/*
 * 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.impl;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Objects;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.VfsLog;
import org.apache.commons.vfs2.operations.FileOperationProvider;
import org.apache.commons.vfs2.provider.FileProvider;
import org.apache.commons.vfs2.util.Messages;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

/**
 * A {@link org.apache.commons.vfs2.FileSystemManager} that configures itself from an XML (Default: providers.xml)
 * configuration file.
 * <p>
 * Certain providers are only loaded and available if the dependent library is in your classpath. You have to configure
 * your debugging facility to log "debug" messages to see if a provider was skipped due to "unresolved externals".
 * </p>
 */
public class StandardFileSystemManager extends DefaultFileSystemManager {
    private static final String CONFIG_RESOURCE = "providers.xml";
    private static final String PLUGIN_CONFIG_RESOURCE = "META-INF/vfs-providers.xml";

    private URL configUri;
    private ClassLoader classLoader;

    /**
     * Sets the configuration file for this manager.
     *
     * @param configUri The URI for this manager.
     */
    public void setConfiguration(final String configUri) {
        try {
            setConfiguration(new URL(configUri));
        } catch (final MalformedURLException e) {
            getLogger().warn(e.getLocalizedMessage(), e);
        }
    }

    /**
     * Sets the configuration file for this manager.
     *
     * @param configUri The URI forthis manager.
     */
    public void setConfiguration(final URL configUri) {
        this.configUri = configUri;
    }

    /**
     * Sets the ClassLoader to use to load the providers. Default is to use the ClassLoader that loaded this class.
     *
     * @param classLoader The ClassLoader.
     */
    public void setClassLoader(final ClassLoader classLoader) {
        this.classLoader = classLoader;
    }

    /**
     * Initializes this manager. Adds the providers and replicator.
     *
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public void init() throws FileSystemException {
        // Set the replicator and temporary file store (use the same component)
        final DefaultFileReplicator replicator = createDefaultFileReplicator();
        setReplicator(new PrivilegedFileReplicator(replicator));
        setTemporaryFileStore(replicator);

        if (configUri == null) {
            // Use default config
            final URL url = getClass().getResource(CONFIG_RESOURCE);
            FileSystemException.requireNonNull(url, "vfs.impl/find-config-file.error", CONFIG_RESOURCE);
            configUri = url;
        }

        configure(configUri);
        configurePlugins();

        // Initialise super-class
        super.init();
    }

    /**
     * Scans the classpath to find any droped plugin.
     * <p>
     * The plugin-description has to be in {@code /META-INF/vfs-providers.xml}.
     * </p>
     *
     * @throws FileSystemException if an error occurs.
     */
    protected void configurePlugins() throws FileSystemException {
        Enumeration<URL> enumResources;
        try {
            enumResources = loadResources(PLUGIN_CONFIG_RESOURCE);
        } catch (final IOException e) {
            throw new FileSystemException(e);
        }

        while (enumResources.hasMoreElements()) {
            final URL url = enumResources.nextElement();
            configure(url);
        }
    }

    /**
     * Returns a class loader or null since some Java implementation is null for the bootstrap class loader.
     *
     * @return A class loader or null since some Java implementation is null for the bootstrap class loader.
     */
    private ClassLoader findClassLoader() {
        if (classLoader != null) {
            return classLoader;
        }
        final ClassLoader cl = Thread.currentThread().getContextClassLoader();
        if (cl != null) {
            return cl;
        }
        return getValidClassLoader(getClass());
    }

    protected DefaultFileReplicator createDefaultFileReplicator() {
        return new DefaultFileReplicator();
    }

    /**
     * Configures this manager from an XML configuration file.
     *
     * @param configUri The URI of the configuration.
     * @throws FileSystemException if an error occus.
     */
    private void configure(final URL configUri) throws FileSystemException {
        InputStream configStream = null;
        try {
            // Load up the config
            // TODO - validate
            final DocumentBuilder builder = createDocumentBuilder();
            configStream = configUri.openStream();
            final Element config = builder.parse(configStream).getDocumentElement();

            configure(config);
        } catch (final Exception e) {
            throw new FileSystemException("vfs.impl/load-config.error", configUri.toString(), e);
        } finally {
            if (configStream != null) {
                try {
                    configStream.close();
                } catch (final IOException e) {
                    getLogger().warn(e.getLocalizedMessage(), e);
                }
            }
        }
    }

