#include "modbus_master.h"

#include "debug.h"
#include "rs485.h"
#include "systick.h"

static uint16_t modbus_crc16(const unsigned char* buf, unsigned int len) {
  static const uint16_t table[256] = {
      0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241, 0xC601,
      0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440, 0xCC01, 0x0CC0,
      0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40, 0x0A00, 0xCAC1, 0xCB81,
      0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841, 0xD801, 0x18C0, 0x1980, 0xD941,
      0x1B00, 0xDBC1, 0xDA81, 0x1A40, 0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01,
      0x1DC0, 0x1C80, 0xDC41, 0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0,
      0x1680, 0xD641, 0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081,
      0x1040, 0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
      0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441, 0x3C00,
      0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41, 0xFA01, 0x3AC0,
      0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840, 0x2800, 0xE8C1, 0xE981,
      0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41, 0xEE01, 0x2EC0, 0x2F80, 0xEF41,
      0x2D00, 0xEDC1, 0xEC81, 0x2C40, 0xE401, 0x24C0, 0x2580, 0xE541, 0x2700,
      0xE7C1, 0xE681, 0x2640, 0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0,
      0x2080, 0xE041, 0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281,
      0x6240, 0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
      0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41, 0xAA01,
      0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840, 0x7800, 0xB8C1,
      0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41, 0xBE01, 0x7EC0, 0x7F80,
      0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40, 0xB401, 0x74C0, 0x7580, 0xB541,
      0x7700, 0xB7C1, 0xB681, 0x7640, 0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101,
      0x71C0, 0x7080, 0xB041, 0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0,
      0x5280, 0x9241, 0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481,
      0x5440, 0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
      0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841, 0x8801,
      0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40, 0x4E00, 0x8EC1,
      0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41, 0x4400, 0x84C1, 0x8581,
      0x4540, 0x8701, 0x47C0, 0x4680, 0x8641, 0x8201, 0x42C0, 0x4380, 0x8341,
      0x4100, 0x81C1, 0x8081, 0x4040};

  uint8_t xor = 0;
  uint16_t crc = 0xFFFF;

  while (len--) {
    xor = (*buf++) ^ crc;
    crc >>= 8;
    crc ^= table[xor];
  }

  return crc;
}

static inline uint16_t mb_word(uint8_t hi, uint8_t lo) {
  return ((uint16_t)hi << 8) | lo;
}

static inline void mb_split(uint16_t val, uint8_t* hi, uint8_t* lo) {
  *hi = (val >> 8) & 0xFF;
  *lo = val & 0xFF;
}

uint16_t modbus_create_request(uint8_t* req, uint8_t slave_addr,
                               uint8_t function, uint16_t address,
                               uint16_t value) {
  req[0] = slave_addr;
  req[1] = function;

  uint8_t hi, lo;
  mb_split(address, &hi, &lo);
  req[2] = hi;
  req[3] = lo;

  if (function == MODBUS_FC_WRITE_SINGLE_REGISTER) {
    mb_split(value, &hi, &lo);
    req[4] = hi;
    req[5] = lo;

    // add crc
    uint16_t crc = modbus_crc16(req, 6);
    req[6] = crc & 0xFF;
    req[7] = (crc >> 8) & 0xFF;
    return 8;
  } else if (function == MODBUS_FC_READ_HOLDING_REGISTERS) {
    mb_split(value, &hi, &lo);  // value = number of registers to read
    req[4] = hi;
    req[5] = lo;

    // add crc
    uint16_t crc = modbus_crc16(req, 6);
    req[6] = crc & 0xFF;
    req[7] = (crc >> 8) & 0xFF;
    return 8;
  }

  return 0;
}

uint8_t modbus_process_response(uint8_t* buf, uint16_t len, uint16_t* value) {
  if (len < MB_MIN_LEN) {
    return MODBUS_ERROR_VALUE;
  }

