtospotifyplaylist.LastFMToSpotify.configur
 
 public class Logger {
 
+    /**
+     * Logs the provided String to console if the option <code>logging.level</code> in the configuration is higher or equal to the provided priority
+     * @param string The String to log
+     * @param priority The minimum logging level with which the provided string should be logged
+     */
     public static void logLn(String string, int priority){
         if(Integer.parseInt(configuration.get("logging.level"))>=priority){
             System.out.println(string);

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/PeriodHelper.java

@@ -4,6 +4,11 @@ import de.umass.lastfm.Period;
 
 public class PeriodHelper {
 
+    /**
+     * Converts a provided String (<code>de.umass.lastfm.Period.getString()</code>) into the corresponding <code>de.umass.lastfm.Period</code>
+     * @param string The value to be converted into a <code>de.umass.lastfm.Period</code>
+     * @return The converted <code>de.umass.lastfm.Period</code>, defaults to <code>de.umass.lastfm.Period.ONE_MONTH</code>
+     */
     public static Period getPeriodByString(String string){
         for(Period p : Period.values()){
             if(p.getString().equalsIgnoreCase(string)) return p;

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/TimeHelper.java

@@ -5,19 +5,33 @@ import java.time.ZoneId;
 
 public class TimeHelper {
 
+    /**
+     * Gets the hours of the UTC offset from a LocalDateTime, which is asserted to be at the system default Timezone (<code>ZoneId.systemDefault()</code>)
+     * @param now The <code>java.time.LocalDateTime</code> for which the offset should be calculated
+     * @return The hours of offset from UTC
+     */
     public static int getUTCOffsetHours(LocalDateTime now){
-
         return (int) Math.floor((double) now.atZone(ZoneId.systemDefault()).getOffset().getTotalSeconds()/3600);
     }
 
+    /**
+     * Gets the minutes of the UTC offset from a LocalDateTime, which is asserted to be at the system default Timezone (<code>ZoneId.systemDefault()</code>)
+     * @param now The <code>java.time.LocalDateTime</code> for which the offset should be calculated
+     * @return The minutes of offset from UTC
+     */
     public static int getUTCOffsetMinutes(LocalDateTime now){
         return (now.atZone(ZoneId.systemDefault()).getOffset().getTotalSeconds()/60);
     }
 
+    /**
+     * Generates an ISO 8601 complying String containing the UTC offset from a LocalDateTime, which is asserted to be at the system default Timezone (<code>ZoneId.systemDefault()</code>)
+     * @param now The <code>java.time.LocalDateTime</code> for which the offset should be calculated
+     * @return an ISO 8601 complying String containing the UTC offset (e.g. "+01:00")
+     */
     public static String getUTCOffset(LocalDateTime now){
         int hour = getUTCOffsetHours(now);
         String h = (hour == Math.abs(hour) ? "+" : "-") + (String.valueOf(Math.abs(hour)).length() == 1 ? "0" + Math.abs(hour) : String.valueOf(Math.abs(hour)));
-        int min = Math.abs(getUTCOffsetMinutes(now))-(Math.abs(hour)*60);
+        int min = Math.abs(getUTCOffsetMinutes(now))%(Math.abs(hour));
         String m = (String.valueOf(Math.abs(min)).length() == 1 ? "0" + Math.abs(min) : String.valueOf(Math.abs(min)));
         return h + ":" + m;
     }

src/main/java/de/b00tload/tools/lastfmtospotifyplaylist/util/TokenHelper.java

@@ -8,14 +8,27 @@ import static de.b00tload.tools.lastfmtospotifyplaylist.LastFMToSpotify.USER_HOM
 import static de.b00tload.tools.lastfmtospotifyplaylist.LastFMToSpotify.configuration;
 
 public class TokenHelper {
+
+    /**
+     * Manages saving a <code>se.michaelthelin.spotify.model_objects.credentials.AuthorizationCodeCredentials</code> into "~/.lfm2s/spotify.lfm2scred" using <code>de.b00tload.tools.lastfmtospotifyplaylist.util.CryptoHelper.serializeEncrypted(...)</code>
+     * @param cred The <code>se.michaelthelin.spotify.model_objects.credentials.AuthorizationCodeCredentials</code> to be saved
+     */
     public static void saveTokens(AuthorizationCodeCredentials cred) {
         CryptoHelper.serializeEncrypted(cred, Path.of(USER_HOME, "/.lfm2s/spotify.lfm2scred"), CryptoHelper.createKeyFromPassword(configuration.get("cache.crypto")));
     }
 
+    /**
+     * Manages retrieving a <code>se.michaelthelin.spotify.model_objects.credentials.AuthorizationCodeCredentials</code> from "~/.lfm2s/spotify.lfm2scred" using <code>de.b00tload.tools.lastfmtospotifyplaylist.util.CryptoHelper.deserializeEncrypted(...)</code>
+     * @return The retrieved <code>se.michaelthelin.spotify.model_objects.credentials.AuthorizationCodeCredentials</code>
+     */
     public static AuthorizationCodeCredentials fetchTokens() {
         return (AuthorizationCodeCredentials) CryptoHelper.deserializeEncrypted(Path.of(USER_HOME, "/.lfm2s/spotify.lfm2scred"), CryptoHelper.createKeyFromPassword(configuration.get("cache.crypto")));
     }
 
+    /**
+     * Checks whether the saved spotify AuthorizationCodeCredentials at "~/.lfm2s/spotify.lfm2scred" exist
+     * @return true if file exists, false if not
+     */
     public static boolean existsTokens(){
         return Path.of(USER_HOME, "/.lfm2s/spotify.lfm2scred").toFile().exists();
     }