/* Software Name : AsmDex
 * Version : 1.0
 *
 * Copyright © 2012 France Télécom
 * 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.ow2.asmdex.instruction;

import org.ow2.asmdex.lowLevelUtils.ByteVector;
import org.ow2.asmdex.lowLevelUtils.IDalvikValueReader;
import org.ow2.asmdex.structureCommon.Label;
import org.ow2.asmdex.structureWriter.ConstantPool;

/**
 * Encodes and decodes an instruction built with the Dalvik format 20T.
 * 
 * @author Julien Névo
 */
public class InstructionFormat20T extends Instruction implements IOffsetInstruction {

	private static final int INSTRUCTION_SIZE = 4; // Instruction size in bytes.
	
	private int offset;
	
	/**
	 * Offset in bytes of the instruction from the beginning of the method.
	 */
	private int instructionOffset;
	
	/**
	 * Return the offset pointing to the beginning of the branch, from the start of the Dex file.
	 * @return the offset pointing to the beginning of the branch, from the start of the Dex file.
	 */
	@Override
	public int getOffset() {
		return offset;
	}
	
	/**
	 * Label to which to jump.
	 */
	private Label label;
	
	/**
	 * Returns the label to which the instruction jumps.
	 * @return the label to which the instruction jumps.
	 */
	@Override
	public Label getLabel() { return label; }
	
	/**
	 * Constructor of the Instruction, using a Reader to parse its bytecode.
	 * @param reader reader on the Instruction to parse, pointing after the 16-bit opcode.
	 * @param opcode 16-bit opcode.
	 */
//	public InstructionFormat20T(IDalvikValueReader reader, int opcode) {
//		super(opcode);
//		
//		// The format is 00|op AAAA.
//		int readOffset = reader.sshort() * 2; // * 2 because branch offsets are word based.
//		// Offset points to the beginning of the branch, from the start of the Dex file.
//		// It is related to the current opcode (hence the -4).
//		offset = reader.getPos() - 4 + readOffset;
//	}
	
	/**
	 * Returns the Offset encoded in the given 16-bit opcode. <i>It must be performed only once after
	 * having read the opcode.</i>
	 * @param reader reader on the Instruction to parse, pointing after the 16-bit opcode.
	 * @param opcode the 16-bit opcode.
	 * @return the Offset from the beginning of the Dex file.
	 */
	public static int getOffset(IDalvikValueReader reader, int opcode) {
		// The format is 00|op AAAA.
		int readOffset = reader.sshort() * 2; // * 2 because branch offsets are word based.
		// Offset points to the beginning of the branch, from the start of the Dex file.
		// It is related to the current opcode (hence the -4).
		return reader.getPos() - 4 + readOffset;
	}

	/**
	 * Skips the data of this Instruction.
	 * @param reader reader on the Instruction to parse, pointing after the 16-bit opcode.
	 */
	public static void skip(IDalvikValueReader reader) {
		reader.relativeSeek(INSTRUCTION_SIZE - 2); // The first word has already been read.
	}
	
	/**
	 * Constructor of the Instruction by providing all the elements it's composed of.
	 * @param opcode 8 or 16 bits opcode.
	 * @param label Label to which is linked this Instruction.
	 * @param instructionOffset offset of this Instruction from the beginning of its Method.
	 */
	public InstructionFormat20T(int opcode, Label label, int instructionOffset) {
		super(opcode);
		
		this.label = label;
		this.instructionOffset = instructionOffset;
	}

	@Override
	public int getSize() {
		return INSTRUCTION_SIZE;
	}
	
//	@Override
//	public int[] getUsedRegisters() {
//		return null;
//	}

//	@Override
//	public int getNbEncodedRegisters() {
//		return 0;
//	}

	@Override
	public int getInstructionOffset() {
		return instructionOffset;
	}
	
	@Override
	public void setInstructionOffset(int instructionOffset) {
		this.instructionOffset = instructionOffset;
	};
	
	@Override
	public void write(ByteVector out, ConstantPool constantPool) {
		// The format is 00|op AAAA.
		out.putShort(opcodeByte);
		out.putShort((label.getOffset() - instructionOffset) / 2); // / 2 because offsets are word-based.
	}

}