/*
 * 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.configuration2.io;

import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.commons.configuration2.ex.ConfigurationException;
import org.apache.commons.configuration2.io.FileLocator.FileLocatorBuilder;
import org.apache.commons.configuration2.sync.LockMode;
import org.apache.commons.configuration2.sync.NoOpSynchronizer;
import org.apache.commons.configuration2.sync.Synchronizer;
import org.apache.commons.configuration2.sync.SynchronizerSupport;
import org.apache.commons.logging.LogFactory;

/**
 * <p>
 * A class that manages persistence of an associated {@link FileBased} object.
 * </p>
 * <p>
 * Instances of this class can be used to load and save arbitrary objects implementing the {@code FileBased} interface
 * in a convenient way from and to various locations. At construction time the {@code FileBased} object to manage is
 * passed in. Basically, this object is assigned a location from which it is loaded and to which it can be saved. The
 * following possibilities exist to specify such a location:
 * </p>
 * <ul>
 * <li>URLs: With the method {@code setURL()} a full URL to the configuration source can be specified. This is the most
 * flexible way. Note that the {@code save()} methods support only <em>file:</em> URLs.</li>
 * <li>Files: The {@code setFile()} method allows to specify the configuration source as a file. This can be either a
 * relative or an absolute file. In the former case the file is resolved based on the current directory.</li>
 * <li>As file paths in string form: With the {@code setPath()} method a full path to a configuration file can be
 * provided as a string.</li>
 * <li>Separated as base path and file name: The base path is a string defining either a local directory or a URL. It
 * can be set using the {@code setBasePath()} method. The file name, non surprisingly, defines the name of the
 * configuration file.</li>
 * </ul>
 * <p>
 * An instance stores a location. The {@code load()} and {@code save()} methods that do not take an argument make use of
 * this internal location. Alternatively, it is also possible to use overloaded variants of {@code load()} and
 * {@code save()} which expect a location. In these cases the location specified takes precedence over the internal one;
 * the internal location is not changed.
 * </p>
 * <p>
 * The actual position of the file to be loaded is determined by a {@link FileLocationStrategy} based on the location
 * information that has been provided. By providing a custom location strategy the algorithm for searching files can be
 * adapted. Save operations require more explicit information. They cannot rely on a location strategy because the file
 * to be written may not yet exist. So there may be some differences in the way location information is interpreted by
 * load and save operations. In order to avoid this, the following approach is recommended:
 * </p>
 * <ul>
 * <li>Use the desired {@code setXXX()} methods to define the location of the file to be loaded.</li>
 * <li>Call the {@code locate()} method. This method resolves the referenced file (if possible) and fills out all
 * supported location information.</li>
 * <li>Later on, {@code save()} can be called. This method now has sufficient information to store the file at the
 * correct location.</li>
 * </ul>
 * <p>
 * When loading or saving a {@code FileBased} object some additional functionality is performed if the object implements
 * one of the following interfaces:
 * </p>
 * <ul>
 * <li>{@code FileLocatorAware}: In this case an object with the current file location is injected before the load or
 * save operation is executed. This is useful for {@code FileBased} objects that depend on their current location, e.g.
 * to resolve relative path names.</li>
 * <li>{@code SynchronizerSupport}: If this interface is implemented, load and save operations obtain a write lock on
 * the {@code FileBased} object before they access it. (In case of a save operation, a read lock would probably be
 * sufficient, but because of the possible injection of a {@link FileLocator} object it is not allowed to perform
 * multiple save operations in parallel; therefore, by obtaining a write lock, we are on the safe side.)</li>
 * </ul>
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @since 2.0
 */
public class FileHandler {
    /**
     * An internal class that performs all update operations of the handler's {@code FileLocator} in a safe way even if
     * there is concurrent access. This class implements anon-blocking algorithm for replacing the immutable
     * {@code FileLocator} instance stored in an atomic reference by a manipulated instance. (If we already had lambdas,
     * this could be done without a class in a more elegant way.)
     */
    private abstract class AbstractUpdater {
        /**
         * Performs an update of the enclosing file handler's {@code FileLocator} object.
         */
        public void update() {
            boolean done;
            do {
                final FileLocator oldLocator = fileLocator.get();
                final FileLocatorBuilder builder = FileLocatorUtils.fileLocator(oldLocator);
                updateBuilder(builder);
                done = fileLocator.compareAndSet(oldLocator, builder.create());
            } while (!done);
            fireLocationChangedEvent();
        }

        /**
         * Updates the passed in builder object to apply the manipulation to be performed by this {@code Updater}. The builder
         * has been setup with the former content of the {@code FileLocator} to be manipulated.
         *
         * @param builder the builder for creating an updated {@code FileLocator}
         */
        protected abstract void updateBuilder(FileLocatorBuilder builder);
    }

