// ***************************************************************************************************************************
// * 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.collections.JsonMap.*;
import static org.apache.juneau.common.internal.StringUtils.*;
import static org.apache.juneau.common.internal.ThrowableUtils.*;

import java.io.*;
import java.lang.annotation.*;
import java.lang.reflect.*;
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.collections.*;
import org.apache.juneau.internal.*;
import org.apache.juneau.utils.*;

/**
 * Filesystem-based storage location for configuration files.
 *
 * <p>
 * Points to a file system directory containing configuration files.
 *
 * <h5 class='section'>Notes:</h5><ul>
 *    <li class='note'>This class is thread safe and reusable.
 * </ul>
 */
public class FileStore extends ConfigStore {

   //-------------------------------------------------------------------------------------------------------------------
   // Static
   //-------------------------------------------------------------------------------------------------------------------

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

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

   //-------------------------------------------------------------------------------------------------------------------
   // Builder
   //-------------------------------------------------------------------------------------------------------------------

   /**
    * Builder class.
    */
   @FluentSetters
   public static class Builder extends ConfigStore.Builder {

      String directory, extensions;
      Charset charset;
      boolean enableWatcher, updateOnWrite;
      WatcherSensitivity watcherSensitivity;

      /**
       * Constructor, default settings.
       */
      protected Builder() {
         super();
         directory = env("ConfigFileStore.directory", ".");
         charset = env("ConfigFileStore.charset", Charset.defaultCharset());
         enableWatcher = env("ConfigFileStore.enableWatcher", false);
         watcherSensitivity = env("ConfigFileStore.watcherSensitivity", WatcherSensitivity.MEDIUM);
         updateOnWrite = env("ConfigFileStore.updateOnWrite", false);
         extensions = env("ConfigFileStore.extensions", "cfg");
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The bean to copy from.
       */
      protected Builder(FileStore copyFrom) {
         super(copyFrom);
         type(copyFrom.getClass());
         directory = copyFrom.directory;
         charset = copyFrom.charset;
         enableWatcher = copyFrom.enableWatcher;
         watcherSensitivity = copyFrom.watcherSensitivity;
         updateOnWrite = copyFrom.updateOnWrite;
         extensions = copyFrom.extensions;
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The builder to copy from.
       */
      protected Builder(Builder copyFrom) {
         super(copyFrom);
         directory = copyFrom.directory;
         charset = copyFrom.charset;
         enableWatcher = copyFrom.enableWatcher;
         watcherSensitivity = copyFrom.watcherSensitivity;
         updateOnWrite = copyFrom.updateOnWrite;
         extensions = copyFrom.extensions;
      }

      @Override /* Context.Builder */
      public Builder copy() {
         return new Builder(this);
      }

      @Override /* Context.Builder */
      public FileStore build() {
         return build(FileStore.class);
      }

      //-----------------------------------------------------------------------------------------------------------------
      // Properties
      //-----------------------------------------------------------------------------------------------------------------

      /**
       * Local file system directory.
       *
       * <p>
       * Identifies the path of the directory containing the configuration files.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.directory"
       *       <li>Environment variable <js>"CONFIGFILESTORE_DIRECTORY"
       *       <li><js>"."</js>
       *    </ul>
       * @return This object.
       */
      public Builder directory(String value) {
         directory = value;
         return this;
      }

      /**
       * Local file system directory.
       *
       * <p>
       * Identifies the path of the directory containing the configuration files.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.directory"
       *       <li>Environment variable <js>"CONFIGFILESTORE_DIRECTORY"
       *       <li><js>"."</js>.
       *    </ul>
       * @return This object.
       */
      public Builder directory(File value) {
         directory = value.getAbsolutePath();
         return this;
      }

      /**
       * Charset for external files.
       *
       * <p>
       * Identifies the charset of external files.
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.charset"
       *       <li>Environment variable <js>"CONFIGFILESTORE_CHARSET"
       *       <li>{@link Charset#defaultCharset()}
       *    </ul>
       * @return This object.
       */
      public Builder charset(Charset value) {
         charset = value;
         return this;
      }

      /**
       * Use watcher.
       *
       * <p>
       * Use a file system watcher for file system changes.
       *
       * <h5 class='section'>Notes:</h5><ul>
       *    <li class='note'>Calling {@link FileStore#close()} closes the watcher.
       * </ul>
       *
       * <p>
       *    The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.enableWatcher"
       *       <li>Environment variable <js>"CONFIGFILESTORE_ENABLEWATCHER"
       *       <li><jk>false</jk>.
       *    </ul>
       *
       * @return This object.
       */
      public Builder enableWatcher() {
         enableWatcher = true;
         return this;
      }

