import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;

import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import static java.nio.file.StandardWatchEventKinds.*;

public class WatchDir {
    private final WatchService watcher;
    private final Map<WatchKey, Path> keys;
    private final boolean recursive;
    private boolean trace;
    private int total = 0;

    @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, PrintWriter writer) throws IOException {
        WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
        if (trace) {
            Path prev = keys.get(key);
            if (prev == null) {
                writer.println("register:"+dir);
            } else {
                if (!dir.equals(prev)) {
                    writer.println("update.........");
                }
            }
        }
        keys.put(key, dir);
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(final Path start, PrintWriter writer){
        // register directory and sub-directories
        try{
            Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
                @Override
                public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                {
                    writer.println(++total+"Registering Path...."+dir.toUri());

                    try{
                        register(dir,writer);
                    }catch(IOException ex){
                        writer.println("Error occurred for Path..."+dir.getFileName());
                    }catch(Exception ex){
                        System.out.println("error");
                    }
                    return FileVisitResult.CONTINUE;
                }
            });
        }catch(Exception ex){
            writer.println("Not Registered ....."+ex.getMessage());
        }
    }

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

        if (recursive) {
            System.out.println("Starting Registering Path");
            writer.println("Scanning %s ...\n"+ dir);
            registerAll(dir, writer);
            writer.println("Done.");
            System.out.println("Done");
            writer.println("Total Folders in Watch "+ total);
            System.out.println("Total Folders in Watch "+ total);
        } else {
            register(dir,writer);
        }

        // enable trace after initial registration
        this.trace = true;
    }

    /**
     * Process all events for keys queued to the watcher
     * @throws UnsupportedEncodingException
     * @throws FileNotFoundException
     */
    void processEvents() throws FileNotFoundException, UnsupportedEncodingException {
        PrintWriter writer1 = new PrintWriter("C:\\test\\key.txt");
        for (;;) {

            // wait for key to be signalled
            WatchKey key;
            try {
                key = watcher.take();
                writer1.println("Folder is "+key.watchable()+" And Key is "+ key.isValid());
                System.out.println("Folder is "+key.watchable()+" And Key is "+ key.isValid());
            } catch (InterruptedException x) {
                writer1.println("Interupped Exception.........");
                return;
            }

            Path dir = keys.get(key);
            if (dir == null) {
                writer1.println("WatchKey not recognized!!");
                continue;
            }

            for (WatchEvent<?> event: key.pollEvents()) {
                WatchEvent.Kind kind = event.kind();

                // TBD - provide example of how OVERFLOW event is handled
                if (kind == OVERFLOW) {
                    writer1.println("Overflow event is caught.");
                    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);
                writer1.println("Event Kind is "+event.kind().name() +" And Name is "+child);

                // if directory is created, and watching recursively, then
                // register it and its sub-directories
                if (recursive && (kind == ENTRY_CREATE)) {
                    try {
                        if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                            registerAll(child, writer1);
                        }
                    } catch (Exception x) {
                        // ignore to keep sample readbale
                    }
                }
            }

            // reset key and remove from set if directory no longer accessible
            boolean valid = key.reset();
            if (!valid) {
                keys.remove(key);

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

    static void usage() {
        System.err.println("usage: java WatchDir [-r] dir");
        System.exit(-1);
    }

    public static void main(String[] args) throws IOException {
        // register directory and process its events
        PrintWriter writer = new PrintWriter("C:\\test\\watch.txt");
        Path dir = Paths.get("\\\\10.168.69.77\\Shared\\test\\");
        new WatchDir(dir, true,writer).processEvents();
    }
}