/**
 *
 */
package org.rs2.janus.net.packet;

import org.jboss.netty.buffer.ChannelBuffer;

/**
 * @author Michael Schmidt <H3llKing> <msrsps@hotmail.com>
 *
 */
public class PacketReader {

    /**
     * The buffer the is wrapped by this reader.
     */
    private final ChannelBuffer internalBuffer;

    /**
     * If the reader is in bit access.
     */
    private boolean bitAccess = false;

    /**
     * The bit position of the reader.
     */
    private int bitPosition;

    /**
     * New instance
     *
     * @param packet
     *            The packet who's payload will be read.
     */
    public PacketReader(Packet packet) {
        this.internalBuffer = packet.getPayload();
    }

    /**
     *
     */
    public int readBit() {
        int bytePos = bitPosition >> 3;
        int bitOffset = 8 - (bitPosition & 7);

        return (internalBuffer.getByte(bytePos) & PacketConstants.BIT_MASK[bitOffset]) << bitOffset;
    }

    /**
     * Puts the reader into bit access and sets the bit fields.
     */
    public void setBitAccess() {
        if (bitAccess == true)
            throw new IllegalStateException("Already in bit access.");

        bitAccess = true;
        bitPosition = internalBuffer.readerIndex() << 3;
    }

    /**
     * Puts the reader into byte access and resets the bit fields.
     */
    public void setByteAccess() {
        if (bitAccess == false)
            throw new IllegalStateException("Already in byte access.");

        int bytePos = bitPosition >> 3;

        if (bitPosition % 8 != 0) // Round as needed.
            ++bytePos;

        internalBuffer.readerIndex(bytePos);
        bitPosition = 0;
    }

}