/*
 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.activation;

import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * The CommandInfo class is used by CommandMap implementations to
 * describe the results of command requests. It provides the requestor
 * with both the verb requested, as well as an instance of the
 * bean. There is also a method that will return the name of the
 * class that implements the command but <i>it is not guaranteed to
 * return a valid value</i>. The reason for this is to allow CommandMap
 * implmentations that subclass CommandInfo to provide special
 * behavior. For example a CommandMap could dynamically generate
 * JavaBeans. In this case, it might not be possible to create an
 * object with all the correct state information solely from the class
 * name.
 *
 * @since 1.6
 */

public class CommandInfo {
    private String verb;
    private String className;

    /**
     * The Constructor for CommandInfo.
     * @param verb The command verb this CommandInfo decribes.
     * @param className The command's fully qualified class name.
     */
    public CommandInfo(String verb, String className) {
        this.verb = verb;
        this.className = className;
    }

    /**
     * Return the command verb.
     *
     * @return the command verb.
     */
    public String getCommandName() {
        return verb;
    }

    /**
     * Return the command's class name. <i>This method MAY return null in
     * cases where a CommandMap subclassed CommandInfo for its
     * own purposes.</i> In other words, it might not be possible to
     * create the correct state in the command by merely knowing
     * its class name. <b>DO NOT DEPEND ON THIS METHOD RETURNING
     * A VALID VALUE!</b>
     *
     * @return The class name of the command, or <i>null</i>
     */
    public String getCommandClass() {
        return className;
    }

    /**
     * Return the instantiated JavaBean component.
     * <p>
     * If {@code java.beans.Beans} is visible then it's
     * {@code java.beans.Beans#instantiate} method is invoked to instantiate
     * the component as a JavaBeans component.
     * When {@code java.beans.Beans} is not visible (when {@code java.desktop}
     * module is not  readable or when the runtime image does not contain the
     * {@code java.desktop} module) then the command's class is loaded and
     * instantiated with its public no-args constructor.
     * <p>
     * The component class needs to be public.
     * <p>
     * If the bean implements the {@code javax.activation.CommandObject}
     * interface, call its {@code setCommandContext} method.
     * <p>
     * If the DataHandler parameter is null, then the bean is
     * instantiated with no data. NOTE: this may be useful
     * if for some reason the DataHandler that is passed in
     * throws IOExceptions when this method attempts to
     * access its InputStream. It will allow the caller to
     * retrieve a reference to the bean if it can be
     * instantiated.
     * <p>
     * If the bean does NOT implement the CommandObject interface,
     * this method will check if it implements the
     * java.io.Externalizable interface. If it does, the bean's
     * readExternal method will be called if an InputStream
     * can be acquired from the DataHandler.<p>
     *
     * @param dh        The DataHandler that describes the data to be
     *                  passed to the command.
     * @param loader    The ClassLoader to be used to instantiate the bean.
     * @return The bean
     * @exception       IOException     for failures reading data
     * @exception       ClassNotFoundException  if command object class can't
     *                                          be found
     * @see java.beans.Beans#instantiate
     * @see javax.activation.CommandObject
     */
    public Object getCommandObject(DataHandler dh, ClassLoader loader)
                        throws IOException, ClassNotFoundException {
        Object new_bean = null;

        // try to instantiate the bean
        new_bean = Beans.instantiate(loader, className);

        // if we got one and it is a CommandObject
        if (new_bean != null) {
            if (new_bean instanceof CommandObject) {
                ((CommandObject)new_bean).setCommandContext(verb, dh);
            } else if (new_bean instanceof Externalizable) {
                if (dh != null) {
                    InputStream is = dh.getInputStream();
                    if (is != null) {
                        ((Externalizable)new_bean).readExternal(
                                               new ObjectInputStream(is));
                    }
                }
            }
        }

        return new_bean;
    }

    /**
     * Helper class to invoke Beans.instantiate reflectively or the equivalent
     * with core reflection when module java.desktop is not readable.
     */
    private static final class Beans {
        static final Method instantiateMethod;

        static {
            Method m;
            try {
                Class<?> c = Class.forName("java.beans.Beans");
                m = c.getDeclaredMethod("instantiate", ClassLoader.class, String.class);
            } catch (ClassNotFoundException e) {
                m = null;
            } catch (NoSuchMethodException e) {
                m = null;
            }
            instantiateMethod = m;
        }

        /**
         * Equivalent to invoking java.beans.Beans.instantiate(loader, cn)
         */
        static Object instantiate(ClassLoader loader, String cn)
                throws IOException, ClassNotFoundException {

            Exception exception;

            if (instantiateMethod != null) {

                // invoke Beans.instantiate
                try {
                    return instantiateMethod.invoke(null, loader, cn);
                } catch (InvocationTargetException e) {
                    exception = e;
                } catch (IllegalAccessException e) {
                    exception = e;
                }

            } else {

                SecurityManager security = System.getSecurityManager();
                if (security != null) {
                    // if it's ok with the SecurityManager, it's ok with me.
                    String cname = cn.replace('/', '.');
                    if (cname.startsWith("[")) {
                        int b = cname.lastIndexOf('[') + 2;
                        if (b > 1 && b < cname.length()) {
                            cname = cname.substring(b);
                        }
                    }
                    int i = cname.lastIndexOf('.');
                    if (i != -1) {
                        security.checkPackageAccess(cname.substring(0, i));
                    }
                }

                // Beans.instantiate specified to use SCL when loader is null
                if (loader == null) {
                    loader = (ClassLoader)
                        AccessController.doPrivileged(new PrivilegedAction() {
                            public Object run() {
                                ClassLoader cl = null;
                                try {
                                    cl = ClassLoader.getSystemClassLoader();
                                } catch (SecurityException ex) { }
                                return cl;
                            }
                        });
                }
                Class<?> beanClass = Class.forName(cn, false, loader);
                try {
                    return beanClass.getDeclaredConstructor().newInstance();
                } catch (Exception ex) {
                    throw new ClassNotFoundException(beanClass + ": " + ex, ex);
                }

            }
            return null;
        }
    }
}