    /** Constant for the URI scheme for files. */
    private static final String FILE_SCHEME = "file:";

    /** Constant for the URI scheme for files with slashes. */
    private static final String FILE_SCHEME_SLASH = FILE_SCHEME + "//";

    /**
     * A dummy implementation of {@code SynchronizerSupport}. This object is used when the file handler's content does not
     * implement the {@code SynchronizerSupport} interface. All methods are just empty dummy implementations.
     */
    private static final SynchronizerSupport DUMMY_SYNC_SUPPORT = new SynchronizerSupport() {
        @Override
        public Synchronizer getSynchronizer() {
            return NoOpSynchronizer.INSTANCE;
        }

        @Override
        public void lock(final LockMode mode) {
        }

        @Override
        public void setSynchronizer(final Synchronizer sync) {
        }

        @Override
        public void unlock(final LockMode mode) {
        }
    };

    /** The file-based object managed by this handler. */
    private final FileBased content;

    /** A reference to the current {@code FileLocator} object. */
    private final AtomicReference<FileLocator> fileLocator;

    /** A collection with the registered listeners. */
    private final List<FileHandlerListener> listeners = new CopyOnWriteArrayList<>();

    /**
     * Creates a new instance of {@code FileHandler} which is not associated with a {@code FileBased} object and thus does
     * not have a content. Objects of this kind can be used to define a file location, but it is not possible to actually
     * load or save data.
     */
    public FileHandler() {
        this(null);
    }

    /**
     * Creates a new instance of {@code FileHandler} and sets the managed {@code FileBased} object.
     *
     * @param obj the file-based object to manage
     */
    public FileHandler(final FileBased obj) {
        this(obj, emptyFileLocator());
    }

    /**
     * Creates a new instance of {@code FileHandler} which is associated with the given {@code FileBased} object and the
     * location defined for the given {@code FileHandler} object. A copy of the location of the given {@code FileHandler} is
     * created. This constructor is a possibility to associate a file location with a {@code FileBased} object.
     *
     * @param obj the {@code FileBased} object to manage
     * @param c the {@code FileHandler} from which to copy the location (must not be <b>null</b>)
     * @throws IllegalArgumentException if the {@code FileHandler} is <b>null</b>
     */
    public FileHandler(final FileBased obj, final FileHandler c) {
        this(obj, checkSourceHandler(c).getFileLocator());
    }

    /**
     * Creates a new instance of {@code FileHandler} based on the given {@code FileBased} and {@code FileLocator} objects.
     *
     * @param obj the {@code FileBased} object to manage
     * @param locator the {@code FileLocator}
     */
    private FileHandler(final FileBased obj, final FileLocator locator) {
        content = obj;
        fileLocator = new AtomicReference<>(locator);
    }

    /**
     * Helper method for checking a file handler which is to be copied. Throws an exception if the handler is <b>null</b>.
     *
     * @param c the {@code FileHandler} from which to copy the location
     * @return the same {@code FileHandler}
     */
    private static FileHandler checkSourceHandler(final FileHandler c) {
        if (c == null) {
            throw new IllegalArgumentException("FileHandler to assign must not be null!");
        }
        return c;
    }

    /**
     * A helper method for closing a stream. Occurring exceptions will be ignored.
     *
     * @param cl the stream to be closed (may be <b>null</b>)
     */
    private static void closeSilent(final Closeable cl) {
        try {
            if (cl != null) {
                cl.close();
            }
        } catch (final IOException e) {
            LogFactory.getLog(FileHandler.class).warn("Exception when closing " + cl, e);
        }
    }

    /**
     * Creates a {@code File} object from the content of the given {@code FileLocator} object. If the locator is not
     * defined, result is <b>null</b>.
     *
     * @param loc the {@code FileLocator}
     * @return a {@code File} object pointing to the associated file
     */
    private static File createFile(final FileLocator loc) {
        if (loc.getFileName() == null && loc.getSourceURL() == null) {
            return null;
        }
        if (loc.getSourceURL() != null) {
            return FileLocatorUtils.fileFromURL(loc.getSourceURL());
        }
        return FileLocatorUtils.getFile(loc.getBasePath(), loc.getFileName());
    }

    /**
     * Creates an uninitialized file locator.
     *
     * @return the locator
     */
    private static FileLocator emptyFileLocator() {
        return FileLocatorUtils.fileLocator().create();
    }

    /**
     * Creates a new {@code FileHandler} instance from properties stored in a map. This method tries to extract a
     * {@link FileLocator} from the map. A new {@code FileHandler} is created based on this {@code FileLocator}.
     *
     * @param map the map (may be <b>null</b>)
     * @return the newly created {@code FileHandler}
     * @see FileLocatorUtils#fromMap(Map)
     */
    public static FileHandler fromMap(final Map<String, ?> map) {
        return new FileHandler(null, FileLocatorUtils.fromMap(map));
    }

