/***
 * Copyright (c) 2000-2011 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package janala.instrument;


import java.io.IOException;
import java.io.InputStream;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;



/**
 * A ClassWriter that computes the common super class of two classes without
 * actually loading them with a ClassLoader.
 * 
 * @author Eric Bruneton
 */
public class SafeClassWriter extends ClassWriter {

    private final ClassLoader loader;

    
    public SafeClassWriter(ClassReader cr, ClassLoader loader, final int flags) {
        super(cr, flags);
        this.loader = loader != null ? loader : ClassLoader.getSystemClassLoader();
    }

    @Override
    protected String getCommonSuperClass(final String type1, final String type2) {
        try {
            ClassReader info1 = typeInfo(type1);
            ClassReader info2 = typeInfo(type2);
            if ((info1.getAccess() & Opcodes.ACC_INTERFACE) != 0) {
                if (typeImplements(type2, info2, type1)) {
                    return type1;
                } else {
                    return "java/lang/Object";
                }
            }
            if ((info2.getAccess() & Opcodes.ACC_INTERFACE) != 0) {
                if (typeImplements(type1, info1, type2)) {
                    return type2;
                } else {
                    return "java/lang/Object";
                }
            }
            StringBuilder b1 = typeAncestors(type1, info1);
            StringBuilder b2 = typeAncestors(type2, info2);
            String result = "java/lang/Object";
            int end1 = b1.length();
            int end2 = b2.length();
            while (true) {
                int start1 = b1.lastIndexOf(";", end1 - 1);
                int start2 = b2.lastIndexOf(";", end2 - 1);
                if (start1 != -1 && start2 != -1
                        && end1 - start1 == end2 - start2) {
                    String p1 = b1.substring(start1 + 1, end1);
                    String p2 = b2.substring(start2 + 1, end2);
                    if (p1.equals(p2)) {
                        result = p1;
                        end1 = start1;
                        end2 = start2;
                    } else {
                        return result;
                    }
                } else {
                    return result;
                }
            }
        } catch (IOException e) {
            throw new RuntimeException(e.toString());
        }
    }

    /**
     * Returns the internal names of the ancestor classes of the given type.
     * 
     * @param type
     *            the internal name of a class or interface.
     * @param info
     *            the ClassReader corresponding to 'type'.
     * @return a StringBuilder containing the ancestor classes of 'type',
     *         separated by ';'. The returned string has the following format:
     *         ";type1;type2 ... ;typeN", where type1 is 'type', and typeN is a
     *         direct subclass of Object. If 'type' is Object, the returned
     *         string is empty.
     * @throws IOException
     *             if the bytecode of 'type' or of some of its ancestor class
     *             cannot be loaded.
     */
    private StringBuilder typeAncestors(String type, ClassReader info)
            throws IOException {
        StringBuilder b = new StringBuilder();
        while (!"java/lang/Object".equals(type)) {
            b.append(';').append(type);
            type = info.getSuperName();
            info = typeInfo(type);
        }
        return b;
    }

    /**
     * Returns true if the given type implements the given interface.
     * 
     * @param type
     *            the internal name of a class or interface.
     * @param info
     *            the ClassReader corresponding to 'type'.
     * @param itf
     *            the internal name of a interface.
     * @return true if 'type' implements directly or indirectly 'itf'
     * @throws IOException
     *             if the bytecode of 'type' or of some of its ancestor class
     *             cannot be loaded.
     */
    private boolean typeImplements(String type, ClassReader info, String itf)
            throws IOException {
        while (!"java/lang/Object".equals(type)) {
            String[] itfs = info.getInterfaces();
            for (int i = 0; i < itfs.length; ++i) {
                if (itfs[i].equals(itf)) {
                    return true;
                }
            }
            for (int i = 0; i < itfs.length; ++i) {
                if (typeImplements(itfs[i], typeInfo(itfs[i]), itf)) {
                    return true;
                }
            }
            type = info.getSuperName();
            info = typeInfo(type);
        }
        return false;
    }

    /**
     * Returns a ClassReader corresponding to the given class or interface.
     * 
     * @param type
     *            the internal name of a class or interface.
     * @return the ClassReader corresponding to 'type'.
     * @throws IOException
     *             if the bytecode of 'type' cannot be loaded.
     */
    private ClassReader typeInfo(final String type) throws IOException {
        String resource = type + ".class";
        InputStream is = loader.getResourceAsStream(resource);
        if (is == null) {
            throw new IOException("Cannot create ClassReader for type " + type);
        }
        try {
            return new ClassReader(is);
        } finally {
            is.close();
        }
    }
}

