#include "modbus_rtu_slave.h"

#include <string.h>

/* Modbus RTU最大ADU为256字节。 */
#define MODBUS_RTU_ADU_SIZE_MAX          256U

/*
 * 当前串口为115200 bit/s。Modbus规范建议波特率高于19200时，
 * 帧间隔固定使用1.75ms，这里向上取整为2ms。
 */
#define MODBUS_RTU_FRAME_GAP_MS          2U

#define MODBUS_BROADCAST_ADDRESS         0U

#define MODBUS_FC_READ_COILS             0x01U
#define MODBUS_FC_READ_HOLDING_REGS      0x03U
#define MODBUS_FC_WRITE_SINGLE_REG       0x06U
#define MODBUS_FC_WRITE_MULTIPLE_COILS   0x0FU
#define MODBUS_FC_WRITE_MULTIPLE_REGS    0x10U

#define MODBUS_EX_ILLEGAL_FUNCTION       0x01U
#define MODBUS_EX_ILLEGAL_ADDRESS        0x02U
#define MODBUS_EX_ILLEGAL_VALUE          0x03U

#define MODBUS_READ_COILS_MAX            2000U
#define MODBUS_READ_REGS_MAX             125U
#define MODBUS_WRITE_COILS_MAX           1968U
#define MODBUS_WRITE_REGS_MAX            123U

static UART_HandleTypeDef *s_uart;
static uint8_t s_slave_address;

/*
 * DMA缓冲区只由DMA写入；帧缓冲区在接收回调中完成一次快照，
 * 随后由任务解析，避免DMA重启后覆盖尚未处理的数据。
 */
static uint8_t s_rx_dma_buffer[MODBUS_RTU_ADU_SIZE_MAX];
static uint8_t s_rx_frame[MODBUS_RTU_ADU_SIZE_MAX];
static uint8_t s_tx_frame[MODBUS_RTU_ADU_SIZE_MAX];

static volatile uint16_t s_rx_frame_length;
static volatile uint8_t s_rx_frame_ready;
static volatile uint8_t s_tx_busy;
static volatile uint32_t s_rx_event_tick;
static volatile uint32_t s_last_valid_frame_tick;
static volatile uint8_t s_has_received_valid_frame;

/* 10000个保持寄存器占20KB；10000个线圈按位存储，占1250字节。 */
static uint16_t s_holding_registers[MODBUS_MAP_ITEM_COUNT];
static uint8_t s_coils[(MODBUS_MAP_ITEM_COUNT + 7U) / 8U];

volatile ModbusSlaveStats g_modbus_slave_stats;

static uint16_t Modbus_Crc16(const uint8_t *data, uint16_t length)
{
  uint16_t crc = 0xFFFFU;
  uint16_t index;
  uint8_t bit;

  for (index = 0U; index < length; index++)
  {
    crc ^= data[index];

    for (bit = 0U; bit < 8U; bit++)
    {
      if ((crc & 0x0001U) != 0U)
      {
        crc = (uint16_t)((crc >> 1U) ^ 0xA001U);
      }
      else
      {
        crc >>= 1U;
      }
    }
  }

  return crc;
}

static uint16_t Modbus_GetU16Be(const uint8_t *data)
{
  return (uint16_t)(((uint16_t)data[0] << 8U) | data[1]);
}

static uint8_t Modbus_AddressRangeIsValid(uint16_t start, uint16_t quantity)
{
  if ((quantity == 0U) || (start >= MODBUS_MAP_ITEM_COUNT))
  {
    return 0U;
  }

  /* 先做减法再比较，避免start + quantity发生16位溢出。 */
  return (quantity <= (MODBUS_MAP_ITEM_COUNT - start)) ? 1U : 0U;
}

static uint8_t Modbus_CoilGetUnchecked(uint16_t address)
{
  uint8_t mask = (uint8_t)(1U << (address & 0x0007U));

  return ((s_coils[address >> 3U] & mask) != 0U) ? 1U : 0U;
}

static void Modbus_CoilSetUnchecked(uint16_t address, uint8_t state)
{
  uint8_t mask = (uint8_t)(1U << (address & 0x0007U));