      /**
       * Watcher sensitivity.
       *
       * <p>
       * Determines how frequently the file system is polled for updates.
       *
       * <h5 class='section'>Notes:</h5><ul>
       *    <li class='note'>This relies on internal Sun packages and may not work on all JVMs.
       * </ul>
       *
       * @param value
       *    The new value for this property.
       *    <br>The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.watcherSensitivity"
       *       <li>Environment variable <js>"CONFIGFILESTORE_WATCHERSENSITIVITY"
       *       <li>{@link WatcherSensitivity#MEDIUM}
       *    </ul>
       * @return This object.
       */
      public Builder watcherSensitivity(WatcherSensitivity value) {
         watcherSensitivity = value;
         return this;
      }

      /**
       * Update-on-write.
       *
       * <p>
       * When enabled, the {@link FileStore#update(String, String)} method will be called immediately following
       * calls to {@link FileStore#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}.
       *
       * <p>
       *    The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.updateOnWrite"
       *       <li>Environment variable <js>"CONFIGFILESTORE_UPDATEONWRITE"
       *       <li><jk>false</jk>.
       *    </ul>
       *
       * @return This object.
       */
      public Builder updateOnWrite() {
         updateOnWrite = true;
         return this;
      }

      /**
       * File extensions.
       *
       * <p>
       * Defines what file extensions to search for when the config name does not have an extension.
       *
       * @param value
       *    The new value for this property.
       *    The default is the first value found:
       *    <ul>
       *       <li>System property <js>"ConfigFileStore.extensions"
       *       <li>Environment variable <js>"CONFIGFILESTORE_EXTENSIONS"
       *       <li><js>"cfg"</js>
       *    </ul>
       * @return This object.
       */
      public Builder extensions(String value) {
         extensions = value;
         return this;
      }

      // <FluentSetters>

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder annotations(Annotation...values) {
         super.annotations(values);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder apply(AnnotationWorkList work) {
         super.apply(work);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder applyAnnotations(java.lang.Class<?>...fromClasses) {
         super.applyAnnotations(fromClasses);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder applyAnnotations(Method...fromMethods) {
         super.applyAnnotations(fromMethods);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder cache(Cache<HashKey,? extends org.apache.juneau.Context> value) {
         super.cache(value);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder debug() {
         super.debug();
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder debug(boolean value) {
         super.debug(value);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder impl(Context value) {
         super.impl(value);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.Context.Builder */
      public Builder type(Class<? extends org.apache.juneau.Context> value) {
         super.type(value);
         return this;
      }

      // </FluentSetters>
   }

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

   @Override /* Context */
   public Builder copy() {
      return new Builder(this);
   }

   final String directory, extensions;
   final Charset charset;
   final boolean enableWatcher, updateOnWrite;
   final WatcherSensitivity watcherSensitivity;

   private final File dir;
   private final WatcherThread watcher;
   private final ConcurrentHashMap<String,String> cache = new ConcurrentHashMap<>();
   private final ConcurrentHashMap<String,String> nameCache = new ConcurrentHashMap<>();
   private final String[] exts;

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   public FileStore(Builder builder) {
      super(builder);
      directory = builder.directory;
      extensions = builder.extensions;
      charset = builder.charset;
      enableWatcher = builder.enableWatcher;
      updateOnWrite = builder.updateOnWrite;
      watcherSensitivity = builder.watcherSensitivity;
      try {
         dir = new File(directory).getCanonicalFile();
         dir.mkdirs();
         exts = split(extensions);
         watcher = enableWatcher ? new WatcherThread(dir, watcherSensitivity) : null;
         if (watcher != null)
            watcher.start();
      } catch (Exception e) {
         throw asRuntimeException(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)(((Buffer)buf).flip()))); // Fixes Java 11 issue involving overridden flip method.
               ((Buffer)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 (eq(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)((Buffer)buf).flip()));
                        ((Buffer)buf).clear();
                     }
                     currentContents = sb.toString();
                  }
                  if (expectedContents != null && ! eq(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 : exts) {
               if (FileUtils.hasExtension(name, ext)) {
                  n = name;
                  break;
               }
            }
         }

         // Find file with the correct extension.
         if (n == null) {
            for (String ext : exts) {
               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 = exts.length == 0 ? name : (name + "." + exts[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 FileStore 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);
      }

      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)
                     FileStore.this.onFileEvent(((WatchEvent<Path>)event));
               }
               if (! key.reset())
                  break;
            }
         } catch (Exception e) {
            throw asRuntimeException(e);
         }
      };

      @Override /* Thread */
      public void interrupt() {
         try {
            watchService.close();
         } catch (IOException e) {
            throw asRuntimeException(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 Thrown by underlying stream.
    */
   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 (! eq(oldContents, newContents)) {
         update(fn, newContents);
      }
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Other methods
   //-----------------------------------------------------------------------------------------------------------------

   @Override /* Context */
   protected JsonMap properties() {
      return filteredMap("charset", charset, "extensions", extensions, "updateOnWrite", updateOnWrite);
   }
}