    /**
     * Normalizes URLs to files. Ensures that file URLs start with the correct protocol.
     *
     * @param fileName the string to be normalized
     * @return the normalized file URL
     */
    private static String normalizeFileURL(String fileName) {
        if (fileName != null && fileName.startsWith(FILE_SCHEME) && !fileName.startsWith(FILE_SCHEME_SLASH)) {
            fileName = FILE_SCHEME_SLASH + fileName.substring(FILE_SCHEME.length());
        }
        return fileName;
    }

    /**
     * Adds a listener to this {@code FileHandler}. It is notified about property changes and IO operations.
     *
     * @param l the listener to be added (must not be <b>null</b>)
     * @throws IllegalArgumentException if the listener is <b>null</b>
     */
    public void addFileHandlerListener(final FileHandlerListener l) {
        if (l == null) {
            throw new IllegalArgumentException("Listener must not be null!");
        }
        listeners.add(l);
    }

    /**
     * Checks whether a content object is available. If not, an exception is thrown. This method is called whenever the
     * content object is accessed.
     *
     * @throws ConfigurationException if not content object is defined
     */
    private void checkContent() throws ConfigurationException {
        if (getContent() == null) {
            throw new ConfigurationException("No content available!");
        }
    }

    /**
     * Checks whether a content object is available and returns the current {@code FileLocator}. If there is no content
     * object, an exception is thrown. This is a typical operation to be performed before a load() or save() operation.
     *
     * @return the current {@code FileLocator} to be used for the calling operation
     * @throws ConfigurationException if not content object is defined
     */
    private FileLocator checkContentAndGetLocator() throws ConfigurationException {
        checkContent();
        return getFileLocator();
    }

    /**
     * Clears the location of this {@code FileHandler}. Afterwards this handler does not point to any valid file.
     */
    public void clearLocation() {
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.basePath(null).fileName(null).sourceURL(null);
            }
        }.update();
    }

    /**
     * Creates a {@code FileLocator} which is a copy of the passed in one, but has the given file name set to reference the
     * target file.
     *
     * @param fileName the file name
     * @param locator the {@code FileLocator} to copy
     * @return the manipulated {@code FileLocator} with the file name
     */
    private FileLocator createLocatorWithFileName(final String fileName, final FileLocator locator) {
        return FileLocatorUtils.fileLocator(locator).sourceURL(null).fileName(fileName).create();
    }

    /**
     * Obtains a {@code SynchronizerSupport} for the current content. If the content implements this interface, it is
     * returned. Otherwise, result is a dummy object. This method is called before load and save operations. The returned
     * object is used for synchronization.
     *
     * @return the {@code SynchronizerSupport} for synchronization
     */
    private SynchronizerSupport fetchSynchronizerSupport() {
        if (getContent() instanceof SynchronizerSupport) {
            return (SynchronizerSupport) getContent();
        }
        return DUMMY_SYNC_SUPPORT;
    }

    /**
     * Notifies the registered listeners about a completed load operation.
     */
    private void fireLoadedEvent() {
        listeners.forEach(l -> l.loaded(this));
    }

    /**
     * Notifies the registered listeners about the start of a load operation.
     */
    private void fireLoadingEvent() {
        listeners.forEach(l -> l.loading(this));
    }

    /**
     * Notifies the registered listeners about a property update.
     */
    private void fireLocationChangedEvent() {
        listeners.forEach(l -> l.locationChanged(this));
    }

    /**
     * Notifies the registered listeners about a completed save operation.
     */
    private void fireSavedEvent() {
        listeners.forEach(l -> l.saved(this));
    }

    /**
     * Notifies the registered listeners about the start of a save operation.
     */
    private void fireSavingEvent() {
        listeners.forEach(l -> l.saving(this));
    }

    /**
     * Gets the base path. If no base path is defined, but a URL, the base path is derived from there.
     *
     * @return the base path
     */
    public String getBasePath() {
        final FileLocator locator = getFileLocator();
        if (locator.getBasePath() != null) {
            return locator.getBasePath();
        }

        if (locator.getSourceURL() != null) {
            return FileLocatorUtils.getBasePath(locator.getSourceURL());
        }

        return null;
    }

    /**
     * Gets the {@code FileBased} object associated with this {@code FileHandler}.
     *
     * @return the associated {@code FileBased} object
     */
    public final FileBased getContent() {
        return content;
    }

    /**
     * Gets the encoding of the associated file. Result can be <b>null</b> if no encoding has been set.
     *
     * @return the encoding of the associated file
     */
    public String getEncoding() {
        return getFileLocator().getEncoding();
    }

