// ***************************************************************************************************************************
// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
// * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance            *
// * with the License.  You may obtain a copy of the License at                                                              *
// *                                                                                                                         *
// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
// *                                                                                                                         *
// * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an  *
// * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the License for the        *
// * specific language governing permissions and limitations under the License.                                              *
// ***************************************************************************************************************************
package org.apache.juneau.config.store;

import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.StandardOpenOption.*;
import static org.apache.juneau.internal.StringUtils.*;

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.nio.file.*;
import java.util.concurrent.*;

import org.apache.juneau.*;
import org.apache.juneau.internal.*;

/**
 * Filesystem-based storage location for configuration files.
 *
 * <p>
 * Points to a file system directory containing configuration files.
 */
public class ConfigFileStore extends ConfigStore {

   //-------------------------------------------------------------------------------------------------------------------
   // Configurable properties
   //-------------------------------------------------------------------------------------------------------------------

   private static final String PREFIX = "ConfigFileStore.";

   /**
    * Configuration property:  Local file system directory.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.directory.s"</js>
    *    <li><b>Data type:</b>  <code>String</code>
    *    <li><b>Default:</b>  <js>"."</js>
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#directory(String)}
    *          <li class='jm'>{@link ConfigFileStoreBuilder#directory(File)}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * Identifies the path of the directory containing the configuration files.
    */
   public static final String FILESTORE_directory = PREFIX + "directory.s";

   /**
    * Configuration property:  Charset.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.charset.s"</js>
    *    <li><b>Data type:</b>  {@link Charset}
    *    <li><b>Default:</b>  {@link Charset#defaultCharset()}
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#charset(String)}
    *          <li class='jm'>{@link ConfigFileStoreBuilder#charset(Charset)}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * Identifies the charset of external files.
    */
   public static final String FILESTORE_charset = PREFIX + "charset.s";

   /**
    * Configuration property:  Use watcher.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.useWatcher.b"</js>
    *    <li><b>Data type:</b>  <code>Boolean</code>
    *    <li><b>Default:</b>  <jk>false</jk>
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#useWatcher()}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * Use a file system watcher for file system changes.
    *
    * <h5 class='section'>Notes:</h5>
    * <ul class='spaced-list'>
    *    <li>Calling {@link #close()} on this object closes the watcher.
    * </ul>
    */
   public static final String FILESTORE_useWatcher = PREFIX + "useWatcher.s";

   /**
    * Configuration property:  Watcher sensitivity.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.watcherSensitivity.s"</js>
    *    <li><b>Data type:</b>  {@link WatcherSensitivity}
    *    <li><b>Default:</b>  {@link WatcherSensitivity#MEDIUM}
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#watcherSensitivity(WatcherSensitivity)}
    *          <li class='jm'>{@link ConfigFileStoreBuilder#watcherSensitivity(String)}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * Determines how frequently the file system is polled for updates.
    *
    * <h5 class='section'>Notes:</h5>
    * <ul class='spaced-list'>
    *    <li>This relies on internal Sun packages and may not work on all JVMs.
    * </ul>
    */
   public static final String FILESTORE_watcherSensitivity = PREFIX + "watcherSensitivity.s";

   /**
    * Configuration property:  Update-on-write.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.updateOnWrite.b"</js>
    *    <li><b>Data type:</b>  <code>Boolean</code>
    *    <li><b>Default:</b>  <jk>false</jk>
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#updateOnWrite()}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * When enabled, the {@link #update(String, String)} method will be called immediately following
    * calls to {@link #write(String, String, String)} when the contents are changing.
    * <br>This allows for more immediate responses to configuration changes on file systems that use
    * polling watchers.
    * <br>This may cause double-triggering of {@link ConfigStoreListener ConfigStoreListeners}.
    */
   public static final String FILESTORE_updateOnWrite = PREFIX + "updateOnWrite.b";

   /**
    * Configuration property:  File extensions.
    *
    * <h5 class='section'>Property:</h5>
    * <ul>
    *    <li><b>Name:</b>  <js>"ConfigFileStore.extensions.ls"</js>
    *    <li><b>Data type:</b>  <code>String[]</code>
    *    <li><b>Default:</b>  <jk>"cfg"</jk>
    *    <li><b>Methods:</b>
    *       <ul>
    *          <li class='jm'>{@link ConfigFileStoreBuilder#extensions(String...)}
    *       </ul>
    * </ul>
    *
    * <h5 class='section'>Description:</h5>
    * <p>
    * Defines what file extensions to search for when the config name does not have an extension.
    */
   public static final String FILESTORE_extensions = PREFIX + "extensions.ls";

