/*
 * Usurpataion --- client-server protocol interface.
 *
 * Copyright (C) 2019 Ramūnas Mažeikis
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; version 2.1
 * of the License.
 *
 * This program 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

#ifndef PROTOCOL_H_INCLUDED
#define PROTOCOL_H_INCLUDED

#include <errno.h>

#define	E_TLV_OVERFLOW		(1 << 0)
#define E_UNKNOWN_TYPE		(1 << 1)
#define E_IVALID_DESCRIPTOR	(1 << 2)

/**
 * Regular packets contain tlv's defined by tlv_type.
 *
 * Hearbeat packet tell daemon that device is still alive and listening.
 *
 * Discovery packets are used for what they say.
 */
enum packet_type {
	REGURAL,
	HEARTBEAT,
	DISCOVERY
};

/**
 * Message sequence number since beggining of sesssion.
 *
 * Mainly used for identifying lost messages.
 */
typedef unsigned int msg_idx_t;

enum tlv_type {
	/**
	 * NULL-terminated string. To be put in a queue to display on the
	 * screen.
	 */
	TEXT,

	/** Fixed point. 1 decimal digit of precision. */
	FPI1,

	/** Literally time_t */
	TIMESTAMP,

	/** Represents a request for lost message. Data is unsigned integer
	 * that uniquely identifies the message.
	 */
	REQUEST,

	/**
	 * Response to request. Begins with unsigned integer that represents
	 * which message is being repeated and the actual null-terminated
	 * message after that.
	 */
	REPLY,

	/**
	 * UUID that represents a particular device.
	 */
	UUID
};

/**
 * Packet data itself is a special type of tlv. A packet is either regular,
 * hearbeat or discovery.
 *
 * May be used to send data.
 */
struct tlv_packet {
	enum packet_type type;
	size_t size;
	size_t offset;
	char *data;	/* Bytes representing tlv's */
};

/**
 * Literally type-length-value
 * */
struct tlv {
	enum tlv_type type;
	size_t length;
	void *data;
};

struct tlv_parser {
	char *data;
	size_t offset;
	size_t size;
};

int get_tlv(struct tlv_parser *parser, struct tlv *ret);

/**
 * Appends data to the next packet to be sent. Type of data is determined by
 * enum tlv_type.
 * */
int push_data(struct tlv_packet *packet, enum tlv_type type, char *data);

void clear_data(struct tlv_packet *packet);

size_t tlv_data_size(struct tlv_parser *parser);

#endif /* PROTOCOL_H_INCLUDED */