/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package sun.nio.fs;

import java.nio.file.*;

import java.nio.file.attribute.*;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.security.PrivilegedExceptionAction;

import java.security.PrivilegedActionException;

import java.io.IOException;

import java.util.*;

import java.util.concurrent.*;

import com.sun.nio.file.SensitivityWatchEventModifier;

/**

 * Simple WatchService implementation that uses periodic tasks to poll

 * registered directories for changes.  This implementation is for use on

 * operating systems that do not have native file change notification support.

 */

class PollingWatchService

    extends AbstractWatchService

{

    // map of registrations

    private final Map<Object,PollingWatchKey> map =

        new HashMap<Object,PollingWatchKey>();

    // used to execute the periodic tasks that poll for changes

    private final ScheduledExecutorService scheduledExecutor;

    PollingWatchService() {

        // TBD: Make the number of threads configurable

        scheduledExecutor = Executors

            .newSingleThreadScheduledExecutor(new ThreadFactory() {

                 @Override

                 public Thread newThread(Runnable r) {

                     Thread t = new Thread(r);

                     t.setDaemon(true);

                     return t;

                 }});

    }

    /**

     * Register the given file with this watch service

     */

    @Override

    WatchKey register(final Path path,

                      WatchEvent.Kind<?>[] events,

                      WatchEvent.Modifier... modifiers)

         throws IOException

    {

        // check events - CCE will be thrown if there are invalid elements

        if (events.length == 0)

            throw new IllegalArgumentException("No events to register");

        final Set<WatchEvent.Kind<?>> eventSet =

            new HashSet<WatchEvent.Kind<?>>(events.length);

        for (WatchEvent.Kind<?> event: events) {

            // standard events

            if (event == StandardWatchEventKind.ENTRY_CREATE ||

                event == StandardWatchEventKind.ENTRY_MODIFY ||

                event == StandardWatchEventKind.ENTRY_DELETE)

            {

                eventSet.add(event);

                continue;

            }

            // OVERFLOW is ignored

            if (event == StandardWatchEventKind.OVERFLOW) {

                if (events.length == 1)

                    throw new IllegalArgumentException("No events to register");

                continue;

            }

            // null/unsupported

            if (event == null)

                throw new NullPointerException("An element in event set is 'null'");

            throw new UnsupportedOperationException(event.name());

        }

        // A modifier may be used to specify the sensitivity level

        SensitivityWatchEventModifier sensivity = SensitivityWatchEventModifier.MEDIUM;

        if (modifiers.length > 0) {

            for (WatchEvent.Modifier modifier: modifiers) {

                if (modifier == null)

                    throw new NullPointerException();

                if (modifier instanceof SensitivityWatchEventModifier) {

                    sensivity = (SensitivityWatchEventModifier)modifier;

                    continue;

                }

                throw new UnsupportedOperationException("Modifier not supported");

            }

        }

        // check if watch service is closed

        if (!isOpen())

            throw new ClosedWatchServiceException();

        // registration is done in privileged block as it requires the

        // attributes of the entries in the directory.

        try {

            final SensitivityWatchEventModifier s = sensivity;

            return AccessController.doPrivileged(

                new PrivilegedExceptionAction<PollingWatchKey>() {

                    @Override

                    public PollingWatchKey run() throws IOException {

                        return doPrivilegedRegister(path, eventSet, s);

                    }

                });

        } catch (PrivilegedActionException pae) {

            Throwable cause = pae.getCause();

            if (cause != null && cause instanceof IOException)

                throw (IOException)cause;

            throw new AssertionError(pae);

        }

    }

    // registers directory returning a new key if not already registered or

    // existing key if already registered

    private PollingWatchKey doPrivilegedRegister(Path path,

                                                 Set<? extends WatchEvent.Kind<?>> events,

                                                 SensitivityWatchEventModifier sensivity)

        throws IOException

    {

        // check file is a directory and get its file key if possible

        BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class);

        if (!attrs.isDirectory()) {

            throw new NotDirectoryException(path.toString());

        }

        Object fileKey = attrs.fileKey();

        if (fileKey == null)

            throw new AssertionError("File keys must be supported");

        // grab close lock to ensure that watch service cannot be closed

        synchronized (closeLock()) {

            if (!isOpen())

                throw new ClosedWatchServiceException();

            PollingWatchKey watchKey;

            synchronized (map) {

                watchKey = map.get(fileKey);

                if (watchKey == null) {

                    // new registration

                    watchKey = new PollingWatchKey(path, this, fileKey);

                    map.put(fileKey, watchKey);

                } else {

                    // update to existing registration

                    watchKey.disable();

                }

            }

            watchKey.enable(events, sensivity.sensitivityValueInSeconds());

            return watchKey;

        }

    }

    @Override

    void implClose() throws IOException {

        synchronized (map) {

            for (Map.Entry<Object,PollingWatchKey> entry: map.entrySet()) {

                PollingWatchKey watchKey = entry.getValue();

                watchKey.disable();

                watchKey.invalidate();

            }

            map.clear();

        }

        AccessController.doPrivileged(new PrivilegedAction<Void>() {

            @Override

            public Void run() {

                scheduledExecutor.shutdown();

                return null;

            }

         });

    }

    /**

     * Entry in directory cache to record file last-modified-time and tick-count

     */

    private static class CacheEntry {

        private long lastModified;

        private int lastTickCount;

        CacheEntry(long lastModified, int lastTickCount) {

            this.lastModified = lastModified;

            this.lastTickCount = lastTickCount;

        }

        int lastTickCount() {

            return lastTickCount;

        }

        long lastModified() {

            return lastModified;

        }

        void update(long lastModified, int tickCount) {

            this.lastModified = lastModified;

            this.lastTickCount = tickCount;

        }

    }

    /**

     * WatchKey implementation that encapsulates a map of the entries of the

     * entries in the directory. Polling the key causes it to re-scan the

     * directory and queue keys when entries are added, modified, or deleted.

