#ifndef MODBUS_TCP_H
#define MODBUS_TCP_H

#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>

#include "modbus_memory.h"

#define MODBUS_TCP_PORT 502

/* MBAP header is always 7 bytes */
#define MODBUS_TCP_MBAP_LEN 7

/* Maximum Modbus TCP ADU size:
 * 7-byte MBAP + up to 253-byte PDU = 260 bytes
 */
#define MODBUS_TCP_MAX_ADU_LEN 260
#define MODBUS_TCP_MAX_PDU_LEN 253

/* Modbus exception codes */
#define MODBUS_EX_ILLEGAL_FUNCTION      0x01
#define MODBUS_EX_ILLEGAL_DATA_ADDRESS  0x02
#define MODBUS_EX_ILLEGAL_DATA_VALUE    0x03
#define MODBUS_EX_SERVER_DEVICE_FAILURE 0x04

/* Supported function codes */
#define MODBUS_FC_READ_COILS               0x01
#define MODBUS_FC_READ_DISCRETE_INPUTS     0x02
#define MODBUS_FC_READ_HOLDING_REGISTERS   0x03
#define MODBUS_FC_READ_INPUT_REGISTERS     0x04
#define MODBUS_FC_WRITE_SINGLE_COIL        0x05
#define MODBUS_FC_WRITE_SINGLE_REGISTER    0x06
#define MODBUS_FC_WRITE_MULTIPLE_COILS     0x0F
#define MODBUS_FC_WRITE_MULTIPLE_REGISTERS 0x10

typedef struct
{
    uint16_t transaction_id;
    uint16_t protocol_id;
    uint16_t length;
    uint8_t unit_id;
} modbus_mbap_t;

/*
 * Process one Modbus TCP request ADU and write the response ADU.
 *
 * mem           = target virtual device memory
 * req           = incoming request bytes
 * req_len       = number of request bytes
 * resp          = output response buffer
 * resp_max_len  = size of resp buffer
 * resp_len      = actual response length written
 *
 * Returns true if a response was built successfully.
 * Returns false on malformed packet / buffer issues.
 */
bool modbus_tcp_process_request(modbus_memory_t *mem,
                                const uint8_t *req,
                                size_t req_len,
                                uint8_t *resp,
                                size_t resp_max_len,
                                size_t *resp_len);

#endif /* MODBUS_TCP_H */