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/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package com.feilong.lib.javassist.tools;

import java.util.HashMap;
import java.util.Map;
import java.util.UUID;

import com.feilong.lib.javassist.CannotCompileException;
import com.feilong.lib.javassist.CtBehavior;

/**
 * Creates bytecode that when executed calls back to the instance's result method.
 *
 * 
 * Example of how to create and insert a callback:
 * 
 * 
 *  * ctMethod.insertAfter(new Callback("Thread.currentThread()"){
 * 
 *     public void result(Object[] objects){
 *         Thread thread = (Thread) objects[0];
 *         // do something with thread...
 *     }
 * }.sourceCode());
 * 
 * 
 * Contains utility methods for inserts callbacks in CtBehaviour, example:
 * 
 * 
 *  * insertAfter(ctBehaviour, new Callback("Thread.currentThread(), dummyString"){
 * 
 *     public void result(Object[] objects){
 *         Thread thread = (Thread) objects[0];
 *         // do something with thread...
 *     }
 * });
 * 
 *
 * @author Marten Hedborg
 * @author Shigeru Chiba
 */
public abstract class Callback{

    public static Map callbacks = new HashMap<>();

    private final String                sourceCode;

    /**
     * Constructs a new Callback object.
     *
     * @param src
     *            The source code representing the inserted callback bytecode.
     *            Can be one or many single statements each returning one object.
     *            If many single statements are used they must be comma separated.
     */
    public Callback(String src){
        String uuid = UUID.randomUUID().toString();
        callbacks.put(uuid, this);
        sourceCode = "((javassist.tools.Callback) javassist.tools.Callback.callbacks.get(\"" + uuid + "\")).result(new Object[]{" + src
                        + "});";
    }

    /**
     * Gets called when bytecode is executed
     *
     * @param objects
     *            Objects that the bytecode in callback returns
     */
    public abstract void result(Object[] objects);

    @Override
    public String toString(){
        return sourceCode();
    }

    public String sourceCode(){
        return sourceCode;
    }

    /**
     * Utility method to insert callback at the beginning of the body.
     *
     * @param callback
     *            The callback
     *
     * @see CtBehavior#insertBefore(String)
     */
    public static void insertBefore(CtBehavior behavior,Callback callback) throws CannotCompileException{
        behavior.insertBefore(callback.toString());
    }

    /**
     * Utility method to inserts callback at the end of the body.
     * The callback is inserted just before every return instruction.
     * It is not executed when an exception is thrown.
     *
     * @param behavior
     *            The behaviour to insert callback in
     * @param callback
     *            The callback
     *
     * @see CtBehavior#insertAfter(String, boolean)
     */
    public static void insertAfter(CtBehavior behavior,Callback callback) throws CannotCompileException{
        behavior.insertAfter(callback.toString(), false);
    }

    /**
     * Utility method to inserts callback at the end of the body.
     * The callback is inserted just before every return instruction.
     * It is not executed when an exception is thrown.
     *
     * @param behavior
     *            The behaviour to insert callback in
     * @param callback
     *            The callback representing the inserted.
     * @param asFinally
     *            True if the inserted is executed
     *            Not only when the control normally returns
     *            but also when an exception is thrown.
     *            If this parameter is true, the inserted code cannot
     *            access local variables.
     *
     * @see CtBehavior#insertAfter(String, boolean)
     */
    public static void insertAfter(CtBehavior behavior,Callback callback,boolean asFinally) throws CannotCompileException{
        behavior.insertAfter(callback.toString(), asFinally);
    }

    /**
     * Utility method to inserts callback at the specified line in the body.
     *
     * @param behavior
     *            The behaviour to insert callback in
     * @param callback
     *            The callback representing.
     * @param lineNum
     *            The line number. The callback is inserted at the
     *            beginning of the code at the line specified by this
     *            line number.
     *
     * @return The line number at which the callback has been inserted.
     *
     * @see CtBehavior#insertAt(int, String)
     */
    public static int insertAt(CtBehavior behavior,Callback callback,int lineNum) throws CannotCompileException{
        return behavior.insertAt(lineNum, callback.toString());
    }
}