#include <stdio.h>

#include "ch32v003fun.h"
#include "modbus.h"
#include "rs485.h"
#include "shift_reg.h"
#include "simple_eeprom.h"
#include "state_manager.h"
#include "systick.h"

#define SLAVE_ADDRESS 0x01
#define MAX_MODBUS_FRAME 16
#define NUM_REGISTERS 1
#define FRAME_TIMEOUT_MS 4  // 3.5 char times at 9600 baud (~1.042ms per char)

static uint16_t holding_registers[NUM_REGISTERS];

static void handle_modbus_frame(uint8_t* rx_buffer, uint16_t rx_count) {
  uint8_t response[MAX_MODBUS_FRAME];
  uint16_t response_len;
  uint8_t result;

  result = modbus_process_message(rx_buffer, rx_count, SLAVE_ADDRESS,
                                  holding_registers, NUM_REGISTERS);

  if (result == MODBUS_ERROR_NONE) {
    shift_reg_write(holding_registers[0]);
    save_state(holding_registers[0]);

    response_len = modbus_create_response(response, SLAVE_ADDRESS,
                                          MODBUS_FC_WRITE_SINGLE_REGISTER, 0,
                                          holding_registers[0]);
  } else {
    response_len = modbus_create_error_response(
        response, SLAVE_ADDRESS, MODBUS_FC_WRITE_SINGLE_REGISTER, result);
  }

  rs485_send(response, response_len);
}

int main(void) {
  uint8_t rx_buffer[MAX_MODBUS_FRAME];
  uint16_t rx_count = 0;
  uint32_t last_byte_time = 0;

  SystemInit();
  systick_init();
  shift_reg_init();
  rs485_init(UART_BRR);

  // restore last saved state
  holding_registers[0] = load_state();
  shift_reg_write(holding_registers[0]);

  while (1) {
    if (!rs485_available()) {
      continue;
    }

    uint32_t current_time = millis();

    // check for frame timeout
    if (rx_count > 0 && (current_time - last_byte_time) > FRAME_TIMEOUT_MS) {
      rx_count = 0;
    }

    rx_buffer[rx_count++] = rs485_read();
    last_byte_time = current_time;

    // process complete frame
    if (rx_count >= 8) {
      handle_modbus_frame(rx_buffer, rx_count);
      rx_count = 0;
    }

    // buffer overflow protection
    if (rx_count >= MAX_MODBUS_FRAME) {
      rx_count = 0;
    }
  }
}