    /**
     * Gets the location of the associated file as a {@code File} object. If the base path is a URL with a protocol
     * different than &quot;file&quot;, or the file is within a compressed archive, the return value will not point to a
     * valid file object.
     *
     * @return the location as {@code File} object; this can be <b>null</b>
     */
    public File getFile() {
        return createFile(getFileLocator());
    }

    /**
     * Gets a {@code FileLocator} object with the specification of the file stored by this {@code FileHandler}. Note that
     * this method returns the internal data managed by this {@code FileHandler} as it was defined. This is not necessarily
     * the same as the data returned by the single access methods like {@code getFileName()} or {@code getURL()}: These
     * methods try to derive missing data from other values that have been set.
     *
     * @return a {@code FileLocator} with the referenced file
     */
    public FileLocator getFileLocator() {
        return fileLocator.get();
    }

    /**
     * Gets the name of the file. If only a URL is defined, the file name is derived from there.
     *
     * @return the file name
     */
    public String getFileName() {
        final FileLocator locator = getFileLocator();
        if (locator.getFileName() != null) {
            return locator.getFileName();
        }

        if (locator.getSourceURL() != null) {
            return FileLocatorUtils.getFileName(locator.getSourceURL());
        }

        return null;
    }

    /**
     * Gets the {@code FileSystem} to be used by this object when locating files. Result is never <b>null</b>; if no file
     * system has been set, the default file system is returned.
     *
     * @return the used {@code FileSystem}
     */
    public FileSystem getFileSystem() {
        return FileLocatorUtils.getFileSystem(getFileLocator());
    }

    /**
     * Gets the {@code FileLocationStrategy} to be applied when accessing the associated file. This method never returns
     * <b>null</b>. If a {@code FileLocationStrategy} has been set, it is returned. Otherwise, result is the default
     * {@code FileLocationStrategy}.
     *
     * @return the {@code FileLocationStrategy} to be used
     */
    public FileLocationStrategy getLocationStrategy() {
        return FileLocatorUtils.getLocationStrategy(getFileLocator());
    }

    /**
     * Gets the full path to the associated file. The return value is a valid {@code File} path only if this location is
     * based on a file on the local disk. If the file was loaded from a packed archive, the returned value is the string
     * form of the URL from which the file was loaded.
     *
     * @return the full path to the associated file
     */
    public String getPath() {
        final FileLocator locator = getFileLocator();
        final File file = createFile(locator);
        return FileLocatorUtils.getFileSystem(locator).getPath(file, locator.getSourceURL(), locator.getBasePath(), locator.getFileName());
    }

    /**
     * Gets the location of the associated file as a URL. If a URL is set, it is directly returned. Otherwise, an attempt
     * to locate the referenced file is made.
     *
     * @return a URL to the associated file; can be <b>null</b> if the location is unspecified
     */
    public URL getURL() {
        final FileLocator locator = getFileLocator();
        return locator.getSourceURL() != null ? locator.getSourceURL() : FileLocatorUtils.locate(locator);
    }

    /**
     * Injects a {@code FileLocator} pointing to the specified URL if the current {@code FileBased} object implements the
     * {@code FileLocatorAware} interface.
     *
     * @param url the URL for the locator
     */
    private void injectFileLocator(final URL url) {
        if (url == null) {
            injectNullFileLocator();
        } else if (getContent() instanceof FileLocatorAware) {
            final FileLocator locator = prepareNullLocatorBuilder().sourceURL(url).create();
            ((FileLocatorAware) getContent()).initFileLocator(locator);
        }
    }

    /**
     * Checks whether the associated {@code FileBased} object implements the {@code FileLocatorAware} interface. If this is
     * the case, a {@code FileLocator} instance is injected which returns only <b>null</b> values. This method is called if
     * no file location is available (e.g. if data is to be loaded from a stream). The encoding of the injected locator is
     * derived from this object.
     */
    private void injectNullFileLocator() {
        if (getContent() instanceof FileLocatorAware) {
            final FileLocator locator = prepareNullLocatorBuilder().create();
            ((FileLocatorAware) getContent()).initFileLocator(locator);
        }
    }

    /**
     * Tests whether a location is defined for this {@code FileHandler}.
     *
     * @return <b>true</b> if a location is defined, <b>false</b> otherwise
     */
    public boolean isLocationDefined() {
        return FileLocatorUtils.isLocationDefined(getFileLocator());
    }

    /**
     * Loads the associated file from the underlying location. If no location has been set, an exception is thrown.
     *
     * @throws ConfigurationException if loading of the configuration fails
     */
    public void load() throws ConfigurationException {
        load(checkContentAndGetLocator());
    }

