/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2005 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 org.mvel2.asm;

/**
 * A non standard class, field, method or code attribute.
 *
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

  /**
   * The type of this attribute.
   */
  public final String type;

  /**
   * The raw value of this attribute, used only for unknown attributes.
   */
  byte[] value;

  /**
   * The next attribute in this attribute list. May be <tt>null</tt>.
   */
  Attribute next;

  /**
   * Constructs a new empty attribute.
   *
   * @param type the type of the attribute.
   */
  protected Attribute(final String type) {
    this.type = type;
  }

  /**
   * Returns <tt>true</tt> if this type of attribute is unknown. The default
   * implementation of this method always returns <tt>true</tt>.
   *
   * @return <tt>true</tt> if this type of attribute is unknown.
   */
  public boolean isUnknown() {
    return true;
  }

  /**
   * Returns <tt>true</tt> if this type of attribute is a code attribute.
   *
   * @return <tt>true</tt> if this type of attribute is a code attribute.
   */
  public boolean isCodeAttribute() {
    return false;
  }

  /**
   * Returns the labels corresponding to this attribute.
   *
   * @return the labels corresponding to this attribute, or <tt>null</tt> if
   *         this attribute is not a code attribute that contains labels.
   */
  protected Label[] getLabels() {
    return null;
  }

  /**
   * Reads a {@link #type type} attribute. This method must return a <i>new</i>
   * {@link Attribute} object, of type {@link #type type}, corresponding to
   * the <tt>len</tt> bytes starting at the given offset, in the given class
   * reader.
   *
   * @param cr      the class that contains the attribute to be read.
   * @param off     index of the first byte of the attribute's content in {@link
   *                ClassReader#b cr.b}. The 6 attribute header bytes, containing the
   *                type and the length of the attribute, are not taken into account
   *                here.
   * @param len     the length of the attribute's content.
   * @param buf     buffer to be used to call
   *                {@link ClassReader#readUTF8 readUTF8},
   *                {@link ClassReader#readClass(int, char[]) readClass} or
   *                {@link ClassReader#readConst readConst}.
   * @param codeOff index of the first byte of code's attribute content in
   *                {@link ClassReader#b cr.b}, or -1 if the attribute to be read is
   *                not a code attribute. The 6 attribute header bytes, containing the
   *                type and the length of the attribute, are not taken into account
   *                here.
   * @param labels  the labels of the method's code, or <tt>null</tt> if the
   *                attribute to be read is not a code attribute.
   * @return a <i>new</i> {@link Attribute} object corresponding to the given
   *         bytes.
   */
  protected Attribute read(
      final ClassReader cr,
      final int off,
      final int len,
      final char[] buf,
      final int codeOff,
      final Label[] labels) {
    Attribute attr = new Attribute(type);
    attr.value = new byte[len];
    System.arraycopy(cr.b, off, attr.value, 0, len);
    return attr;
  }

  /**
   * Returns the byte array form of this attribute.
   *
   * @param cw        the class to which this attribute must be added. This parameter
   *                  can be used to add to the constant pool of this class the items
   *                  that corresponds to this attribute.
   * @param code      the bytecode of the method corresponding to this code
   *                  attribute, or <tt>null</tt> if this attribute is not a code
   *                  attributes.
   * @param len       the length of the bytecode of the method corresponding to this
   *                  code attribute, or <tt>null</tt> if this attribute is not a code
   *                  attribute.
   * @param maxStack  the maximum stack size of the method corresponding to
   *                  this code attribute, or -1 if this attribute is not a code
   *                  attribute.
   * @param maxLocals the maximum number of local variables of the method
   *                  corresponding to this code attribute, or -1 if this attribute is
   *                  not a code attribute.
   * @return the byte array form of this attribute.
   */
  protected ByteVector write(
      final ClassWriter cw,
      final byte[] code,
      final int len,
      final int maxStack,
      final int maxLocals) {
    ByteVector v = new ByteVector();
    v.data = value;
    v.length = value.length;
    return v;
  }

  /**
   * Returns the length of the attribute list that begins with this attribute.
   *
   * @return the length of the attribute list that begins with this attribute.
   */
  final int getCount() {
    int count = 0;
    Attribute attr = this;
    while (attr != null) {
      count += 1;
      attr = attr.next;
    }
    return count;
  }

  /**
   * Returns the size of all the attributes in this attribute list.
   *
   * @param cw        the class writer to be used to convert the attributes into byte
   *                  arrays, with the {@link #write write} method.
   * @param code      the bytecode of the method corresponding to these code
   *                  attributes, or <tt>null</tt> if these attributes are not code
   *                  attributes.
   * @param len       the length of the bytecode of the method corresponding to
   *                  these code attributes, or <tt>null</tt> if these attributes are
   *                  not code attributes.
   * @param maxStack  the maximum stack size of the method corresponding to
   *                  these code attributes, or -1 if these attributes are not code
   *                  attributes.
   * @param maxLocals the maximum number of local variables of the method
   *                  corresponding to these code attributes, or -1 if these attributes
   *                  are not code attributes.
   * @return the size of all the attributes in this attribute list. This size
   *         includes the size of the attribute headers.
   */
  final int getSize(
      final ClassWriter cw,
      final byte[] code,
      final int len,
      final int maxStack,
      final int maxLocals) {
    Attribute attr = this;
    int size = 0;
    while (attr != null) {
      cw.newUTF8(attr.type);
      size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
      attr = attr.next;
    }
    return size;
  }

  /**
   * Writes all the attributes of this attribute list in the given byte
   * vector.
   *
   * @param cw        the class writer to be used to convert the attributes into byte
   *                  arrays, with the {@link #write write} method.
   * @param code      the bytecode of the method corresponding to these code
   *                  attributes, or <tt>null</tt> if these attributes are not code
   *                  attributes.
   * @param len       the length of the bytecode of the method corresponding to
   *                  these code attributes, or <tt>null</tt> if these attributes are
   *                  not code attributes.
   * @param maxStack  the maximum stack size of the method corresponding to
   *                  these code attributes, or -1 if these attributes are not code
   *                  attributes.
   * @param maxLocals the maximum number of local variables of the method
   *                  corresponding to these code attributes, or -1 if these attributes
   *                  are not code attributes.
   * @param out       where the attributes must be written.
   */
  final void put(
      final ClassWriter cw,
      final byte[] code,
      final int len,
      final int maxStack,
      final int maxLocals,
      final ByteVector out) {
    Attribute attr = this;
    while (attr != null) {
      ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
      out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
      out.putByteArray(b.data, 0, b.length);
      attr = attr.next;
    }
  }
}
