/*
 * Copyright (c) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017 David Berkman
 * 
 * This file is part of the SmallMind Code Project.
 * 
 * The SmallMind Code Project is free software, you can redistribute
 * it and/or modify it under either, at your discretion...
 * 
 * 1) The terms of GNU Affero General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at
 * your option) any later version.
 * 
 * ...or...
 * 
 * 2) The terms of the Apache License, Version 2.0.
 * 
 * The SmallMind Code Project 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 or Apache License for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License
 * and the Apache License along with the SmallMind Code Project. If not, see
 * <http://www.gnu.org/licenses/> or <http://www.apache.org/licenses/LICENSE-2.0>.
 * 
 * Additional permission under the GNU Affero GPL version 3 section 7
 * ------------------------------------------------------------------
 * If you modify this Program, or any covered work, by linking or
 * combining it with other code, such other code is not for that reason
 * alone subject to any of the requirements of the GNU Affero GPL
 * version 3.
 */
package org.smallmind.nutsnbolts.io;

import java.io.File;
import java.io.FileFilter;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;

public class FileIterable implements Iterable<File> {

  private final File directory;
  private final FileFilter fileFilter;

  public FileIterable (File directory) {

    this(directory, null);
  }

  public FileIterable (File directory, FileFilter fileFilter) {

    this.directory = directory;
    this.fileFilter = fileFilter;
  }

  public Iterator<File> iterator () {

    return new FileIterator();
  }

  private class FileIterator implements Iterator<File> {

    private LinkedList<File> directoryStack;
    private File currentFile;

    public FileIterator () {

      if (!directory.exists()) {
        throw new IllegalArgumentException("Specified directory(" + directory.getAbsolutePath() + ") doesn't exist");
      } else if (!directory.isDirectory()) {
        throw new IllegalArgumentException("Specified file(" + directory.getAbsolutePath() + ") isn't a directory");
      }

      directoryStack = new LinkedList<>();
      directoryStack.add(directory);

      currentFile = getNextFile();
    }

    private File getNextFile () {

      File file;

      while (!directoryStack.isEmpty()) {
        file = directoryStack.removeFirst();
        if (file.isDirectory()) {

          LinkedList<File> appendedList = new LinkedList<>();

          for (File child : file.listFiles(fileFilter)) {
            if (child.isFile()) {
              appendedList.addFirst(child);
            } else {
              appendedList.addLast(child);
            }
          }

          if (!appendedList.isEmpty()) {
            directoryStack.addAll(0, appendedList);
          }
        } else {
          return file;
        }
      }

      return null;
    }

    public boolean hasNext () {

      return currentFile != null;
    }

    public File next () {

      File nextFile;

      if (currentFile == null) {
        throw new NoSuchElementException();
      }

      nextFile = currentFile;
      currentFile = getNextFile();

      return nextFile;
    }

    public void remove () {

      throw new UnsupportedOperationException();
    }
  }
}