    /**
     * Loads the associated file from the specified {@code File}.
     *
     * @param file the file to load
     * @throws ConfigurationException if an error occurs
     */
    public void load(final File file) throws ConfigurationException {
        final URL url;
        try {
            url = FileLocatorUtils.toURL(file);
        } catch (final MalformedURLException e1) {
            throw new ConfigurationException("Cannot create URL from file " + file);
        }

        load(url);
    }

    /**
     * Internal helper method for loading the associated file from the location specified in the given {@code FileLocator}.
     *
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs
     */
    private void load(final FileLocator locator) throws ConfigurationException {
        load(FileLocatorUtils.locateOrThrow(locator), locator);
    }

    /**
     * Loads the associated file from the specified stream, using the encoding returned by {@link #getEncoding()}.
     *
     * @param in the input stream
     * @throws ConfigurationException if an error occurs during the load operation
     */
    public void load(final InputStream in) throws ConfigurationException {
        load(in, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for loading a file from the given input stream.
     *
     * @param in the input stream
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs
     */
    private void load(final InputStream in, final FileLocator locator) throws ConfigurationException {
        load(in, locator.getEncoding());
    }

    /**
     * Loads the associated file from the specified stream, using the specified encoding. If the encoding is <b>null</b>,
     * the default encoding is used.
     *
     * @param in the input stream
     * @param encoding the encoding used, {@code null} to use the default encoding
     * @throws ConfigurationException if an error occurs during the load operation
     */
    public void load(final InputStream in, final String encoding) throws ConfigurationException {
        loadFromStream(in, encoding, null);
    }

    /**
     * Loads the associated file from the specified reader.
     *
     * @param in the reader
     * @throws ConfigurationException if an error occurs during the load operation
     */
    public void load(final Reader in) throws ConfigurationException {
        checkContent();
        injectNullFileLocator();
        loadFromReader(in);
    }

    /**
     * Loads the associated file from the given file name. The file name is interpreted in the context of the already set
     * location (e.g. if it is a relative file name, a base path is applied if available). The underlying location is not
     * changed.
     *
     * @param fileName the name of the file to be loaded
     * @throws ConfigurationException if an error occurs
     */
    public void load(final String fileName) throws ConfigurationException {
        load(fileName, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for loading a file from a file name.
     *
     * @param fileName the file name
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs
     */
    private void load(final String fileName, final FileLocator locator) throws ConfigurationException {
        final FileLocator locFileName = createLocatorWithFileName(fileName, locator);
        final URL url = FileLocatorUtils.locateOrThrow(locFileName);
        load(url, locator);
    }

    /**
     * Loads the associated file from the specified URL. The location stored in this object is not changed.
     *
     * @param url the URL of the file to be loaded
     * @throws ConfigurationException if an error occurs
     */
    public void load(final URL url) throws ConfigurationException {
        load(url, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for loading a file from the given URL.
     *
     * @param url the URL
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs
     */
    private void load(final URL url, final FileLocator locator) throws ConfigurationException {
        InputStream in = null;

        try {
            final FileSystem fileSystem = FileLocatorUtils.getFileSystem(locator);
            final URLConnectionOptions urlConnectionOptions = locator.getURLConnectionOptions();
            in = urlConnectionOptions == null ? fileSystem.getInputStream(url) : fileSystem.getInputStream(url, urlConnectionOptions);
            loadFromStream(in, locator.getEncoding(), url);
        } catch (final ConfigurationException e) {
            throw e;
        } catch (final Exception e) {
            throw new ConfigurationException("Unable to load the configuration from the URL " + url, e);
        } finally {
            closeSilent(in);
        }
    }

    /**
     * Internal helper method for loading a file from the given reader.
     *
     * @param in the reader
     * @throws ConfigurationException if an error occurs
     */
    private void loadFromReader(final Reader in) throws ConfigurationException {
        fireLoadingEvent();
        try {
            getContent().read(in);
        } catch (final IOException ioex) {
            throw new ConfigurationException(ioex);
        } finally {
            fireLoadedEvent();
        }
    }

    /**
     * Internal helper method for loading a file from an input stream.
     *
     * @param in the input stream
     * @param encoding the encoding
     * @param url the URL of the file to be loaded (if known)
     * @throws ConfigurationException if an error occurs
     */
    private void loadFromStream(final InputStream in, final String encoding, final URL url) throws ConfigurationException {
        checkContent();
        final SynchronizerSupport syncSupport = fetchSynchronizerSupport();
        syncSupport.lock(LockMode.WRITE);
        try {
            injectFileLocator(url);

            if (getContent() instanceof InputStreamSupport) {
                loadFromStreamDirectly(in);
            } else {
                loadFromTransformedStream(in, encoding);
            }
        } finally {
            syncSupport.unlock(LockMode.WRITE);
        }
    }

