/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

//import java.nio.file.*;
import java.nio.file.Files;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
//import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import static java.nio.file.LinkOption.*;
//import java.nio.file.attribute.*;
import java.nio.file.attribute.BasicFileAttributes;
//import java.io.*;
import java.io.IOException;
//import java.util.*;
import java.util.HashMap;
import java.util.List;
//import java.util.Map;

/**
 * Example to watch a directory (or tree) for changes to files.
 */

public class WatchDir {

  private final WatchService watcher;
  private final HashMap<WatchKey,Path> keys;

  @SuppressWarnings("unchecked")
  static <T> WatchEvent<T> cast(WatchEvent<?> event) {
    return (WatchEvent<T>)event;
  }

  /**
   * Register the given directory with the WatchService
   */
  private void register(Path dir) throws IOException {
    WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
    Path prev = keys.get(key);
    if (prev == null) {
      System.out.format("register: %s\n", dir);
    } else {
      if (!dir.equals(prev)) {
        System.out.format("update: %s -> %s\n", prev, dir);
      }
    }
    keys.put(key, dir);
  }

  /**
   * Creates a WatchService and registers the given directory
   */
  WatchDir(Path dir) throws IOException {
    this.watcher = FileSystems.getDefault().newWatchService();
    this.keys = new HashMap<WatchKey,Path>();
    register(dir);
  }

  /**
   * Process all events for keys queued to the watcher
   */
  void processEvents() {
    for (;;) {
      System.out.println("loop1");
      // wait for key to be signalled
      WatchKey key;
      try {
        key = watcher.take();
      } catch (InterruptedException x) {
        System.out.println("Interrupted");
        return;
      }

      Path dir = keys.get(key);
      if (dir == null) {
        System.err.println("WatchKey not recognized!!");
        continue;
      }

      List<WatchEvent<?>> events = key.pollEvents();
      System.out.println(events.size()); // is 0 if directory inaccessable
      for (WatchEvent<?> event: events) {
        
        WatchEvent.Kind kind = event.kind();
        System.out.println("loop2");
        // TBD - provide example of how OVERFLOW event is handled
        if (kind == OVERFLOW) {
          System.out.println("overflow");
          continue;
        }

        // Context for directory entry event is the file name of entry
        WatchEvent<Path> ev = cast(event);
        Path name = ev.context();
        Path child = dir.resolve(name);

        // print out event
        System.out.format("%s: %s\n", event.kind().name(), child);
      }

      // reset key and remove from set if directory no longer accessible
      boolean valid = key.reset();
      if (!valid) {
        System.out.println("invalid");
        keys.remove(key);
        // key.cancel();

        // all directories are inaccessible
        if (keys.isEmpty()) {
          break;
        }
      }
    }
  }

  public static void main(String[] args) throws IOException {
    if (args.length != 1) {
      System.err.println("usage: java WatchDir [-r] dir");
      System.exit(-1);
    }

    // register directory and process its events
    new WatchDir(Paths.get(args[0])).processEvents();
  }
}