  if (state != 0U)
  {
    s_coils[address >> 3U] |= mask;
  }
  else
  {
    s_coils[address >> 3U] &= (uint8_t)(~mask);
  }
}

static HAL_StatusTypeDef Modbus_StartReceive(void)
{
  HAL_StatusTypeDef status;

  if ((s_uart == NULL) || (s_tx_busy != 0U))
  {
    return HAL_BUSY;
  }

  status = HAL_UARTEx_ReceiveToIdle_DMA(s_uart,
                                        s_rx_dma_buffer,
                                        sizeof(s_rx_dma_buffer));

  if ((status == HAL_OK) && (s_uart->hdmarx != NULL))
  {
    /*
     * 普通Modbus帧只应在IDLE或缓冲区满时交给应用。
     * 关闭DMA半传输中断，避免长帧在一半位置被误认为完整帧。
     */
    __HAL_DMA_DISABLE_IT(s_uart->hdmarx, DMA_IT_HT);
  }

  return status;
}

static void Modbus_StopReceive(void)
{
  if (s_uart != NULL)
  {
    (void)HAL_UART_AbortReceive(s_uart);
  }
}

static void Modbus_AppendCrc(uint8_t *frame, uint16_t payload_length)
{
  uint16_t crc = Modbus_Crc16(frame, payload_length);

  /* Modbus RTU在线路上传输CRC低字节在前、高字节在后。 */
  frame[payload_length] = (uint8_t)(crc & 0x00FFU);
  frame[payload_length + 1U] = (uint8_t)(crc >> 8U);
}

static uint16_t Modbus_BuildException(uint8_t function, uint8_t exception)
{
  s_tx_frame[0] = s_slave_address;
  s_tx_frame[1] = (uint8_t)(function | 0x80U);
  s_tx_frame[2] = exception;
  Modbus_AppendCrc(s_tx_frame, 3U);

  return 5U;
}

static uint16_t Modbus_ProcessReadCoils(const uint8_t *request,
                                        uint16_t request_length)
{
  uint16_t start;
  uint16_t quantity;
  uint16_t index;
  uint8_t byte_count;

  if (request_length != 8U)
  {
    g_modbus_slave_stats.illegal_value_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  start = Modbus_GetU16Be(&request[2]);
  quantity = Modbus_GetU16Be(&request[4]);

  if ((quantity == 0U) || (quantity > MODBUS_READ_COILS_MAX))
  {
    g_modbus_slave_stats.illegal_value_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  if (Modbus_AddressRangeIsValid(start, quantity) == 0U)
  {
    g_modbus_slave_stats.illegal_address_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_ADDRESS);
  }

  byte_count = (uint8_t)((quantity + 7U) / 8U);
  s_tx_frame[0] = s_slave_address;
  s_tx_frame[1] = MODBUS_FC_READ_COILS;
  s_tx_frame[2] = byte_count;
  (void)memset(&s_tx_frame[3], 0, byte_count);

  /* Modbus规定请求的第一个线圈放在响应数据首字节的最低位。 */
  for (index = 0U; index < quantity; index++)
  {
    if (Modbus_CoilGetUnchecked((uint16_t)(start + index)) != 0U)
    {
      s_tx_frame[3U + (index >> 3U)] |=
        (uint8_t)(1U << (index & 0x0007U));
    }
  }

  Modbus_AppendCrc(s_tx_frame, (uint16_t)(3U + byte_count));
  return (uint16_t)(5U + byte_count);
}

static uint16_t Modbus_ProcessReadHolding(const uint8_t *request,
                                          uint16_t request_length)
{
  uint16_t start;
  uint16_t quantity;
  uint16_t index;
  uint16_t value;

  if (request_length != 8U)
  {
    g_modbus_slave_stats.illegal_value_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  start = Modbus_GetU16Be(&request[2]);
  quantity = Modbus_GetU16Be(&request[4]);

  if ((quantity == 0U) || (quantity > MODBUS_READ_REGS_MAX))
  {
    g_modbus_slave_stats.illegal_value_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  if (Modbus_AddressRangeIsValid(start, quantity) == 0U)
  {
    g_modbus_slave_stats.illegal_address_count++;
    return Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_ADDRESS);
  }

  s_tx_frame[0] = s_slave_address;
  s_tx_frame[1] = MODBUS_FC_READ_HOLDING_REGS;
  s_tx_frame[2] = (uint8_t)(quantity * 2U);

  for (index = 0U; index < quantity; index++)
  {
    value = s_holding_registers[start + index];
    s_tx_frame[3U + index * 2U] = (uint8_t)(value >> 8U);
    s_tx_frame[4U + index * 2U] = (uint8_t)(value & 0x00FFU);
  }

