package de.fub.bytecode.generic;

import java.io.*;
import de.fub.bytecode.util.ByteSequence;
import de.fub.bytecode.Constants;
import de.fub.bytecode.classfile.*;

/** 
 * Abstract super class for instructions that use an index into the 
 * constant pool such as LDC, INVOKEVIRTUAL, etc.
 *
 * @see ConstantPoolGen
 * @see LDC
 * @see INVOKEVIRTUAL
 *
 * @version $Id: CPInstruction.java,v 1.6 2001/07/03 08:20:18 dahm Exp $
 * @author  <A HREF="http://www.berlin.de/~markus.dahm/">M. Dahm</A>
 */
public abstract class CPInstruction extends Instruction
  implements TypedInstruction, IndexedInstruction
{
  protected int index; // index to constant pool

  /**
   * Empty constructor needed for the Class.newInstance() statement in
   * Instruction.readInstruction(). Not to be used otherwise.
   */
  CPInstruction() {}

  /**
   * @param index to constant pool
   */
  protected CPInstruction(short opcode, int index) {
    super(opcode, (short)3);
    setIndex(index);
  }

  /**
   * Dump instruction as byte code to stream out.
   * @param out Output stream
   */
  public void dump(DataOutputStream out) throws IOException {
    out.writeByte(opcode);
    out.writeShort(index);
  }

  /**
   * Long output format:
   *
   * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]" 
   * "("&lt;length of instruction&gt;")" "&lt;"&lt; constant pool index&gt;"&gt;"
   *
   * @param verbose long/short format switch
   * @return mnemonic for instruction
   */
  public String toString(boolean verbose) {
    return super.toString(verbose) + " " + index;
  }

  /**
   * @return mnemonic for instruction with symbolic references resolved
   */
  public String toString(ConstantPool cp) {
    Constant c   = cp.getConstant(index);
    String   str = cp.constantToString(c);

    if(c instanceof ConstantClass)
      str = str.replace('.', '/');

    return de.fub.bytecode.Constants.OPCODE_NAMES[opcode] + " " + str;
  }

  /**
   * Read needed data (i.e., index) from file.
   * @param bytes input stream
   * @param wide wide prefix?
   */
  protected void initFromFile(ByteSequence bytes, boolean wide)
       throws IOException
  {
    setIndex(bytes.readUnsignedShort());
    length = 3;
  }

  /**
   * @return index in constant pool referred by this instruction.
   */
  public final int getIndex() { return index; }

  /**
   * Set the index to constant pool.
   * @param index in  constant pool.
   */
  public void setIndex(int index) { 
    if(index < 0)
      throw new ClassGenException("Negative index value: " + index);

    this.index = index;
  }

  /** @return type related with this instruction.
   */
  public Type getType(ConstantPoolGen cpg) {
    ConstantPool cp   = cpg.getConstantPool();
    String       name = cp.getConstantString(index, de.fub.bytecode.Constants.CONSTANT_Class);

    if(!name.startsWith("["))
      name = "L" + name + ";";

    return Type.getType(name);
  }
}