/*
 * $Id: PrintLiteralInstruction.java 536 2008-02-19 06:03:27Z weiju $
 * 
 * Created on 10/06/2005
 * Copyright 2005-2008 by Wei-ju Wu
 * This file is part of The Z-machine Preservation Project (ZMPP).
 *
 * ZMPP is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ZMPP is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ZMPP.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.zmpp.instructions;

import org.zmpp.base.Memory;
import org.zmpp.vm.Machine;

/**
 * This class implements the print and print_ret instructions.
 *
 * @author Wei-ju Wu
 * @version 1.0
 */
public class PrintLiteralInstruction extends AbstractInstruction {

    /**
     * The instruction address.
     */
    private int instructionAddress;

    /**
     * Memory access object.
     */
    private Memory memory;

    /**
     * Constructor.
     *
     * @param machineState the machine state reference
     * @param opcode the opcode
     * @param memory the Memory object
     * @param instrAddress the instruction address
     */
    public PrintLiteralInstruction(Machine machineState, int opcode,
            Memory memory, int instrAddress) {
        super(machineState, opcode);
        this.memory = memory;
        instructionAddress = instrAddress;
    }

    /**
     * {@inheritDoc}
     */
    protected String getOperandString() {

        final String str
                = getMachine().getGameData().getZCharDecoder().decode2Zscii(memory,
                        instructionAddress + 1, 0).toString();
        return "\"" + str + "\"";
    }

    /**
     * {@inheritDoc}
     */
    public InstructionForm getInstructionForm() {

        return InstructionForm.SHORT;
    }

    /**
     * {@inheritDoc}
     */
    public OperandCount getOperandCount() {

        return OperandCount.C0OP;
    }

    /**
     * {@inheritDoc}
     */
    public void setLength(final int length) {

        // overridden to do nothing
    }

    /**
     * {@inheritDoc}
     */
    public int getLength() {

        return getLiteralLengthInBytes() + 1;
    }

    /**
     * {@inheritDoc}
     */
    protected InstructionStaticInfo getStaticInfo() {

        return PrintLiteralStaticInfo.getInstance();
    }

    /**
     * {@inheritDoc}
     */
    public void doInstruction() {

        if (getOpcode() == PrintLiteralStaticInfo.OP_PRINT_RET) {

            getMachine().getOutput().printZString(instructionAddress + 1);
            getMachine().getOutput().newline();
            returnFromRoutine(TRUE);

        } else if (getOpcode() == PrintLiteralStaticInfo.OP_PRINT) {

            getMachine().getOutput().printZString(instructionAddress + 1);
            nextInstruction();

        } else {

            throwInvalidOpcode();
        }
    }

    /**
     * Returns the address of the literal.
     *
     * @return the address of the literal
     */
    public int getLiteralAddress() {

        return instructionAddress + 1;
    }

    /**
     * Determines the byte length of the ZSCII string literal.
     *
     * @return the length of the literal in bytes
     */
    private int getLiteralLengthInBytes() {

        int currentAddress = instructionAddress + 1;
        int zword = 0;

        do {

            zword = memory.readUnsignedShort(currentAddress);
            currentAddress += 2;

        } while ((zword & 0x8000) == 0);

        return currentAddress - (instructionAddress + 1);
    }
}