   //-------------------------------------------------------------------------------------------------------------------
   // Predefined instances
   //-------------------------------------------------------------------------------------------------------------------

   /** Default file store, all default values.*/
   public static final ConfigFileStore DEFAULT = ConfigFileStore.create().build();


   //-------------------------------------------------------------------------------------------------------------------
   // Instance
   //-------------------------------------------------------------------------------------------------------------------

   /**
    * Create a new builder for this object.
    *
    * @return A new builder for this object.
    */
   public static ConfigFileStoreBuilder create() {
      return new ConfigFileStoreBuilder();
   }

   @Override /* Context */
   public ConfigFileStoreBuilder builder() {
      return new ConfigFileStoreBuilder(getPropertyStore());
   }

   private final File dir;
   private final Charset charset;
   private final WatcherThread watcher;
   private final boolean updateOnWrite;
   private final ConcurrentHashMap<String,String> cache = new ConcurrentHashMap<>();
   private final ConcurrentHashMap<String,String> nameCache = new ConcurrentHashMap<>();
   private final String[] extensions;

   /**
    * Constructor.
    *
    * @param ps The settings for this content store.
    */
   protected ConfigFileStore(PropertyStore ps) {
      super(ps);
      try {
         dir = new File(getStringProperty(FILESTORE_directory, ".")).getCanonicalFile();
         dir.mkdirs();
         charset = getProperty(FILESTORE_charset, Charset.class, Charset.defaultCharset());
         updateOnWrite = getBooleanProperty(FILESTORE_updateOnWrite, false);
         extensions = getArrayProperty(FILESTORE_extensions, String.class, new String[]{"cfg"});
         WatcherSensitivity ws = getProperty(FILESTORE_watcherSensitivity, WatcherSensitivity.class, WatcherSensitivity.MEDIUM);
         watcher = getBooleanProperty(FILESTORE_useWatcher, false) ? new WatcherThread(dir, ws) : null;
         if (watcher != null)
            watcher.start();

      } catch (Exception e) {
         throw new RuntimeException(e);
      }
   }

   @Override /* ConfigStore */
   public synchronized String read(String name) throws IOException {
      name = resolveName(name);

      Path p = resolveFile(name);
      name = p.getFileName().toString();

      String s = cache.get(name);
      if (s != null)
         return s;

      dir.mkdirs();

      // If file doesn't exist, don't trigger creation.
      if (! Files.exists(p))
         return "";

      boolean isWritable = isWritable(p);
      OpenOption[] oo = isWritable ? new OpenOption[]{READ,WRITE,CREATE} : new OpenOption[]{READ};

      try (FileChannel fc = FileChannel.open(p, oo)) {
         try (FileLock lock = isWritable ? fc.lock() : null) {
            ByteBuffer buf = ByteBuffer.allocate(1024);
            StringBuilder sb = new StringBuilder();
            while (fc.read(buf) != -1) {
               sb.append(charset.decode((ByteBuffer)(buf.flip())));
               buf.clear();
            }
            s = sb.toString();
            cache.put(name, s);
         }
      }

      return cache.get(name);
   }

   @Override /* ConfigStore */
   public synchronized String write(String name, String expectedContents, String newContents) throws IOException {
      name = resolveName(name);

      // This is a no-op.
      if (isEquals(expectedContents, newContents))
         return null;

      dir.mkdirs();

      Path p = resolveFile(name);
      name = p.getFileName().toString();

      boolean exists = Files.exists(p);

      // Don't create the file if we're not going to match.
      if ((!exists) && isNotEmpty(expectedContents))
         return "";

      if (isWritable(p)) {
         if (newContents == null)
            Files.delete(p);
         else {
            try (FileChannel fc = FileChannel.open(p, READ, WRITE, CREATE)) {
               try (FileLock lock = fc.lock()) {
                  String currentContents = "";
                  if (exists) {
                     ByteBuffer buf = ByteBuffer.allocate(1024);
                     StringBuilder sb = new StringBuilder();
                     while (fc.read(buf) != -1) {
                        sb.append(charset.decode((ByteBuffer)(buf.flip())));
                        buf.clear();
                     }
                     currentContents = sb.toString();
                  }
                  if (expectedContents != null && ! isEquals(currentContents, expectedContents)) {
                     if (currentContents == null)
                        cache.remove(name);
                     else
                        cache.put(name, currentContents);
                     return currentContents;
                  }
                  fc.position(0);
                  fc.write(charset.encode(newContents));
               }
            }
         }
      }

      if (updateOnWrite)
         update(name, newContents);
      else
         cache.remove(name);  // Invalidate the cache.