    /**
     * Loads data from an input stream if the associated {@code FileBased} object implements the {@code InputStreamSupport}
     * interface.
     *
     * @param in the input stream
     * @throws ConfigurationException if an error occurs
     */
    private void loadFromStreamDirectly(final InputStream in) throws ConfigurationException {
        try {
            ((InputStreamSupport) getContent()).read(in);
        } catch (final IOException e) {
            throw new ConfigurationException(e);
        }
    }

    /**
     * Internal helper method for transforming an input stream to a reader and reading its content.
     *
     * @param in the input stream
     * @param encoding the encoding
     * @throws ConfigurationException if an error occurs
     */
    private void loadFromTransformedStream(final InputStream in, final String encoding) throws ConfigurationException {
        Reader reader = null;

        if (encoding != null) {
            try {
                reader = new InputStreamReader(in, encoding);
            } catch (final UnsupportedEncodingException e) {
                throw new ConfigurationException("The requested encoding is not supported, try the default encoding.", e);
            }
        }

        if (reader == null) {
            reader = new InputStreamReader(in);
        }

        loadFromReader(reader);
    }

    /**
     * Locates the referenced file if necessary and ensures that the associated {@link FileLocator} is fully initialized.
     * When accessing the referenced file the information stored in the associated {@code FileLocator} is used. If this
     * information is incomplete (e.g. only the file name is set), an attempt to locate the file may have to be performed on
     * each access. By calling this method such an attempt is performed once, and the results of a successful localization
     * are stored. Hence, later access to the referenced file can be more efficient. Also, all properties pointing to the
     * referenced file in this object's {@code FileLocator} are set (i.e. the URL, the base path, and the file name). If the
     * referenced file cannot be located, result is <b>false</b>. This means that the information in the current
     * {@code FileLocator} is insufficient or wrong. If the {@code FileLocator} is already fully defined, it is not changed.
     *
     * @return a flag whether the referenced file could be located successfully
     * @see FileLocatorUtils#fullyInitializedLocator(FileLocator)
     */
    public boolean locate() {
        boolean result;
        boolean done;

        do {
            final FileLocator locator = getFileLocator();
            FileLocator fullLocator = FileLocatorUtils.fullyInitializedLocator(locator);
            if (fullLocator == null) {
                result = false;
                fullLocator = locator;
            } else {
                result = fullLocator != locator || FileLocatorUtils.isFullyInitialized(locator);
            }
            done = fileLocator.compareAndSet(locator, fullLocator);
        } while (!done);

        return result;
    }

    /**
     * Prepares a builder for a {@code FileLocator} which does not have a defined file location. Other properties (e.g.
     * encoding or file system) are initialized from the {@code FileLocator} associated with this object.
     *
     * @return the initialized builder for a {@code FileLocator}
     */
    private FileLocatorBuilder prepareNullLocatorBuilder() {
        return FileLocatorUtils.fileLocator(getFileLocator()).sourceURL(null).basePath(null).fileName(null);
    }

    /**
     * Removes the specified listener from this object.
     *
     * @param l the listener to be removed
     */
    public void removeFileHandlerListener(final FileHandlerListener l) {
        listeners.remove(l);
    }

    /**
     * Resets the {@code FileSystem} used by this object. It is set to the default file system.
     */
    public void resetFileSystem() {
        setFileSystem(null);
    }

    /**
     * Saves the associated file to the current location set for this object. Before this method can be called a valid
     * location must have been set.
     *
     * @throws ConfigurationException if an error occurs or no location has been set yet
     */
    public void save() throws ConfigurationException {
        save(checkContentAndGetLocator());
    }

    /**
     * Saves the associated file to the specified {@code File}. The file is created automatically if it doesn't exist. This
     * does not change the location of this object (use {@link #setFile} if you need it).
     *
     * @param file the target file
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final File file) throws ConfigurationException {
        save(file, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for saving data to the given {@code File}.
     *
     * @param file the target file
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    private void save(final File file, final FileLocator locator) throws ConfigurationException {
        OutputStream out = null;

        try {
            out = FileLocatorUtils.getFileSystem(locator).getOutputStream(file);
            saveToStream(out, locator.getEncoding(), file.toURI().toURL());
        } catch (final MalformedURLException muex) {
            throw new ConfigurationException(muex);
        } finally {
            closeSilent(out);
        }
    }

    /**
     * Internal helper method for saving data to the internal location stored for this object.
     *
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    private void save(final FileLocator locator) throws ConfigurationException {
        if (!FileLocatorUtils.isLocationDefined(locator)) {
            throw new ConfigurationException("No file location has been set!");
        }

        if (locator.getSourceURL() != null) {
            save(locator.getSourceURL(), locator);
        } else {
            save(locator.getFileName(), locator);
        }
    }

