/*
 * 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.io.File;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.commons.vfs2.CacheStrategy;
import org.apache.commons.vfs2.Capability;
import org.apache.commons.vfs2.FileListener;
import org.apache.commons.vfs2.FileName;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSelector;
import org.apache.commons.vfs2.FileSystem;
import org.apache.commons.vfs2.FileSystemConfigBuilder;
import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.FileSystemManager;
import org.apache.commons.vfs2.FileSystemOptions;
import org.apache.commons.vfs2.FilesCache;
import org.apache.commons.vfs2.VfsLog;
import org.apache.commons.vfs2.cache.OnCallRefreshFileObject;
import org.apache.commons.vfs2.events.AbstractFileChangeEvent;
import org.apache.commons.vfs2.events.ChangedEvent;
import org.apache.commons.vfs2.events.CreateEvent;
import org.apache.commons.vfs2.events.DeleteEvent;
import org.apache.commons.vfs2.impl.DefaultFileSystemConfigBuilder;
import org.apache.commons.vfs2.util.FileObjectUtils;
import org.apache.commons.vfs2.util.Messages;

/**
 * A partial {@link org.apache.commons.vfs2.FileSystem} implementation.
 */
public abstract class AbstractFileSystem extends AbstractVfsComponent implements FileSystem {

    private static final FileListener[] EMPTY_FILE_LISTENER_ARRAY = {};

    private static final Log LOG = LogFactory.getLog(AbstractFileSystem.class);

    /**
     * The "root" of the file system. This is always "/" so it isn't always the "real" root.
     */
    private final FileName rootName;

    /**
     * The root URI of the file system. The base path specified as a file system option when the file system was
     * created.
     */
    private final String rootURI;

    private final Collection<Capability> capabilities = new HashSet<>();

    private final FileObject parentLayer;

    /**
     * Map from FileName to an ArrayList of listeners for that file.
     */
    private final Map<FileName, ArrayList<FileListener>> listenerMap = new HashMap<>();

    /**
     * FileSystemOptions used for configuration
     */
    private final FileSystemOptions fileSystemOptions;

    /**
     * How many fileObjects are handed out
     */
    private final AtomicLong useCount = new AtomicLong();

    private FileSystemKey cacheKey;

    /**
     * open streams counter for this file system
     */
    private final AtomicInteger openStreams = new AtomicInteger(0);

    /** Only provided for Serializable subclasses. */
    AbstractFileSystem() {
        this(null, null, null);
    }

    /**
     * Constructs a new instance.
     *
     * @param rootFileName The root file name of this file system.
     * @param parentLayer The parent layer of this file system.
     * @param fileSystemOptions Options to build this file system.
     */
    protected AbstractFileSystem(final FileName rootFileName, final FileObject parentLayer, final FileSystemOptions fileSystemOptions) {
        this.parentLayer = parentLayer;
        this.rootName = rootFileName;
        this.fileSystemOptions = fileSystemOptions;
        final FileSystemConfigBuilder builder = DefaultFileSystemConfigBuilder.getInstance();
        String uri = builder.getRootURI(fileSystemOptions);
        if (uri == null) {
            uri = rootFileName != null ? rootFileName.getURI() : null;
        }
        this.rootURI = uri;
    }

    /**
     * Adds the capabilities of this file system.
     *
     * @param caps collections of Capabilities, can be immutable.
     */
    protected abstract void addCapabilities(Collection<Capability> caps);

    /**
     * Adds a junction to this file system.
     *
     * @param junctionPoint The junction point.
     * @param targetFile The target to add.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public void addJunction(final String junctionPoint, final FileObject targetFile) throws FileSystemException {
        throw new FileSystemException("vfs.provider/junctions-not-supported.error", rootName);
    }

    /**
     * Adds a listener on a file in this file system.
     *
     * @param file The FileObject to be monitored.
     * @param listener The FileListener
     */
    @Override
    public void addListener(final FileObject file, final FileListener listener) {
        synchronized (listenerMap) {
            final ArrayList<FileListener> listeners = listenerMap.computeIfAbsent(file.getName(), k -> new ArrayList<>());
            listeners.add(listener);
        }
    }

    /**
     * Closes this component.
     */
    @Override
    public void close() {
        closeCommunicationLink();
    }

    /**
     * Closes the underlying link used to access the files.
     */
    public void closeCommunicationLink() {
        synchronized (this) {
            doCloseCommunicationLink();
        }
    }

    /**
     * Creates a file object.
     * <p>
     * This method is called only if the requested file is not cached.
     * </p>
     *
     * @param name name referencing the new file.
     * @return new created FileObject.
     * @throws Exception might throw an Exception, which is then wrapped in FileSystemException.
     */
    protected abstract FileObject createFile(AbstractFileName name) throws Exception;

    protected FileObject decorateFileObject(FileObject file) throws FileSystemException {
        if (getFileSystemManager().getCacheStrategy().equals(CacheStrategy.ON_CALL)) {
            file = new OnCallRefreshFileObject(file);
        }

        if (getFileSystemManager().getFileObjectDecoratorConst() != null) {
            try {
                file = (FileObject) getFileSystemManager().getFileObjectDecoratorConst().newInstance(file);
            } catch (final InstantiationException | IllegalAccessException | InvocationTargetException e) {
                throw new FileSystemException("vfs.impl/invalid-decorator.error",
                        getFileSystemManager().getFileObjectDecorator().getName(), e);
            }
        }

        return file;
    }

    /**
     * Closes the underlying link used to access the files.
     */
    protected void doCloseCommunicationLink() {
        // default is noop.
    }

