/*
    * 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.commons.vfs2.provider;
  
  import java.util.Map;
  import java.util.TreeMap;
  import java.util.stream.Stream;
  
  import org.apache.commons.vfs2.FileName;
  import org.apache.commons.vfs2.FileObject;
  import org.apache.commons.vfs2.FileSystem;
  import org.apache.commons.vfs2.FileSystemConfigBuilder;
  import org.apache.commons.vfs2.FileSystemException;
  import org.apache.commons.vfs2.FileSystemOptions;
  import org.apache.commons.vfs2.provider.local.GenericFileNameParser;
  
  /**
   * A partial {@link FileProvider} implementation. Takes care of managing the file systems created by the provider.
   */
  public abstract class AbstractFileProvider extends AbstractVfsContainer implements FileProvider {
  
      private static final AbstractFileSystem[] EMPTY_ABSTRACT_FILE_SYSTEMS = {};
  
      /**
       * The cached file systems.
       * <p>
       * This is a mapping from {@link FileSystemKey} (root URI and options) to {@link FileSystem}.
       * </p>
       */
      private final Map<FileSystemKey, FileSystem> fileSystemMap = new TreeMap<>(); // @GuardedBy("self")
  
      private FileNameParser fileNameParser;
  
      /**
       * Constructs a new instance for subclasses.
       */
      public AbstractFileProvider() {
          fileNameParser = GenericFileNameParser.getInstance();
      }
  
      /**
       * Adds a file system to those cached by this provider.
       * <p>
       * The file system may implement {@link VfsComponent}, in which case it is initialized.
       * </p>
       *
       * @param key The root file of the file system, part of the cache key.
       * @param fs the file system to add.
       * @throws FileSystemException if any error occurs.
       */
      protected void addFileSystem(final Comparable<?> key, final FileSystem fs) throws FileSystemException {
          // Add to the container and initialize
          addComponent(fs);
          final FileSystemKey treeKey = new FileSystemKey(key, fs.getFileSystemOptions());
          ((AbstractFileSystem) fs).setCacheKey(treeKey);
          synchronized (fileSystemMap) {
              fileSystemMap.put(treeKey, fs);
          }
      }
  
      /**
       * Closes the file systems created by this provider.
       */
      @Override
      public void close() {
          synchronized (fileSystemMap) {
              fileSystemMap.clear();
          }
          super.close();
      }
  
      /**
       * Closes the FileSystem.
       *
       * @param fileSystem The FileSystem to close.
       */
      public void closeFileSystem(final FileSystem fileSystem) {
          final AbstractFileSystem fs = (AbstractFileSystem) fileSystem;
  
          final FileSystemKey key = fs.getCacheKey();
          if (key != null) {
              synchronized (fileSystemMap) {
                  fileSystemMap.remove(key);
              }
          }
 
         removeComponent(fs);
         fs.close();
     }
 
     /**
      * Creates a layered file system. This method throws a 'not supported' exception.
      *
      * @param scheme The protocol to use to access the file.
      * @param file a FileObject.
      * @param fileSystemOptions Options to the file system.
      * @return A FileObject associated with the new FileSystem.
      * @throws FileSystemException if an error occurs.
      */
     @Override
     public FileObject createFileSystem(final String scheme, final FileObject file,
         final FileSystemOptions fileSystemOptions) throws FileSystemException {
         // Can't create a layered file system
         throw new FileSystemException("vfs.provider/not-layered-fs.error", scheme);
     }
 
     /**
      * Locates a cached file system.
      *
      * @param key The root file of the file system, part of the cache key.
      * @param fileSystemOptions file system options the file system instance must have, may be null.
      * @return The file system instance, or null if it is not cached.
      */
     protected FileSystem findFileSystem(final Comparable<?> key, final FileSystemOptions fileSystemOptions) {
         synchronized (fileSystemMap) {
             return fileSystemMap.get(new FileSystemKey(key, fileSystemOptions));
         }
     }
 
     /**
      * Frees unused resources.
      */
     public void freeUnusedResources() {
         final AbstractFileSystem[] abstractFileSystems;
         synchronized (fileSystemMap) {
             // create snapshot under lock
             abstractFileSystems = fileSystemMap.values().toArray(EMPTY_ABSTRACT_FILE_SYSTEMS);
         }
 
         // process snapshot outside lock
         Stream.of(abstractFileSystems).filter(AbstractFileSystem::isReleaseable)
                                       .forEach(AbstractFileSystem::closeCommunicationLink);
     }
 
     /**
      * Gets the FileSystemConfigBuilder.
      *
      * @return the FileSystemConfigBuilder.
      */
     @Override
     public FileSystemConfigBuilder getConfigBuilder() {
         return null;
     }
 
     /**
      * Gets the file name parser.
      *
      * @return the file name parser.
      */
     protected FileNameParser getFileNameParser() {
         return fileNameParser;
     }
 
     /**
      * Parses an absolute URI.
      *
      * @param base The base file - if null the {@code uri} needs to be absolute
      * @param uri The URI to parse.
      * @return The FileName.
      * @throws FileSystemException if an error occurs.
      */
     @Override
     public FileName parseUri(final FileName base, final String uri) throws FileSystemException {
         if (getFileNameParser() != null) {
             return getFileNameParser().parseUri(getContext(), base, uri);
         }
         throw new FileSystemException("vfs.provider/filename-parser-missing.error");
     }
 
     /**
      * Sets the file name parser.
      *
      * @param parser a file name parser.
      */
     protected void setFileNameParser(final FileNameParser parser) {
         this.fileNameParser = parser;
     }
 }