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/*
 * Copyright (c) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016 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
 *  or .
 * 
 * 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.HashSet;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class FileProcessorQueue {

  private static enum State {

    STARTED, STOPPED
  }

  private ReentrantLock exclusiveLock;
  private Condition emptyCondition;
  private FileProcessorGopher fileProcessorGopher;
  private LinkedList waitingQueue;
  private HashSet waitingSet;
  private HashSet processingSet;
  private File directory;
  private FileFilter fileFilter;
  private TimeUnit timeUnit;
  private AtomicReference atomicState = new AtomicReference(State.STOPPED);
  private boolean removeEmptyDirectories = false;
  private long pulse;

  public FileProcessorQueue () {

    waitingQueue = new LinkedList();
    waitingSet = new HashSet();
    processingSet = new LinkedHashSet();

    exclusiveLock = new ReentrantLock();
    emptyCondition = exclusiveLock.newCondition();
  }

  public FileProcessorQueue (File directory, long pulse, TimeUnit timeUnit) {

    this(directory, null, false, pulse, timeUnit);
  }

  public FileProcessorQueue (File directory, boolean removeEmptyDirectories, long pulse, TimeUnit timeUnit) {

    this(directory, null, removeEmptyDirectories, pulse, timeUnit);
  }

  public FileProcessorQueue (File directory, FileFilter fileFilter, long pulse, TimeUnit timeUnit) {

    this(directory, fileFilter, false, pulse, timeUnit);
  }

  public FileProcessorQueue (File directory, FileFilter fileFilter, boolean removeEmptyDirectories, long pulse, TimeUnit timeUnit) {

    this();

    this.directory = directory;
    this.fileFilter = fileFilter;
    this.removeEmptyDirectories = removeEmptyDirectories;
    this.pulse = pulse;
    this.timeUnit = timeUnit;
  }

  public void setDirectory (File directory) {

    this.directory = directory;
  }

  public File getDirectory () {

    return directory;
  }

  public void setFileFilter (FileFilter fileFilter) {

    this.fileFilter = fileFilter;
  }

  public void setRemoveEmptyDirectories (boolean removeEmptyDirectories) {

    this.removeEmptyDirectories = removeEmptyDirectories;
  }

  public void setPulse (long pulse) {

    this.pulse = pulse;
  }

  public void setTimeUnit (TimeUnit timeUnit) {

    this.timeUnit = timeUnit;
  }

  public void push (File file) {

    push(file, false);
  }

  public void push (File file, boolean forced) {

    exclusiveLock.lock();
    try {
      if ((forced || atomicState.get().equals(State.STARTED)) && file.exists()) {
        if (!(waitingSet.contains(file) || processingSet.contains(file))) {
          waitingQueue.addLast(file);
          waitingSet.add(file);

          emptyCondition.signal();
        }
      }
    }
    finally {
      exclusiveLock.unlock();
    }
  }

  public File poll ()
    throws InterruptedException {

    return poll(0, TimeUnit.MILLISECONDS);
  }

  public File poll (long timeout, TimeUnit timeUnit)
    throws InterruptedException {

    File file;
    boolean unexpired = true;

    exclusiveLock.lock();
    try {
      while (unexpired && atomicState.get().equals(State.STARTED) && waitingQueue.isEmpty()) {
        unexpired = emptyCondition.await(timeout, timeUnit);
      }

      if (unexpired && atomicState.get().equals(State.STARTED)) {
        waitingSet.remove(file = waitingQueue.removeFirst());
        processingSet.add(file);

        return file;
      }

      return null;
    }
    finally {
      exclusiveLock.unlock();
    }
  }

  public void delete (File file)
    throws FileProcessingException {

    exclusiveLock.lock();
    try {
      if (!processingSet.contains(file)) {
        throw new FileProcessingException("File(%s) is not currently marked for processing", file.getAbsolutePath());
      }

      processingSet.remove(file);
      if (!file.delete()) {
        throw new FileProcessingException("Unable to delete the file(%s)", file.getAbsolutePath());
      }

      if (removeEmptyDirectories && (file.getParentFile().list().length == 0)) {
        if (!file.getParentFile().delete()) {
          throw new FileProcessingException("Unable to delete the empty directory(%s)", file.getParentFile().getAbsolutePath());
        }
      }
    }
    finally {
      exclusiveLock.unlock();
    }
  }

  public void start () {

    if (atomicState.compareAndSet(State.STOPPED, State.STARTED)) {
      new Thread(fileProcessorGopher = new FileProcessorGopher(this, directory, fileFilter, pulse, timeUnit)).start();
    }
  }

  public void stop ()
    throws InterruptedException {

    if (atomicState.compareAndSet(State.STARTED, State.STOPPED)) {
      fileProcessorGopher.finish();
    }
  }
}