    /**
     * Creates a temporary local copy of a file and its descendants.
     *
     * @param file the start of the tree.
     * @param selector selection what to do with children.
     * @return replicated root file.
     * @throws Exception any Exception is wrapped as FileSystemException.
     */
    protected File doReplicateFile(final FileObject file, final FileSelector selector) throws Exception {
        return getContext().getReplicator().replicateFile(file, selector);
    }

    void fileObjectDestroyed(final FileObject fileObject) {
        useCount.decrementAndGet();
    }

    void fileObjectHanded(final FileObject fileObject) {
        useCount.incrementAndGet();
    }

    /**
     * Fires an event.
     */
    private void fireEvent(final AbstractFileChangeEvent event) {
        FileListener[] fileListeners = null;
        final FileObject fileObject = event.getFileObject();

        synchronized (listenerMap) {
            final ArrayList<?> listeners = listenerMap.get(fileObject.getName());
            if (listeners != null) {
                fileListeners = listeners.toArray(EMPTY_FILE_LISTENER_ARRAY);
            }
        }

        if (fileListeners != null) {
            for (final FileListener fileListener : fileListeners) {
                try {
                    event.notify(fileListener);
                } catch (final Exception e) {
                    final String message = Messages.getString("vfs.provider/notify-listener.warn", fileObject);
                    // getLogger().warn(message, e);
                    VfsLog.warn(getLogger(), LOG, message, e);
                }
            }
        }
    }

    /**
     * Fires a file changed event.
     * <p>
     * This will only happen if you monitor the file using {@link org.apache.commons.vfs2.FileMonitor}.
     * </p>
     *
     * @param file The FileObject that changed.
     */
    public void fireFileChanged(final FileObject file) {
        fireEvent(new ChangedEvent(file));
    }

    /**
     * Fires a file create event.
     *
     * @param file The FileObject that was created.
     */
    public void fireFileCreated(final FileObject file) {
        fireEvent(new CreateEvent(file));
    }

    /**
     * Fires a file delete event.
     *
     * @param file The FileObject that was deleted.
     */
    public void fireFileDeleted(final FileObject file) {
        fireEvent(new DeleteEvent(file));
    }

    void freeResources() {
        // default is noop.
    }

    /**
     * Retrieves the attribute with the specified name. The default implementation simply throws an exception.
     *
     * @param attrName The name of the attribute.
     * @return the Object associated with the attribute or null if no object is.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public Object getAttribute(final String attrName) throws FileSystemException {
        throw new FileSystemException("vfs.provider/get-attribute-not-supported.error");
    }

    FileSystemKey getCacheKey() {
        return this.cacheKey;
    }

    /**
     * Returns a cached file.
     *
     * @param name name to search for.
     * @return file object or null if not found.
     */
    protected FileObject getFileFromCache(final FileName name) {
        return getFilesCache().getFile(this, name);
    }

    private FilesCache getFilesCache() {
        final FilesCache filesCache = getContext().getFileSystemManager().getFilesCache();
        return Objects.requireNonNull(filesCache, () -> Messages.getString("vfs.provider/files-cache-missing.error"));
    }

    /**
     * Returns the FileSystemManager used to instantiate this file system.
     *
     * @return the FileSystemManager.
     */
    @Override
    public FileSystemManager getFileSystemManager() {
        return getContext().getFileSystemManager();
    }

    /**
     * Returns the FileSystemOptions used to instantiate this file system.
     *
     * @return the FileSystemOptions.
     */
    @Override
    public FileSystemOptions getFileSystemOptions() {
        return fileSystemOptions;
    }

    /**
     * Returns the accuracy of the last modification time.
     *
     * @return ms 0 perfectly accurate, {@literal >0} might be off by this value e.g. sftp 1000ms
     */
    @Override
    public double getLastModTimeAccuracy() {
        return 0;
    }

    /**
     * Returns the parent layer if this is a layered file system.
     *
     * @return The FileObject for the parent layer.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public FileObject getParentLayer() throws FileSystemException {
        return parentLayer;
    }

    /**
     * Returns the root file of this file system.
     *
     * @return The root FileObject of the FileSystem
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public FileObject getRoot() throws FileSystemException {
        return resolveFile(rootName);
    }

    /**
     * Returns the name of the root of this file system.
     *
     * @return the root FileName.
     */
    @Override
    public FileName getRootName() {
        return rootName;
    }

    /**
     * Returns the root URI specified for this file System.
     *
     * @return The root URI used in this file system.
     * @since 2.0
     */
    @Override
    public String getRootURI() {
        return rootURI;
    }

