/*

 * reserved comment block

 * DO NOT REMOVE OR ALTER!

 */

package com.sun.org.apache.bcel.internal.generic;

/* ====================================================================

 * The Apache Software License, Version 1.1

 *

 * Copyright (c) 2001 The Apache Software Foundation.  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.

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 *    notice, this list of conditions and the following disclaimer in

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 *    distribution.

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 * 3. The end-user documentation included with the redistribution,

 *    if any, must include the following acknowledgment:

 *       "This product includes software developed by the

 *        Apache Software Foundation (http://www.apache.org/)."

 *    Alternately, this acknowledgment may appear in the software itself,

 *    if and wherever such third-party acknowledgments normally appear.

 *

 * 4. The names "Apache" and "Apache Software Foundation" and

 *    "Apache BCEL" must not be used to endorse or promote products

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 *    written permission, please contact apache@apache.org.

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 * SUCH DAMAGE.

 * ====================================================================

 *

 * This software consists of voluntary contributions made by many

 * individuals on behalf of the Apache Software Foundation.  For more

 * information on the Apache Software Foundation, please see

 * <http://www.apache.org/>.

 */

import com.sun.org.apache.bcel.internal.classfile.Utility;

import java.util.HashSet;

import java.util.Collection;

import java.util.HashMap;

/**

 * Instances of this class give users a handle to the instructions contained in

 * an InstructionList. Instruction objects may be used more than once within a

 * list, this is useful because it saves memory and may be much faster.

 *

 * Within an InstructionList an InstructionHandle object is wrapped

 * around all instructions, i.e., it implements a cell in a

 * doubly-linked list. From the outside only the next and the

 * previous instruction (handle) are accessible. One

 * can traverse the list via an Enumeration returned by

 * InstructionList.elements().

 *

 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>

 * @see Instruction

 * @see BranchHandle

 * @see InstructionList

 */

public class InstructionHandle implements java.io.Serializable {

  InstructionHandle next, prev;  // Will be set from the outside

  Instruction       instruction;

  protected int     i_position = -1; // byte code offset of instruction

  private HashSet   targeters;

  private HashMap   attributes;

  public final InstructionHandle getNext()        { return next; }

  public final InstructionHandle getPrev()        { return prev; }

  public final Instruction       getInstruction() { return instruction; }

  /**

   * Replace current instruction contained in this handle.

   * Old instruction is disposed using Instruction.dispose().

   */

  public void setInstruction(Instruction i) { // Overridden in BranchHandle

    if(i == null)

      throw new ClassGenException("Assigning null to handle");

    if((this.getClass() != BranchHandle.class) && (i instanceof BranchInstruction))

      throw new ClassGenException("Assigning branch instruction " + i + " to plain handle");

    if(instruction != null)

      instruction.dispose();

    instruction = i;

  }

  /**

   * Temporarily swap the current instruction, without disturbing

   * anything. Meant to be used by a debugger, implementing

   * breakpoints. Current instruction is returned.

   */

  public Instruction swapInstruction(Instruction i) {

    Instruction oldInstruction = instruction;

    instruction = i;

    return oldInstruction;

  }

  /*private*/ protected InstructionHandle(Instruction i) {

    setInstruction(i);

  }

  private static InstructionHandle ih_list = null; // List of reusable handles

  /** Factory method.

   */

  static final InstructionHandle getInstructionHandle(Instruction i) {

    if(ih_list == null)

      return new InstructionHandle(i);

    else {

      InstructionHandle ih = ih_list;

      ih_list = ih.next;

      ih.setInstruction(i);

      return ih;

    }

  }

  /**

   * Called by InstructionList.setPositions when setting the position for every

   * instruction. In the presence of variable length instructions `setPositions()'

   * performs multiple passes over the instruction list to calculate the

   * correct (byte) positions and offsets by calling this function.

   *

   * @param offset additional offset caused by preceding (variable length) instructions

   * @param max_offset the maximum offset that may be caused by these instructions

   * @return additional offset caused by possible change of this instruction's length

   */

  protected int updatePosition(int offset, int max_offset) {

    i_position += offset;

    return 0;

  }

  /** @return the position, i.e., the byte code offset of the contained

   * instruction. This is accurate only after

   * InstructionList.setPositions() has been called.

   */

  public int getPosition() { return i_position; }

  /** Set the position, i.e., the byte code offset of the contained

   * instruction.

   */

  void setPosition(int pos) { i_position = pos; }

  /** Overridden in BranchHandle

   */

  protected void addHandle() {

    next    = ih_list;

    ih_list = this;

  }

  /**

   * Delete contents, i.e., remove user access and make handle reusable.

   */

  void dispose() {

    next = prev = null;

    instruction.dispose();

    instruction = null;

    i_position = -1;

    attributes = null;

    removeAllTargeters();

    addHandle();

  }

  /** Remove all targeters, if any.

   */

  public void removeAllTargeters() {

    if(targeters != null)

      targeters.clear();

  }

  /**

   * Denote this handle isn't referenced anymore by t.

   */

  public void removeTargeter(InstructionTargeter t) {

    targeters.remove(t);

  }

  /**

   * Denote this handle is being referenced by t.

   */

  public void addTargeter(InstructionTargeter t) {

    if(targeters == null)

      targeters = new HashSet();

    //if(!targeters.contains(t))

    targeters.add(t);

  }

  public boolean hasTargeters() {

    return (targeters != null) && (targeters.size() > 0);

  }

  /**

   * @return null, if there are no targeters

   */

  public InstructionTargeter[] getTargeters() {

    if(!hasTargeters())

      return null;

    InstructionTargeter[] t = new InstructionTargeter[targeters.size()];

    targeters.toArray(t);

    return t;

  }

  /** @return a (verbose) string representation of the contained instruction.

   */

  public String toString(boolean verbose) {

    return Utility.format(i_position, 4, false, ' ') + ": " + instruction.toString(verbose);

  }

  /** @return a string representation of the contained instruction.

   */

  public String toString() {

    return toString(true);

  }

  /** Add an attribute to an instruction handle.

   *

   * @param key the key object to store/retrieve the attribute

   * @param attr the attribute to associate with this handle

   */

  public void addAttribute(Object key, Object attr) {

    if(attributes == null)

      attributes = new HashMap(3);

    attributes.put(key, attr);

  }

  /** Delete an attribute of an instruction handle.

   *

   * @param key the key object to retrieve the attribute

   */

  public void removeAttribute(Object key) {

    if(attributes != null)

      attributes.remove(key);

  }

  /** Get attribute of an instruction handle.

   *

   * @param key the key object to store/retrieve the attribute

   */

  public Object getAttribute(Object key) {

    if(attributes != null)

      return attributes.get(key);

    return null;

  }

  /** @return all attributes associated with this handle

   */

  public Collection getAttributes() {

    return attributes.values();

  }

  /** Convenience method, simply calls accept() on the contained instruction.

   *

   * @param v Visitor object

   */

  public void accept(Visitor v) {

    instruction.accept(v);

  }

}