  Modbus_AppendCrc(s_tx_frame, (uint16_t)(3U + quantity * 2U));
  return (uint16_t)(5U + quantity * 2U);
}

static uint16_t Modbus_ProcessWriteSingleRegister(const uint8_t *request,
                                                   uint16_t request_length,
                                                   uint8_t is_broadcast)
{
  uint16_t address;
  uint16_t value;

  if (request_length != 8U)
  {
    g_modbus_slave_stats.illegal_value_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  address = Modbus_GetU16Be(&request[2]);
  value = Modbus_GetU16Be(&request[4]);

  if (address >= MODBUS_MAP_ITEM_COUNT)
  {
    g_modbus_slave_stats.illegal_address_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_ADDRESS);
  }

  s_holding_registers[address] = value;

  if (is_broadcast != 0U)
  {
    return 0U;
  }

  /* 0x06的正常响应必须原样回显请求的前6个字节。 */
  (void)memcpy(s_tx_frame, request, 6U);
  Modbus_AppendCrc(s_tx_frame, 6U);
  return 8U;
}

static uint16_t Modbus_ProcessWriteMultipleCoils(const uint8_t *request,
                                                 uint16_t request_length,
                                                 uint8_t is_broadcast)
{
  uint16_t start;
  uint16_t quantity;
  uint16_t index;
  uint8_t byte_count;
  uint8_t expected_byte_count;

  if (request_length < 9U)
  {
    g_modbus_slave_stats.illegal_value_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  start = Modbus_GetU16Be(&request[2]);
  quantity = Modbus_GetU16Be(&request[4]);
  byte_count = request[6];
  expected_byte_count = (uint8_t)((quantity + 7U) / 8U);

  if ((quantity == 0U) ||
      (quantity > MODBUS_WRITE_COILS_MAX) ||
      (byte_count != expected_byte_count) ||
      (request_length != (uint16_t)(9U + byte_count)))
  {
    g_modbus_slave_stats.illegal_value_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  if (Modbus_AddressRangeIsValid(start, quantity) == 0U)
  {
    g_modbus_slave_stats.illegal_address_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_ADDRESS);
  }

  for (index = 0U; index < quantity; index++)
  {
    Modbus_CoilSetUnchecked((uint16_t)(start + index),
      (uint8_t)((request[7U + (index >> 3U)] >> (index & 0x0007U)) & 0x01U));
  }

  if (is_broadcast != 0U)
  {
    return 0U;
  }

  s_tx_frame[0] = s_slave_address;
  s_tx_frame[1] = MODBUS_FC_WRITE_MULTIPLE_COILS;
  (void)memcpy(&s_tx_frame[2], &request[2], 4U);
  Modbus_AppendCrc(s_tx_frame, 6U);
  return 8U;
}

static uint16_t Modbus_ProcessWriteMultipleRegisters(const uint8_t *request,
                                                     uint16_t request_length,
                                                     uint8_t is_broadcast)
{
  uint16_t start;
  uint16_t quantity;
  uint16_t index;
  uint8_t byte_count;

  if (request_length < 9U)
  {
    g_modbus_slave_stats.illegal_value_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  start = Modbus_GetU16Be(&request[2]);
  quantity = Modbus_GetU16Be(&request[4]);
  byte_count = request[6];

  if ((quantity == 0U) ||
      (quantity > MODBUS_WRITE_REGS_MAX) ||
      (byte_count != (uint8_t)(quantity * 2U)) ||
      (request_length != (uint16_t)(9U + byte_count)))
  {
    g_modbus_slave_stats.illegal_value_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_VALUE);
  }

  if (Modbus_AddressRangeIsValid(start, quantity) == 0U)
  {
    g_modbus_slave_stats.illegal_address_count++;
    return (is_broadcast != 0U) ? 0U :
      Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_ADDRESS);
  }