    /**
     * Determines if this file system has a particular capability.
     *
     * @param capability the Capability to check for.
     * @return true if the FileSystem has the Capability, false otherwise.
     */
    @Override
    public boolean hasCapability(final Capability capability) {
        return capabilities.contains(capability);
    }

    /**
     * Initializes this component.
     *
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public void init() throws FileSystemException {
        addCapabilities(capabilities);
    }

    /**
     * Checks if this file system has open streams.
     *
     * @return true if the FileSystem has open streams.
     */
    public boolean isOpen() {
        return openStreams.get() > 0;
    }

    /**
     * Returns true if no file is using this FileSystem.
     *
     * @return true if no file is using this FileSystem.
     */
    public boolean isReleaseable() {
        return useCount.get() < 1;
    }

    /**
     * Called after all file-objects closed their streams.
     */
    protected void notifyAllStreamsClosed() {
        // default is noop.
    }

    /**
     * Adds a file object to the cache.
     *
     * @param file the file to add.
     */
    protected void putFileToCache(final FileObject file) {
        getFilesCache().putFile(file);
    }

    /**
     * Removes a cached file.
     *
     * @param name The file name to remove.
     */
    protected void removeFileFromCache(final FileName name) {
        getFilesCache().removeFile(this, name);
    }

    /**
     * Removes a junction from this file system.
     *
     * @param junctionPoint The junction point.
     * @throws FileSystemException if an error occurs
     */
    @Override
    public void removeJunction(final String junctionPoint) throws FileSystemException {
        throw new FileSystemException("vfs.provider/junctions-not-supported.error", rootName);
    }

    /**
     * Removes a listener from a file in this file system.
     *
     * @param file The FileObject to be monitored.
     * @param listener The FileListener
     */
    @Override
    public void removeListener(final FileObject file, final FileListener listener) {
        synchronized (listenerMap) {
            final ArrayList<?> listeners = listenerMap.get(file.getName());
            if (listeners != null) {
                listeners.remove(listener);
                if (listeners.isEmpty()) {
                    listenerMap.remove(file.getName());
                }
            }
        }
    }

    /**
     * Creates a temporary local copy of a file and its descendants.
     *
     * @param file The FileObject to replicate.
     * @param selector The FileSelector.
     * @return The replicated File.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public File replicateFile(final FileObject file, final FileSelector selector) throws FileSystemException {
        if (!FileObjectUtils.exists(file)) {
            throw new FileSystemException("vfs.provider/replicate-missing-file.error", file.getName());
        }

        try {
            return doReplicateFile(file, selector);
        } catch (final Exception e) {
            throw new FileSystemException("vfs.provider/replicate-file.error", file.getName(), e);
        }
    }

    /**
     * Finds a file in this file system.
     *
     * @param name The name of the file to locate.
     * @return The located FileObject or null if none could be located.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public FileObject resolveFile(final FileName name) throws FileSystemException {
        return resolveFile(name, true);
    }

    private synchronized FileObject resolveFile(final FileName name, final boolean useCache)
            throws FileSystemException {
        if (!rootName.getRootURI().equals(name.getRootURI())) {
            throw new FileSystemException("vfs.provider/mismatched-fs-for-name.error", name, rootName,
                    name.getRootURI());
        }

        // imario@apache.org ==> use getFileFromCache
        FileObject file;
        if (useCache) {
            file = getFileFromCache(name);
        } else {
            file = null;
        }

        if (file == null) {
            try {
                file = createFile((AbstractFileName) name);
            } catch (final Exception e) {
                throw new FileSystemException("vfs.provider/resolve-file.error", name, e);
            }

            file = decorateFileObject(file);

            // imario@apache.org ==> use putFileToCache
            if (useCache) {
                putFileToCache(file);
            }
        }

        /*
          resync the file information if requested
         */
        if (getFileSystemManager().getCacheStrategy().equals(CacheStrategy.ON_RESOLVE)) {
            file.refresh();
        }
        return file;
    }

    /**
     * Finds a file in this file system.
     *
     * @param nameStr The name of the file to resolve.
     * @return The located FileObject or null if none could be located.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public FileObject resolveFile(final String nameStr) throws FileSystemException {
        // Resolve the name, and create the file
        return resolveFile(getFileSystemManager().resolveName(rootName, nameStr));
    }

    /**
     * Sets the attribute with the specified name. The default implementation simply throws an exception.
     *
     * @param attrName the attribute name.
     * @param value The object to associate with the attribute.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public void setAttribute(final String attrName, final Object value) throws FileSystemException {
        throw new FileSystemException("vfs.provider/set-attribute-not-supported.error");
    }

    void setCacheKey(final FileSystemKey cacheKey) {
        this.cacheKey = cacheKey;
    }

    void streamClosed() {
        if (openStreams.decrementAndGet() == 0) {
            notifyAllStreamsClosed();
        }
    }

    void streamOpened() {
        openStreams.incrementAndGet();
    }
}
