/*
    * Copyright  2000-2004 The Apache Software Foundation
    *
    *  Licensed 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.bcel.generic;
  
  import java.io.DataOutputStream;
  import java.io.IOException;
  import org.apache.bcel.util.ByteSequence;
  
  /*** 
   * Abstract super class for branching instructions like GOTO, IFEQ, etc..
   * Branch instructions may have a variable length, namely GOTO, JSR, 
   * LOOKUPSWITCH and TABLESWITCH.
   *
   * @see InstructionList
   * @version $Id: BranchInstruction.java 386056 2006-03-15 11:31:56Z tcurdt $
   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
   */
  public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
  
      protected int index; // Branch target relative to this instruction
      protected InstructionHandle target; // Target object in instruction list
      protected int position; // Byte code offset
  
  
      /***
       * Empty constructor needed for the Class.newInstance() statement in
       * Instruction.readInstruction(). Not to be used otherwise.
       */
      BranchInstruction() {
      }
  
  
      /*** Common super constructor
       * @param opcode Instruction opcode
       * @param target instruction to branch to
       */
      protected BranchInstruction(short opcode, InstructionHandle target) {
          super(opcode, (short) 3);
          setTarget(target);
      }
  
  
      /***
       * Dump instruction as byte code to stream out.
       * @param out Output stream
       */
      public void dump( DataOutputStream out ) throws IOException {
          out.writeByte(opcode);
          index = getTargetOffset();
          if (Math.abs(index) >= 32767) {
              throw new ClassGenException("Branch target offset too large for short");
          }
          out.writeShort(index); // May be negative, i.e., point backwards
      }
  
  
      /***
       * @param _target branch target
       * @return the offset to  `target' relative to this instruction
       */
      protected int getTargetOffset( InstructionHandle _target ) {
          if (_target == null) {
              throw new ClassGenException("Target of " + super.toString(true)
                      + " is invalid null handle");
          }
          int t = _target.getPosition();
          if (t < 0) {
              throw new ClassGenException("Invalid branch target position offset for "
                      + super.toString(true) + ":" + t + ":" + _target);
          }
          return t - position;
      }
  
  
      /***
       * @return the offset to this instruction's target
       */
      protected int getTargetOffset() {
          return getTargetOffset(target);
      }
  
  
      /***
       * 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 ) {
         position += offset;
         return 0;
     }
 
 
     /***
      * Long output format:
      *
      * &lt;position in byte code&gt;
      * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]" 
      * "("&lt;length of instruction&gt;")"
      * "&lt;"&lt;target instruction&gt;"&gt;" "@"&lt;branch target offset&gt;
      *
      * @param verbose long/short format switch
      * @return mnemonic for instruction
      */
     public String toString( boolean verbose ) {
         String s = super.toString(verbose);
         String t = "null";
         if (verbose) {
             if (target != null) {
                 if (target.getInstruction() == this) {
                     t = "<points to itself>";
                 } else if (target.getInstruction() == null) {
                     t = "<null instruction!!!?>";
                 } else {
                     t = target.getInstruction().toString(false); // Avoid circles
                 }
             }
         } else {
             if (target != null) {
                 index = getTargetOffset();
                 t = "" + (index + position);
             }
         }
         return s + " -> " + t;
     }
 
 
     /***
      * Read needed data (e.g. index) from file. Conversion to a InstructionHandle
      * is done in InstructionList(byte[]).
      *
      * @param bytes input stream
      * @param wide wide prefix?
      * @see InstructionList
      */
     protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException {
         length = 3;
         index = bytes.readShort();
     }
 
 
     /***
      * @return target offset in byte code
      */
     public final int getIndex() {
         return index;
     }
 
 
     /***
      * @return target of branch instruction
      */
     public InstructionHandle getTarget() {
         return target;
     }
 
 
     /***
      * Set branch target
      * @param target branch target
      */
     public void setTarget( InstructionHandle target ) {
         notifyTarget(this.target, target, this);
         this.target = target;
     }
 
 
     /***
      * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen
      */
     static final void notifyTarget( InstructionHandle old_ih, InstructionHandle new_ih,
             InstructionTargeter t ) {
         if (old_ih != null) {
             old_ih.removeTargeter(t);
         }
         if (new_ih != null) {
             new_ih.addTargeter(t);
         }
     }
 
 
     /***
      * @param old_ih old target
      * @param new_ih new target
      */
     public void updateTarget( InstructionHandle old_ih, InstructionHandle new_ih ) {
         if (target == old_ih) {
             setTarget(new_ih);
         } else {
             throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
         }
     }
 
 
     /***
      * @return true, if ih is target of this instruction
      */
     public boolean containsTarget( InstructionHandle ih ) {
         return (target == ih);
     }
 
 
     /***
      * Inform target that it's not targeted anymore.
      */
     void dispose() {
         setTarget(null);
         index = -1;
         position = -1;
     }
 }