  for (index = 0U; index < quantity; index++)
  {
    s_holding_registers[start + index] =
      Modbus_GetU16Be(&request[7U + index * 2U]);
  }

  if (is_broadcast != 0U)
  {
    return 0U;
  }

  s_tx_frame[0] = s_slave_address;
  s_tx_frame[1] = MODBUS_FC_WRITE_MULTIPLE_REGS;
  (void)memcpy(&s_tx_frame[2], &request[2], 4U);
  Modbus_AppendCrc(s_tx_frame, 6U);
  return 8U;
}

static uint16_t Modbus_ProcessRequest(const uint8_t *request,
                                      uint16_t request_length)
{
  uint16_t calculated_crc;
  uint16_t received_crc;
  uint8_t is_broadcast;

  if (request_length < 4U)
  {
    return 0U;
  }

  calculated_crc = Modbus_Crc16(request, (uint16_t)(request_length - 2U));
  received_crc = (uint16_t)(request[request_length - 2U] |
                   ((uint16_t)request[request_length - 1U] << 8U));

  if (calculated_crc != received_crc)
  {
    g_modbus_slave_stats.crc_error_count++;
    return 0U;
  }

  if ((request[0] != s_slave_address) &&
      (request[0] != MODBUS_BROADCAST_ADDRESS))
  {
    g_modbus_slave_stats.ignored_address_count++;
    return 0U;
  }

  is_broadcast = (request[0] == MODBUS_BROADCAST_ADDRESS) ? 1U : 0U;
  g_modbus_slave_stats.valid_frame_count++;
  s_last_valid_frame_tick = HAL_GetTick();
  s_has_received_valid_frame = 1U;

  switch (request[1])
  {
    case MODBUS_FC_READ_COILS:
      /* 广播请求不允许读取，从站不作响应。 */
      return (is_broadcast != 0U) ? 0U :
        Modbus_ProcessReadCoils(request, request_length);

    case MODBUS_FC_READ_HOLDING_REGS:
      return (is_broadcast != 0U) ? 0U :
        Modbus_ProcessReadHolding(request, request_length);

    case MODBUS_FC_WRITE_SINGLE_REG:
      return Modbus_ProcessWriteSingleRegister(request,
                                               request_length,
                                               is_broadcast);

    case MODBUS_FC_WRITE_MULTIPLE_COILS:
      return Modbus_ProcessWriteMultipleCoils(request,
                                              request_length,
                                              is_broadcast);

    case MODBUS_FC_WRITE_MULTIPLE_REGS:
      return Modbus_ProcessWriteMultipleRegisters(request,
                                                  request_length,
                                                  is_broadcast);

    default:
      g_modbus_slave_stats.illegal_function_count++;
      return (is_broadcast != 0U) ? 0U :
        Modbus_BuildException(request[1], MODBUS_EX_ILLEGAL_FUNCTION);
  }
}

HAL_StatusTypeDef ModbusSlave_Init(UART_HandleTypeDef *huart,
                                   uint8_t slave_address)
{
  if ((huart == NULL) ||
      (slave_address == MODBUS_BROADCAST_ADDRESS) ||
      (slave_address > 247U))
  {
    return HAL_ERROR;
  }

  s_uart = huart;
  s_slave_address = slave_address;
  s_rx_frame_length = 0U;
  s_rx_frame_ready = 0U;
  s_tx_busy = 0U;
  s_has_received_valid_frame = 0U;

  (void)memset(s_holding_registers, 0, sizeof(s_holding_registers));
  (void)memset(s_coils, 0, sizeof(s_coils));
  (void)memset((void *)&g_modbus_slave_stats, 0,
               sizeof(g_modbus_slave_stats));

  s_holding_registers[HMI_REG_DEVICE_ID] = 0xF407U;

  return Modbus_StartReceive();
}

void ModbusSlave_Poll(void)
{
  uint16_t response_length;