    /**
     * Configures this manager from an XML configuration file.
     *
     * @param configUri The URI of the configuration.
     * @param configStream An InputStream containing the configuration.
     * @throws FileSystemException if an error occurs.
     */
    @SuppressWarnings("unused")
    private void configure(final String configUri, final InputStream configStream) throws FileSystemException {
        try {
            // Load up the config
            // TODO - validate
            final DocumentBuilder builder = createDocumentBuilder();
            final Element config = builder.parse(configStream).getDocumentElement();

            configure(config);

        } catch (final Exception e) {
            throw new FileSystemException("vfs.impl/load-config.error", configUri, e);
        }
    }

    /**
     * Configure and create a DocumentBuilder
     *
     * @return A DocumentBuilder for the configuration.
     * @throws ParserConfigurationException if an error occurs.
     */
    private DocumentBuilder createDocumentBuilder() throws ParserConfigurationException {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setIgnoringElementContentWhitespace(true);
        factory.setIgnoringComments(true);
        factory.setExpandEntityReferences(true);
        return factory.newDocumentBuilder();
    }

    /**
     * Configures this manager from an parsed XML configuration file
     *
     * @param config The configuration Element.
     * @throws FileSystemException if an error occurs.
     */
    private void configure(final Element config) throws FileSystemException {
        // Add the providers
        final NodeList providers = config.getElementsByTagName("provider");
        final int count = providers.getLength();
        for (int i = 0; i < count; i++) {
            final Element provider = (Element) providers.item(i);
            addProvider(provider, false);
        }

        // Add the operation providers
        final NodeList operationProviders = config.getElementsByTagName("operationProvider");
        for (int i = 0; i < operationProviders.getLength(); i++) {
            final Element operationProvider = (Element) operationProviders.item(i);
            addOperationProvider(operationProvider);
        }

        // Add the default provider
        final NodeList defProviders = config.getElementsByTagName("default-provider");
        if (defProviders.getLength() > 0) {
            final Element provider = (Element) defProviders.item(0);
            addProvider(provider, true);
        }

        // Add the mime-type maps
        final NodeList mimeTypes = config.getElementsByTagName("mime-type-map");
        for (int i = 0; i < mimeTypes.getLength(); i++) {
            final Element map = (Element) mimeTypes.item(i);
            addMimeTypeMap(map);
        }

        // Add the extension maps
        final NodeList extensions = config.getElementsByTagName("extension-map");
        for (int i = 0; i < extensions.getLength(); i++) {
            final Element map = (Element) extensions.item(i);
            addExtensionMap(map);
        }
    }

    /**
     * Adds an extension map.
     *
     * @param map containing the Elements.
     */
    private void addExtensionMap(final Element map) {
        final String extension = map.getAttribute("extension");
        final String scheme = map.getAttribute("scheme");
        if (scheme != null && scheme.length() > 0) {
            addExtensionMap(extension, scheme);
        }
    }

    /**
     * Adds a mime-type map.
     *
     * @param map containing the Elements.
     */
    private void addMimeTypeMap(final Element map) {
        final String mimeType = map.getAttribute("mime-type");
        final String scheme = map.getAttribute("scheme");
        addMimeTypeMap(mimeType, scheme);
    }

    /**
     * Adds a provider from a provider definition.
     *
     * @param providerDef the provider definition
     * @param isDefault true if the default should be used.
     * @throws FileSystemException if an error occurs.
     */
    private void addProvider(final Element providerDef, final boolean isDefault) throws FileSystemException {
        final String classname = providerDef.getAttribute("class-name");

        // Make sure all required schemes are available
        final String[] requiredSchemes = getRequiredSchemes(providerDef);
        for (final String requiredScheme : requiredSchemes) {
            if (!hasProvider(requiredScheme)) {
                final String msg = Messages.getString("vfs.impl/skipping-provider-scheme.debug", classname,
                        requiredScheme);
                VfsLog.debug(getLogger(), getLogger(), msg);
                return;
            }
        }

        // Make sure all required classes are in classpath
        final String[] requiredClasses = getRequiredClasses(providerDef);
        for (final String requiredClass : requiredClasses) {
            if (!findClass(requiredClass)) {
                final String msg = Messages.getString("vfs.impl/skipping-provider.debug", classname, requiredClass);
                VfsLog.debug(getLogger(), getLogger(), msg);
                return;
            }
        }

