#pragma once

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

// Simple Modbus RTU master focused on function 0x03 (Read Holding Registers).
// Transport is byte-stream oriented (USB-serial in this project).

typedef struct {
  uint8_t slave_id;
  bool disable_crc;
} modbus_rtu_master_config_t;

typedef struct {
  modbus_rtu_master_config_t cfg;

  // RX accumulation
  uint8_t rx_buf[256];
  size_t rx_len;

  // Pending request tracking
  bool awaiting_response;
  uint32_t request_started_ms;
  uint16_t expected_byte_count;
} modbus_rtu_master_t;

void modbus_rtu_master_init(modbus_rtu_master_t *m, modbus_rtu_master_config_t cfg);

// Builds a Read Holding Registers (0x03) request.
// Returns frame length.
size_t modbus_rtu_build_read_holding(uint8_t *out, size_t out_cap,
                                    uint8_t slave_id, uint16_t start_addr, uint16_t quantity,
                                    bool disable_crc);

// Feed received bytes into the Modbus parser.
void modbus_rtu_feed(modbus_rtu_master_t *m, const uint8_t *data, size_t len);

// Returns true when a full response for function 0x03 is present in rx_buf.
// If true, `*out_data_offset` points to first data byte, `*out_word_count` is number of 16-bit registers.
bool modbus_rtu_try_parse_read_holding_response(modbus_rtu_master_t *m,
                                               uint8_t expected_slave_id,
                                               uint16_t expected_quantity,
                                               size_t *out_data_offset,
                                               uint16_t *out_word_count);

uint16_t modbus_rtu_get_u16_be(const uint8_t *p);
uint16_t modbus_rtu_crc16(const uint8_t *data, size_t len);

float modbus_float_dcba(uint16_t w1, uint16_t w2);