Added methods to delete songs and song groups.

- OsuGroupList.get().deleteSongGroup() will delete a song group from the list.
- OsuGroupList.get().deleteSong() will delete an individual song from the list (must be expanded), and will delete the song group if there are no remaining songs in the group.
- If possible, deleted beatmap files are moved to system trash (using JNA); otherwise, they are deleted immediately.  This is done through Utils.deleteToTrash().

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/Utils.java

@@ -25,6 +25,7 @@ import itdelatrisu.opsu.downloads.DownloadNode;
 import java.awt.Font;
 import java.awt.image.BufferedImage;
 import java.io.File;
+import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.IntBuffer;
 import java.text.SimpleDateFormat;
@@ -55,6 +56,8 @@ import org.newdawn.slick.state.StateBasedGame;
 import org.newdawn.slick.util.Log;
 import org.newdawn.slick.util.ResourceLoader;
 
+import com.sun.jna.platform.FileUtils;
+
 /**
  * Contains miscellaneous utilities.
  */
@@ -738,4 +741,60 @@ public class Utils {
 	    }
 	    return cleanName.toString();
 	}
+
+	/**
+	 * Deletes a file or directory.  If a system trash directory is available,
+	 * the file or directory will be moved there instead.
+	 * @param file the file or directory to delete
+	 * @return true if moved to trash, and false if deleted
+	 * @throws IOException if given file does not exist
+	 */
+	public static boolean deleteToTrash(File file) throws IOException {
+		if (file == null)
+			throw new IOException("File cannot be null.");
+		if (!file.exists())
+			throw new IOException(String.format("File '%s' does not exist.", file.getAbsolutePath()));
+
+		// move to system trash, if possible
+		FileUtils fileUtils = FileUtils.getInstance();
+		if (fileUtils.hasTrash()) {
+			try {
+				fileUtils.moveToTrash(new File[] { file });
+				return true;
+			} catch (IOException e) {
+				Log.warn(String.format("Failed to move file '%s' to trash.", file.getAbsolutePath()), e);
+			}
+		}
+
+		// delete otherwise
+		if (file.isDirectory())
+			deleteDirectory(file);
+		else
+			file.delete();
+		return false;
+	}
+
+	/**
+	 * Recursively deletes all files and folders in a directory, then
+	 * deletes the directory itself.
+	 * @param dir the directory to delete
+	 */
+	private static void deleteDirectory(File dir) {
+		if (dir == null || !dir.isDirectory())
+			return;
+
+		// recursively delete contents of directory
+		File[] files = dir.listFiles();
+		if (files != null && files.length > 0) {
+			for (File file : files) {
+				if (file.isDirectory())
+					deleteDirectory(file);
+				else
+					file.delete();
+			}
+		}
+
+		// delete the directory
+		dir.delete();
+	}
 }