        // Create and register the provider
        final FileProvider provider = (FileProvider) createInstance(classname);
        final String[] schemas = getSchemas(providerDef);
        if (schemas.length > 0) {
            addProvider(schemas, provider);
        }

        // Set as default, if required
        if (isDefault) {
            setDefaultProvider(provider);
        }
    }

    /**
     * Adds a operationProvider from a operationProvider definition.
     */
    private void addOperationProvider(final Element providerDef) throws FileSystemException {
        final String classname = providerDef.getAttribute("class-name");

        // Attach only to available schemas
        final String[] schemas = getSchemas(providerDef);
        for (final String schema : schemas) {
            if (hasProvider(schema)) {
                final FileOperationProvider operationProvider = (FileOperationProvider) createInstance(classname);
                addOperationProvider(schema, operationProvider);
            }
        }
    }

    /**
     * Tests if a class is available.
     */
    private boolean findClass(final String className) {
        try {
            loadClass(className);
            return true;
        } catch (final ClassNotFoundException e) {
            return false;
        }
    }

    /**
     * Extracts the required classes from a provider definition.
     */
    private String[] getRequiredClasses(final Element providerDef) {
        final ArrayList<String> classes = new ArrayList<>();
        final NodeList deps = providerDef.getElementsByTagName("if-available");
        final int count = deps.getLength();
        for (int i = 0; i < count; i++) {
            final Element dep = (Element) deps.item(i);
            final String className = dep.getAttribute("class-name");
            if (className != null && className.length() > 0) {
                classes.add(className);
            }
        }
        return classes.toArray(new String[classes.size()]);
    }

    /**
     * Extracts the required schemes from a provider definition.
     */
    private String[] getRequiredSchemes(final Element providerDef) {
        final ArrayList<String> schemes = new ArrayList<>();
        final NodeList deps = providerDef.getElementsByTagName("if-available");
        final int count = deps.getLength();
        for (int i = 0; i < count; i++) {
            final Element dep = (Element) deps.item(i);
            final String scheme = dep.getAttribute("scheme");
            if (scheme != null && scheme.length() > 0) {
                schemes.add(scheme);
            }
        }
        return schemes.toArray(new String[schemes.size()]);
    }

    /**
     * Extracts the schema names from a provider definition.
     */
    private String[] getSchemas(final Element provider) {
        final ArrayList<String> schemas = new ArrayList<>();
        final NodeList schemaElements = provider.getElementsByTagName("scheme");
        final int count = schemaElements.getLength();
        for (int i = 0; i < count; i++) {
            final Element scheme = (Element) schemaElements.item(i);
            schemas.add(scheme.getAttribute("name"));
        }
        return schemas.toArray(new String[schemas.size()]);
    }

    private ClassLoader getValidClassLoader(final Class<?> clazz) {
        return validateClassLoader(clazz.getClassLoader(), clazz);
    }

    private ClassLoader validateClassLoader(final ClassLoader clazzLoader, final Class<?> clazz) {
        return Objects.requireNonNull(clazzLoader, "The class loader for " + clazz
                + " is null; some Java implementions use null for the bootstrap class loader.");
    }

    /**
     * Creates a provider.
     */
    private Object createInstance(final String className) throws FileSystemException {
        try {
            final Class<?> clazz = loadClass(className);
            return clazz.newInstance();
        } catch (final Exception e) {
            throw new FileSystemException("vfs.impl/create-provider.error", className, e);
        }
    }

    /**
     * Load a class from different class loaders.
     *
     * @throws ClassNotFoundException if last {@code loadClass} failed.
     * @see #findClassLoader()
     */
    private Class<?> loadClass(final String className) throws ClassNotFoundException {
        try {
            return findClassLoader().loadClass(className);
        } catch (final ClassNotFoundException e) {
            return getValidClassLoader(getClass()).loadClass(className);
        }
    }

    /**
     * Resolve resources from different class loaders.
     *
     * @throws IOException if {@code getResource} failed.
     * @see #findClassLoader()
     */
    private Enumeration<URL> loadResources(final String name) throws IOException {
        Enumeration<URL> res = findClassLoader().getResources(name);
        if (res == null || !res.hasMoreElements()) {
            res = getValidClassLoader(getClass()).getResources(name);
        }
        return res;
    }

}