      return null;
   }

   @Override /* ConfigStore */
   public synchronized boolean exists(String name) {
      return Files.exists(resolveFile(name));
   }

   private Path resolveFile(String name) {
      return dir.toPath().resolve(resolveName(name));
   }

   @Override
   protected String resolveName(String name) {
      if (! nameCache.containsKey(name)) {
         String n = null;

         // Does file exist as-is?
         if (FileUtils.exists(dir, name))
            n = name;

         // Does name already have an extension?
         if (n == null) {
            for (String ext : extensions) {
               if (FileUtils.hasExtension(name, ext)) {
                  n = name;
                  break;
               }
            }
         }

         // Find file with the correct extension.
         if (n == null) {
            for (String ext : extensions) {
               if (FileUtils.exists(dir, name + '.' + ext)) {
                  n = name + '.' + ext;
                  break;
               }
            }
         }

         // If file not found, use the default which is the name with the first extension.
         if (n == null)
            n = extensions.length == 0 ? name : (name + "." + extensions[0]);

         nameCache.put(name, n);
      }
      return nameCache.get(name);
   }

   private synchronized boolean isWritable(Path p) {
      try {
         if (! Files.exists(p)) {
            Files.createDirectories(p.getParent());
            if (! Files.exists(p))
               p.toFile().createNewFile();
         }
      } catch (IOException e) {
         return false;
      }
      return Files.isWritable(p);
   }

   @Override /* ConfigStore */
   public synchronized ConfigFileStore update(String name, String newContents) {
      cache.put(name, newContents);
      super.update(name, newContents);
      return this;
   }

   @Override /* Closeable */
   public synchronized void close() {
      if (watcher != null)
         watcher.interrupt();
   }


   //---------------------------------------------------------------------------------------------
   // WatcherThread
   //---------------------------------------------------------------------------------------------

   final class WatcherThread extends Thread {
      private final WatchService watchService;

      WatcherThread(File dir, WatcherSensitivity s) throws Exception {
         watchService = FileSystems.getDefault().newWatchService();
         WatchEvent.Kind<?>[] kinds = new WatchEvent.Kind[]{ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY};
         WatchEvent.Modifier modifier = lookupModifier(s);
         dir.toPath().register(watchService, kinds, modifier);
      }

      @SuppressWarnings("restriction")
      private WatchEvent.Modifier lookupModifier(WatcherSensitivity s) {
         try {
            switch(s) {
               case LOW: return com.sun.nio.file.SensitivityWatchEventModifier.LOW;
               case MEDIUM: return com.sun.nio.file.SensitivityWatchEventModifier.MEDIUM;
               case HIGH: return com.sun.nio.file.SensitivityWatchEventModifier.HIGH;
            }
         } catch (Exception e) {
            /* Ignore */
         }
         return null;

      }

      @SuppressWarnings("unchecked")
      @Override /* Thread */
      public void run() {
          try {
            WatchKey key;
            while ((key = watchService.take()) != null) {
                for (WatchEvent<?> event : key.pollEvents()) {
                    WatchEvent.Kind<?> kind = event.kind();
                    if (kind != OVERFLOW)
                        ConfigFileStore.this.onFileEvent(((WatchEvent<Path>)event));
                }
                if (! key.reset())
                     break;
            }
         } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
         }
      };

      @Override /* Thread */
      public void interrupt() {
         try {
            watchService.close();
         } catch (IOException e) {
            throw new RuntimeException(e);
         } finally {
            super.interrupt();
         }
      }
   }

   /**
    * Gets called when the watcher service on this store is triggered with a file system change.
    *
    * @param e The file system event.
    * @throws IOException
    */
   protected synchronized void onFileEvent(WatchEvent<Path> e) throws IOException {
      String fn = e.context().getFileName().toString();

      String oldContents = cache.get(fn);
      cache.remove(fn);
      String newContents = read(fn);
      if (! isEquals(oldContents, newContents)) {
         update(fn, newContents);
      }
   }
}