    /**
     * Saves the associated file to the specified stream using the encoding returned by {@link #getEncoding()}.
     *
     * @param out the output stream
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final OutputStream out) throws ConfigurationException {
        save(out, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for saving a file to the given output stream.
     *
     * @param out the output stream
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    private void save(final OutputStream out, final FileLocator locator) throws ConfigurationException {
        save(out, locator.getEncoding());
    }

    /**
     * Saves the associated file to the specified stream using the specified encoding. If the encoding is <b>null</b>, the
     * default encoding is used.
     *
     * @param out the output stream
     * @param encoding the encoding to be used, {@code null} to use the default encoding
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final OutputStream out, final String encoding) throws ConfigurationException {
        saveToStream(out, encoding, null);
    }

    /**
     * Saves the associated file to the specified file name. This does not change the location of this object (use
     * {@link #setFileName(String)} if you need it).
     *
     * @param fileName the file name
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final String fileName) throws ConfigurationException {
        save(fileName, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for saving data to the given file name.
     *
     * @param fileName the path to the target file
     * @param locator the current {@code FileLocator}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    private void save(final String fileName, final FileLocator locator) throws ConfigurationException {
        final URL url;
        try {
            url = FileLocatorUtils.getFileSystem(locator).getURL(locator.getBasePath(), fileName);
        } catch (final MalformedURLException e) {
            throw new ConfigurationException(e);
        }

        if (url == null) {
            throw new ConfigurationException("Cannot locate configuration source " + fileName);
        }
        save(url, locator);
    }

    /**
     * Saves the associated file to the specified URL. This does not change the location of this object (use
     * {@link #setURL(URL)} if you need it).
     *
     * @param url the URL
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final URL url) throws ConfigurationException {
        save(url, checkContentAndGetLocator());
    }

    /**
     * Internal helper method for saving data to the given URL.
     *
     * @param url the target URL
     * @param locator the {@code FileLocator}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    private void save(final URL url, final FileLocator locator) throws ConfigurationException {
        OutputStream out = null;
        try {
            out = FileLocatorUtils.getFileSystem(locator).getOutputStream(url);
            saveToStream(out, locator.getEncoding(), url);
            if (out instanceof VerifiableOutputStream) {
                try {
                    ((VerifiableOutputStream) out).verify();
                } catch (final IOException e) {
                    throw new ConfigurationException(e);
                }
            }
        } finally {
            closeSilent(out);
        }
    }

    /**
     * Saves the associated file to the given {@code Writer}.
     *
     * @param out the {@code Writer}
     * @throws ConfigurationException if an error occurs during the save operation
     */
    public void save(final Writer out) throws ConfigurationException {
        checkContent();
        injectNullFileLocator();
        saveToWriter(out);
    }

    /**
     * Internal helper method for saving a file to the given stream.
     *
     * @param out the output stream
     * @param encoding the encoding
     * @param url the URL of the output file if known
     * @throws ConfigurationException if an error occurs
     */
    private void saveToStream(final OutputStream out, final String encoding, final URL url) throws ConfigurationException {
        checkContent();
        final SynchronizerSupport syncSupport = fetchSynchronizerSupport();
        syncSupport.lock(LockMode.WRITE);
        try {
            injectFileLocator(url);
            Writer writer = null;

            if (encoding != null) {
                try {
                    writer = new OutputStreamWriter(out, encoding);
                } catch (final UnsupportedEncodingException e) {
                    throw new ConfigurationException("The requested encoding is not supported, try the default encoding.", e);
                }
            }

            if (writer == null) {
                writer = new OutputStreamWriter(out);
            }

            saveToWriter(writer);
        } finally {
            syncSupport.unlock(LockMode.WRITE);
        }
    }

    /**
     * Internal helper method for saving a file into the given writer.
     *
     * @param out the writer
     * @throws ConfigurationException if an error occurs
     */
    private void saveToWriter(final Writer out) throws ConfigurationException {
        fireSavingEvent();
        try {
            getContent().write(out);
        } catch (final IOException ioex) {
            throw new ConfigurationException(ioex);
        } finally {
            fireSavedEvent();
        }
    }

    /**
     * Sets the base path. The base path is typically either a path to a directory or a URL. Together with the value passed
     * to the {@code setFileName()} method it defines the location of the configuration file to be loaded. The strategies
     * for locating the file are quite tolerant. For instance if the file name is already an absolute path or a fully
     * defined URL, the base path will be ignored. The base path can also be a URL, in which case the file name is
     * interpreted in this URL's context. If other methods are used for determining the location of the associated file
     * (e.g. {@code setFile()} or {@code setURL()}), the base path is automatically set. Setting the base path using this
     * method automatically sets the URL to <b>null</b> because it has to be determined anew based on the file name and the
     * base path.
     *
     * @param basePath the base path.
     */
    public void setBasePath(final String basePath) {
        final String path = normalizeFileURL(basePath);
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.basePath(path);
                builder.sourceURL(null);
            }
        }.update();
    }