  if ((s_rx_frame_ready == 0U) || (s_tx_busy != 0U))
  {
    return;
  }

  /*
   * IDLE事件在约1个字符静默后产生；再等待到2ms，
   * 满足当前115200波特率下的Modbus RTU帧间隔要求。
   */
  if ((HAL_GetTick() - s_rx_event_tick) < MODBUS_RTU_FRAME_GAP_MS)
  {
    return;
  }

  response_length = Modbus_ProcessRequest(s_rx_frame, s_rx_frame_length);

  if (response_length > 0U)
  {
    /*
     * 发送期间停止接收，避免自动收发电路可能产生的本机回波
     * 被误当成下一条主站请求。
     */
    Modbus_StopReceive();
    s_tx_busy = 1U;

    if (HAL_UART_Transmit_DMA(s_uart, s_tx_frame, response_length) == HAL_OK)
    {
      g_modbus_slave_stats.tx_frame_count++;
    }
    else
    {
      s_tx_busy = 0U;
      g_modbus_slave_stats.uart_error_count++;
      (void)Modbus_StartReceive();
    }
  }

  /*
   * 处理期间保持ready=1，使中断不会覆盖当前帧；
   * 到这里再释放帧槽。
   */
  s_rx_frame_ready = 0U;
}

void ModbusSlave_OnRxEvent(UART_HandleTypeDef *huart, uint16_t size)
{
  if ((huart != s_uart) || (s_uart == NULL))
  {
    return;
  }

  g_modbus_slave_stats.rx_event_count++;

  if ((size > 0U) && (size <= MODBUS_RTU_ADU_SIZE_MAX))
  {
    if (s_rx_frame_ready == 0U)
    {
      (void)memcpy(s_rx_frame, s_rx_dma_buffer, size);
      s_rx_frame_length = size;
      s_rx_event_tick = HAL_GetTick();
      s_rx_frame_ready = 1U;
    }
    else
    {
      /* 单帧槽尚未处理完成，丢弃新帧而不覆盖旧帧。 */
      g_modbus_slave_stats.dropped_frame_count++;
    }
  }
  else
  {
    g_modbus_slave_stats.dropped_frame_count++;
  }

  /* DMA普通模式在IDLE事件后已经停止，需要显式重新启动。 */
  if (s_tx_busy == 0U)
  {
    (void)Modbus_StartReceive();
  }
}

void ModbusSlave_OnTxComplete(UART_HandleTypeDef *huart)
{
  if ((huart != s_uart) || (s_uart == NULL))
  {
    return;
  }

  s_tx_busy = 0U;
  (void)Modbus_StartReceive();
}

void ModbusSlave_OnUartError(UART_HandleTypeDef *huart)
{
  if ((huart != s_uart) || (s_uart == NULL))
  {
    return;
  }

  g_modbus_slave_stats.uart_error_count++;
  s_tx_busy = 0U;
  (void)HAL_UART_Abort(huart);
  (void)Modbus_StartReceive();
}

uint8_t ModbusSlave_SetHoldingRegister(uint16_t address, uint16_t value)
{
  if (address >= MODBUS_MAP_ITEM_COUNT)
  {
    return 0U;
  }

  s_holding_registers[address] = value;
  return 1U;
}

uint8_t ModbusSlave_GetHoldingRegister(uint16_t address, uint16_t *value)
{
  if ((address >= MODBUS_MAP_ITEM_COUNT) || (value == NULL))
  {
    return 0U;
  }

  *value = s_holding_registers[address];
  return 1U;
}

uint8_t ModbusSlave_SetCoil(uint16_t address, uint8_t state)
{
  if (address >= MODBUS_MAP_ITEM_COUNT)
  {
    return 0U;
  }

  Modbus_CoilSetUnchecked(address, state);
  return 1U;
}

uint8_t ModbusSlave_GetCoil(uint16_t address, uint8_t *state)
{
  if ((address >= MODBUS_MAP_ITEM_COUNT) || (state == NULL))
  {
    return 0U;
  }

  *state = Modbus_CoilGetUnchecked(address);
  return 1U;
}

uint8_t ModbusSlave_IsConnected(uint32_t timeout_ms)
{
  if (s_has_received_valid_frame == 0U)
  {
    return 0U;
  }

  return ((HAL_GetTick() - s_last_valid_frame_tick) <= timeout_ms) ? 1U : 0U;
}