/*

 * 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.

 *

 * 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 org.graalvm.compiler.replacements.classfile;

import java.io.DataInputStream;

import java.io.IOException;

import java.lang.reflect.Modifier;

import java.util.ArrayList;

import java.util.List;

import org.graalvm.compiler.replacements.classfile.ClassfileConstant.Utf8;

import jdk.vm.ci.meta.ResolvedJavaMethod;

import jdk.vm.ci.meta.ResolvedJavaType;

/**

 * Container for objects representing the {@code Code} attributes parsed from a class file.

 *

 * @see <a href="https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.3">Code

 *      attributes</a>

 * @see <a href="https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4">Constant

 *      Pool</a>

 */

public class Classfile {

    private final ResolvedJavaType type;

    private final List<ClassfileBytecode> codeAttributes;

    private static final int MAGIC = 0xCAFEBABE;

    /**

     * Creates a {@link Classfile} by parsing the class file bytes for {@code type} loadable from

     * {@code context}.

     *

     * @throws NoClassDefFoundError if there is an IO error while parsing the class file

     */

    public Classfile(ResolvedJavaType type, DataInputStream stream, ClassfileBytecodeProvider context) throws IOException {

        this.type = type;

        // magic

        int magic = stream.readInt();

        assert magic == MAGIC;

        int minor = stream.readUnsignedShort();

        int major = stream.readUnsignedShort();

            throw new UnsupportedClassVersionError("Unsupported class file version: " + major + "." + minor);

        }

        ClassfileConstantPool cp = new ClassfileConstantPool(stream, context);

        // access_flags, this_class, super_class

        skipFully(stream, 6);

        // interfaces

        skipFully(stream, stream.readUnsignedShort() * 2);

        // fields

        skipFields(stream);

        // methods

        codeAttributes = readMethods(stream, cp);

        // attributes

        skipAttributes(stream);

    }

    public ClassfileBytecode getCode(String name, String descriptor) {

        for (ClassfileBytecode code : codeAttributes) {

            ResolvedJavaMethod method = code.getMethod();

            if (method.getName().equals(name) && method.getSignature().toMethodDescriptor().equals(descriptor)) {

                return code;

            }

        }

        throw new NoSuchMethodError(type.toJavaName() + "." + name + descriptor);

    }

    private static void skipAttributes(DataInputStream stream) throws IOException {

        int attributesCount;

        attributesCount = stream.readUnsignedShort();

        for (int i = 0; i < attributesCount; i++) {

            skipFully(stream, 2); // name_index

            int attributeLength = stream.readInt();

            skipFully(stream, attributeLength);

        }

    }

    static void skipFully(DataInputStream stream, int n) throws IOException {

        long skipped = 0;

        do {

            long s = stream.skip(n - skipped);

            skipped += s;

            if (s == 0 && skipped != n) {

                // Check for EOF (i.e., truncated class file)

                if (stream.read() == -1) {

                    throw new IOException("truncated stream");

                }

                skipped++;

            }

        } while (skipped != n);

    }

    private ClassfileBytecode findCodeAttribute(DataInputStream stream, ClassfileConstantPool cp, String name, String descriptor, boolean isStatic) throws IOException {

        int attributesCount;

        attributesCount = stream.readUnsignedShort();

        ClassfileBytecode code = null;

        for (int i = 0; i < attributesCount; i++) {

            String attributeName = cp.get(Utf8.class, stream.readUnsignedShort()).value;

            int attributeLength = stream.readInt();

            if (code == null && attributeName.equals("Code")) {

                ResolvedJavaMethod method = cp.context.findMethod(type, name, descriptor, isStatic);

                // Even if we will discard the Code attribute (see below), we still

                // need to parse it to reach the following class file content.

                code = new ClassfileBytecode(method, stream, cp);

                if (method == null) {

                    // This is a method hidden from reflection

                    // (see sun.reflect.Reflection.filterMethods)

                    code = null;

                }

            } else {

                skipFully(stream, attributeLength);

            }

        }

        return code;

    }

    private static void skipFields(DataInputStream stream) throws IOException {

        int count = stream.readUnsignedShort();

        for (int i = 0; i < count; i++) {

            skipFully(stream, 6); // access_flags, name_index, descriptor_index

            skipAttributes(stream);

        }

    }

    private List<ClassfileBytecode> readMethods(DataInputStream stream, ClassfileConstantPool cp) throws IOException {

        int count = stream.readUnsignedShort();

        List<ClassfileBytecode> result = new ArrayList<>(count);

        for (int i = 0; i < count; i++) {

            int accessFlags = stream.readUnsignedShort();

            boolean isStatic = Modifier.isStatic(accessFlags);

            String name = cp.get(Utf8.class, stream.readUnsignedShort()).value;

            String descriptor = cp.get(Utf8.class, stream.readUnsignedShort()).value;

            ClassfileBytecode code = findCodeAttribute(stream, cp, name, descriptor, isStatic);

            if (code != null) {

                result.add(code);

            }

        }

        return result;

    }

    @Override

    public String toString() {

        return getClass().getSimpleName() + "<" + type.toJavaName() + ">";

    }

}