TLVPacket.java

package com.o3dr.services.android.lib.drone.companion.solo.tlv;

import android.os.Parcel;
import android.os.Parcelable;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * All communication follows this TLV format in little endian.
 */
public abstract class TLVPacket implements Parcelable {

    public static final int MIN_TLV_PACKET_SIZE = 4 + 4; //4 bytes for the message type and 4 bytes for the message length.
    public static final ByteOrder TLV_BYTE_ORDER = ByteOrder.LITTLE_ENDIAN;

    private final int messageType;
    private final int messageLength;

    private final ByteBuffer byteBuffer;

    public TLVPacket(int type, int length){
        this.messageType = type;
        this.messageLength = length;

        byteBuffer = ByteBuffer.allocate(MIN_TLV_PACKET_SIZE + messageLength);
        byteBuffer.order(TLV_BYTE_ORDER);
    }

    public final int getMessageType() {
        return messageType;
    }

    public final int getMessageLength() {
        return messageLength;
    }

    public final byte[] toBytes(){
        byteBuffer.clear();

        byteBuffer.putInt(this.messageType);
        byteBuffer.putInt(this.messageLength);

        getMessageValue(byteBuffer);

        final byte[] bytes = new byte[byteBuffer.position()];
        byteBuffer.rewind();
        byteBuffer.get(bytes);

        return bytes;
    }

    @Override
    public String toString() {
        return "TLVPacket{" +
                "messageLength=" + messageLength +
                ", messageType=" + messageType +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof TLVPacket)) return false;

        TLVPacket tlvPacket = (TLVPacket) o;

        if (messageType != tlvPacket.messageType) return false;
        return messageLength == tlvPacket.messageLength;

    }

    @Override
    public int hashCode() {
        int result = messageType;
        result = 31 * result + messageLength;
        return result;
    }

    protected abstract void getMessageValue(ByteBuffer valueCarrier);

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(this.messageType);
        dest.writeInt(this.messageLength);
    }

    protected TLVPacket(Parcel in) {
        this(in.readInt(), in.readInt());
    }
}