/*
 *  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.tomcat.util.bcel.classfile;

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

import org.apache.tomcat.util.bcel.Constants;

/**
 * Wrapper class that parses a given Java .class file. The method <A
 * href ="#parse">parse</A> returns a <A href ="JavaClass.html">
 * JavaClass</A> object on success. When an I/O error or an
 * inconsistency occurs an appropiate exception is propagated back to
 * the caller.
 *
 * The structure and the names comply, except for a few conveniences,
 * exactly with the <A href="ftp://java.sun.com/docs/specs/vmspec.ps">
 * JVM specification 1.0</a>. See this paper for
 * further details about the structure of a bytecode file.
 *
 * @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A> 
 */
public final class ClassParser {

    private static final int MAGIC = 0xCAFEBABE;

    private final DataInput file;
    private String class_name, superclass_name;
    private int access_flags; // Access rights of parsed class
    private String[] interface_names; // Names of implemented interfaces
    private ConstantPool constant_pool; // collection of constants
    private Annotations runtimeVisibleAnnotations; // "RuntimeVisibleAnnotations" attribute defined in the class
    private static final int BUFSIZE = 8192;

    private static final String[] INTERFACES_EMPTY_ARRAY = new String[0];

    /**
     * Parse class from the given stream.
     *
     * @param file Input stream
     */
    public ClassParser(InputStream file) {
        this.file = new FastDataInputStream(file, BUFSIZE);
    }


    /**
     * Parse the given Java class file and return an object that represents
     * the contained data, i.e., constants, methods, fields and commands.
     * A <em>ClassFormatException</em> is raised, if the file is not a valid
     * .class file. (This does not include verification of the byte code as it
     * is performed by the java interpreter).
     *
     * @return Class object representing the parsed class file
     * @throws  IOException
     * @throws  ClassFormatException
     */
    public JavaClass parse() throws IOException, ClassFormatException {
        /****************** Read headers ********************************/
        // Check magic tag of class file
        readID();
        // Get compiler version
        readVersion();
        /****************** Read constant pool and related **************/
        // Read constant pool entries
        readConstantPool();
        // Get class information
        readClassInfo();
        // Get interface information, i.e., implemented interfaces
        readInterfaces();
        /****************** Read class fields and methods ***************/
        // Read class fields, i.e., the variables of the class
        readFields();
        // Read class methods, i.e., the functions in the class
        readMethods();
        // Read class attributes
        readAttributes();

        // Return the information we have gathered in a new object
        return new JavaClass(class_name, superclass_name,
                access_flags, constant_pool, interface_names,
                runtimeVisibleAnnotations);
    }


    /**
     * Read information about the attributes of the class.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readAttributes() throws IOException, ClassFormatException {
        int attributes_count;
        attributes_count = file.readUnsignedShort();
        for (int i = 0; i < attributes_count; i++) {
            ConstantUtf8 c;
            String name;
            int name_index;
            int length;
            // Get class name from constant pool via `name_index' indirection
            name_index = file.readUnsignedShort();
            c = (ConstantUtf8) constant_pool.getConstant(name_index,
                    Constants.CONSTANT_Utf8);
            name = c.getBytes();
            // Length of data in bytes
            length = file.readInt();

            if (name.equals("RuntimeVisibleAnnotations")) {
                if (runtimeVisibleAnnotations != null) {
                    throw new ClassFormatException(
                            "RuntimeVisibleAnnotations attribute is not allowed more than once in a class file");
                }
                runtimeVisibleAnnotations = new Annotations(file, constant_pool);
            } else {
                // All other attributes are skipped
                Utility.skipFully(file, length);
            }
        }
    }


    /**
     * Read information about the class and its super class.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readClassInfo() throws IOException, ClassFormatException {
        access_flags = file.readUnsignedShort();
        /* Interfaces are implicitely abstract, the flag should be set
         * according to the JVM specification.
         */
        if ((access_flags & Constants.ACC_INTERFACE) != 0) {
            access_flags |= Constants.ACC_ABSTRACT;
        }
        if (((access_flags & Constants.ACC_ABSTRACT) != 0)
                && ((access_flags & Constants.ACC_FINAL) != 0)) {
            throw new ClassFormatException("Class can't be both final and abstract");
        }

        int class_name_index = file.readUnsignedShort();
        class_name = Utility.getClassName(constant_pool, class_name_index);

        int superclass_name_index = file.readUnsignedShort();
        if (superclass_name_index > 0) {
            // May be zero -> class is java.lang.Object
            superclass_name = Utility.getClassName(constant_pool, superclass_name_index);
        } else {
            superclass_name = "java.lang.Object";
        }
    }


    /**
     * Read constant pool entries.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readConstantPool() throws IOException, ClassFormatException {
        constant_pool = new ConstantPool(file);
    }


    /**
     * Read information about the fields of the class, i.e., its variables.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readFields() throws IOException, ClassFormatException {
        int fields_count = file.readUnsignedShort();
        for (int i = 0; i < fields_count; i++) {
            Utility.swallowFieldOrMethod(file);
        }
    }


    /******************** Private utility methods **********************/
    /**
     * Check whether the header of the file is ok.
     * Of course, this has to be the first action on successive file reads.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readID() throws IOException, ClassFormatException {
        if (file.readInt() != MAGIC) {
            throw new ClassFormatException("It is not a Java .class file");
        }
    }


    /**
     * Read information about the interfaces implemented by this class.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readInterfaces() throws IOException, ClassFormatException {
        int interfaces_count;
        interfaces_count = file.readUnsignedShort();
        if (interfaces_count > 0) {
            interface_names = new String[interfaces_count];
            for (int i = 0; i < interfaces_count; i++) {
                int index = file.readUnsignedShort();
                interface_names[i] = Utility.getClassName(constant_pool, index);
            }
        } else {
            interface_names = INTERFACES_EMPTY_ARRAY;
        }
    }


    /**
     * Read information about the methods of the class.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readMethods() throws IOException, ClassFormatException {
        int methods_count;
        methods_count = file.readUnsignedShort();
        for (int i = 0; i < methods_count; i++) {
            Utility.swallowFieldOrMethod(file);
        }
    }


    /**
     * Read major and minor version of compiler which created the file.
     * @throws  IOException
     * @throws  ClassFormatException
     */
    private void readVersion() throws IOException, ClassFormatException {
        // file.readUnsignedShort(); // Unused minor
        // file.readUnsignedShort(); // Unused major
        Utility.skipFully(file, 4);
    }
}