    /**
     * Sets the encoding of the associated file. The encoding applies if binary files are loaded. Note that in this case
     * setting an encoding is recommended; otherwise the platform's default encoding is used.
     *
     * @param encoding the encoding of the associated file
     */
    public void setEncoding(final String encoding) {
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.encoding(encoding);
            }
        }.update();
    }

    /**
     * Sets the location of the associated file as a {@code File} object. The passed in {@code File} is made absolute if it
     * is not yet. Then the file's path component becomes the base path and its name component becomes the file name.
     *
     * @param file the location of the associated file
     */
    public void setFile(final File file) {
        final String fileName = file.getName();
        final String basePath = file.getParentFile() != null ? file.getParentFile().getAbsolutePath() : null;
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.fileName(fileName).basePath(basePath).sourceURL(null);
            }
        }.update();
    }

    /**
     * Sets the file to be accessed by this {@code FileHandler} as a {@code FileLocator} object.
     *
     * @param locator the {@code FileLocator} with the definition of the file to be accessed (must not be <b>null</b>
     * @throws IllegalArgumentException if the {@code FileLocator} is <b>null</b>
     */
    public void setFileLocator(final FileLocator locator) {
        if (locator == null) {
            throw new IllegalArgumentException("FileLocator must not be null!");
        }

        fileLocator.set(locator);
        fireLocationChangedEvent();
    }

    /**
     * Sets the name of the file. The passed in file name can contain a relative path. It must be used when referring files
     * with relative paths from classpath. Use {@code setPath()} to set a full qualified file name. The URL is set to
     * <b>null</b> as it has to be determined anew based on the file name and the base path.
     *
     * @param fileName the name of the file
     */
    public void setFileName(final String fileName) {
        final String name = normalizeFileURL(fileName);
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.fileName(name);
                builder.sourceURL(null);
            }
        }.update();
    }

    /**
     * Sets the {@code FileSystem} to be used by this object when locating files. If a <b>null</b> value is passed in, the
     * file system is reset to the default file system.
     *
     * @param fileSystem the {@code FileSystem}
     */
    public void setFileSystem(final FileSystem fileSystem) {
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.fileSystem(fileSystem);
            }
        }.update();
    }

    /**
     * Sets the {@code FileLocationStrategy} to be applied when accessing the associated file. The strategy is stored in the
     * underlying {@link FileLocator}. The argument can be <b>null</b>; this causes the default {@code FileLocationStrategy}
     * to be used.
     *
     * @param strategy the {@code FileLocationStrategy}
     * @see FileLocatorUtils#DEFAULT_LOCATION_STRATEGY
     */
    public void setLocationStrategy(final FileLocationStrategy strategy) {
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.locationStrategy(strategy);
            }

        }.update();
    }

    /**
     * Sets the location of the associated file as a full or relative path name. The passed in path should represent a valid
     * file name on the file system. It must not be used to specify relative paths for files that exist in classpath, either
     * plain file system or compressed archive, because this method expands any relative path to an absolute one which may
     * end in an invalid absolute path for classpath references.
     *
     * @param path the full path name of the associated file
     */
    public void setPath(final String path) {
        setFile(new File(path));
    }

    /**
     * Sets the location of the associated file as a URL. For loading this can be an arbitrary URL with a supported
     * protocol. If the file is to be saved, too, a URL with the &quot;file&quot; protocol should be provided. This method
     * sets the file name and the base path to <b>null</b>. They have to be determined anew based on the new URL.
     *
     * @param url the location of the file as URL
     */
    public void setURL(final URL url) {
        setURL(url, URLConnectionOptions.DEFAULT);
    }

    /**
     * Sets the location of the associated file as a URL. For loading this can be an arbitrary URL with a supported
     * protocol. If the file is to be saved, too, a URL with the &quot;file&quot; protocol should be provided. This method
     * sets the file name and the base path to <b>null</b>. They have to be determined anew based on the new URL.
     *
     * @param url the location of the file as URL
     * @param urlConnectionOptions URL connection options
     * @since 2.8.0
     */
    public void setURL(final URL url, final URLConnectionOptions urlConnectionOptions) {
        new AbstractUpdater() {
            @Override
            protected void updateBuilder(final FileLocatorBuilder builder) {
                builder.sourceURL(url);
                builder.urlConnectionOptions(urlConnectionOptions);
                builder.basePath(null).fileName(null);
            }
        }.update();
    }
}