     */

    private class PollingWatchKey extends AbstractWatchKey {

        private final Object fileKey;

        // current event set

        private Set<? extends WatchEvent.Kind<?>> events;

        // the result of the periodic task that causes this key to be polled

        private ScheduledFuture<?> poller;

        // indicates if the key is valid

        private volatile boolean valid;

        // used to detect files that have been deleted

        private int tickCount;

        // map of entries in directory

        private Map<Path,CacheEntry> entries;

        PollingWatchKey(Path dir, PollingWatchService watcher, Object fileKey)

            throws IOException

        {

            super(dir, watcher);

            this.fileKey = fileKey;

            this.valid = true;

            this.tickCount = 0;

            this.entries = new HashMap<Path,CacheEntry>();

            // get the initial entries in the directory

            try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {

                for (Path entry: stream) {

                    // don't follow links

                    long lastModified =

                        Files.getLastModifiedTime(entry, LinkOption.NOFOLLOW_LINKS).toMillis();

                    entries.put(entry.getFileName(), new CacheEntry(lastModified, tickCount));

                }

            } catch (DirectoryIteratorException e) {

                throw e.getCause();

            }

        }

        Object fileKey() {

            return fileKey;

        }

        @Override

        public boolean isValid() {

            return valid;

        }

        void invalidate() {

            valid = false;

        }

        // enables periodic polling

        void enable(Set<? extends WatchEvent.Kind<?>> events, long period) {

            synchronized (this) {

                // update the events

                this.events = events;

                // create the periodic task

                Runnable thunk = new Runnable() { public void run() { poll(); }};

                this.poller = scheduledExecutor

                    .scheduleAtFixedRate(thunk, period, period, TimeUnit.SECONDS);

            }

        }

        // disables periodic polling

        void disable() {

            synchronized (this) {

                if (poller != null)

                    poller.cancel(false);

            }

        }

        @Override

        public void cancel() {

            valid = false;

            synchronized (map) {

                map.remove(fileKey());

            }

            disable();

        }

        /**

         * Polls the directory to detect for new files, modified files, or

         * deleted files.

         */

        synchronized void poll() {

            if (!valid) {

                return;

            }

            // update tick

            tickCount++;

            // open directory

            DirectoryStream<Path> stream = null;

            try {

                stream = Files.newDirectoryStream(watchable());

            } catch (IOException x) {

                // directory is no longer accessible so cancel key

                cancel();

                signal();

                return;

            }

            // iterate over all entries in directory

            try {

                for (Path entry: stream) {

                    long lastModified = 0L;

                    try {

                        lastModified =

                            Files.getLastModifiedTime(entry, LinkOption.NOFOLLOW_LINKS).toMillis();

                    } catch (IOException x) {

                        // unable to get attributes of entry. If file has just

                        // been deleted then we'll report it as deleted on the

                        // next poll

                        continue;

                    }

                    // lookup cache

                    CacheEntry e = entries.get(entry.getFileName());

                    if (e == null) {

                        // new file found

                        entries.put(entry.getFileName(),

                                     new CacheEntry(lastModified, tickCount));

                        // queue ENTRY_CREATE if event enabled

                        if (events.contains(StandardWatchEventKind.ENTRY_CREATE)) {

                            signalEvent(StandardWatchEventKind.ENTRY_CREATE, entry.getFileName());

                            continue;

                        } else {

                            // if ENTRY_CREATE is not enabled and ENTRY_MODIFY is

                            // enabled then queue event to avoid missing out on

                            // modifications to the file immediately after it is

                            // created.

                            if (events.contains(StandardWatchEventKind.ENTRY_MODIFY)) {

                                signalEvent(StandardWatchEventKind.ENTRY_MODIFY, entry.getFileName());

                            }

                        }

                        continue;

                    }

                    // check if file has changed

                    if (e.lastModified != lastModified) {

                        if (events.contains(StandardWatchEventKind.ENTRY_MODIFY)) {

                            signalEvent(StandardWatchEventKind.ENTRY_MODIFY,

                                        entry.getFileName());

                        }

                    }

                    // entry in cache so update poll time

                    e.update(lastModified, tickCount);

                }

            } catch (DirectoryIteratorException e) {

                // ignore for now; if the directory is no longer accessible

                // then the key will be cancelled on the next poll

            } finally {

                // close directory stream

                try {

                    stream.close();

                } catch (IOException x) {

                    // ignore

                }

            }

            // iterate over cache to detect entries that have been deleted

            Iterator<Map.Entry<Path,CacheEntry>> i = entries.entrySet().iterator();

            while (i.hasNext()) {

                Map.Entry<Path,CacheEntry> mapEntry = i.next();

                CacheEntry entry = mapEntry.getValue();

                if (entry.lastTickCount() != tickCount) {

                    Path name = mapEntry.getKey();

                    // remove from map and queue delete event (if enabled)

                    i.remove();

                    if (events.contains(StandardWatchEventKind.ENTRY_DELETE)) {

                        signalEvent(StandardWatchEventKind.ENTRY_DELETE, name);

                    }

                }

            }

        }

    }

}