  // check for error response
  if (buf[1] & 0x80) {
    return buf[2];
  }

  // verify crc
  uint16_t rcv_crc = mb_word(buf[len - 1], buf[len - 2]);
  uint16_t calc_crc = modbus_crc16(buf, len - 2);

  if (rcv_crc != calc_crc) {
    return MODBUS_ERROR_VALUE;
  }

  switch (buf[1]) {
    case MODBUS_FC_WRITE_SINGLE_REGISTER:
      if (len != MB_WREG_LEN) {
        return MODBUS_ERROR_VALUE;
      }
      *value = mb_word(buf[4], buf[5]);
      break;

    case MODBUS_FC_READ_HOLDING_REGISTERS:
      if (len < 5) {
        return MODBUS_ERROR_VALUE;
      }
      uint8_t byte_count = buf[2];
      for (uint8_t i = 0; i < byte_count / 2; i++) {
        value[i] = mb_word(buf[3 + i * 2], buf[4 + i * 2]);
      }
      break;

    default:
      return MODBUS_ERROR_FUNCTION;
  }

  return MODBUS_ERROR_NONE;
}

void modbus_init(modbus_context_t* ctx,
                 void (*response_callback)(uint8_t*, uint16_t, uint16_t),
                 void (*error_callback)(uint8_t)) {
  while (rs485_available()) {
    uint8_t byte = rs485_read();
    DEBUG_PRINT("Flushed stale byte: 0x%02X\n", byte);
  }

  ctx->state = MODBUS_IDLE;
  ctx->last_send_time = 0;
  ctx->response_timeout = 100;  // Default 100ms timeout
  ctx->rx_len = 0;
  ctx->current_bit = 1;
  ctx->last_value = 0;
  ctx->on_response = response_callback;
  ctx->on_error = error_callback;
}

void modbus_set_timeout(modbus_context_t* ctx, uint32_t timeout_ms) {
  ctx->response_timeout = timeout_ms;
}

uint8_t modbus_send_request(modbus_context_t* ctx, uint8_t slave_addr,
                            uint8_t function, uint16_t address,
                            uint16_t value) {
  if (ctx->state != MODBUS_IDLE) {
    return 0;  // Busy
  }

  uint16_t len =
      modbus_create_request(ctx->buffer, slave_addr, function, address, value);
  rs485_send(ctx->buffer, len);

  ctx->last_send_time = millis();
  ctx->rx_len = 0;
  ctx->state = MODBUS_WAITING_RESPONSE;

  return 1;  // Success
}

void modbus_process(modbus_context_t* ctx) {
  uint32_t current_time = millis();

  switch (ctx->state) {
    case MODBUS_IDLE:
      break;

    case MODBUS_WAITING_RESPONSE:
      // Check for timeout
      if (current_time - ctx->last_send_time >= ctx->response_timeout) {
        DEBUG_PRINT("Timeout after %lu ms with %d bytes received",
                    current_time - ctx->last_send_time, ctx->rx_len);
        if (ctx->on_error) {
          ctx->on_error(MODBUS_ERROR_TIMEOUT);
        }
        ctx->state = MODBUS_IDLE;
        break;
      }

      // Read available data
      while (rs485_available() && ctx->rx_len < sizeof(ctx->buffer)) {
        ctx->buffer[ctx->rx_len++] = rs485_read();
        // DEBUG_PRINT("Received byte: 0x%02X\n", ctx->buffer[ctx->rx_len - 1]);

        if (ctx->rx_len >= MB_MIN_LEN) {
          // holding reg
          if (ctx->buffer[1] == MODBUS_FC_READ_HOLDING_REGISTERS) {
            if (ctx->rx_len >= 3 && ctx->rx_len >= (3 + ctx->buffer[2] + 2)) {
              ctx->state = MODBUS_PROCESS_RESPONSE;
              break;
            }
          }

          // single reg w
          else if (ctx->buffer[1] == MODBUS_FC_WRITE_SINGLE_REGISTER) {
            if (ctx->rx_len >= MB_WREG_LEN) {
              ctx->state = MODBUS_PROCESS_RESPONSE;
              break;
            }
          }

          else if (ctx->buffer[1] & 0x80) {
            if (ctx->rx_len >= 5) {  // err 5b
              ctx->state = MODBUS_PROCESS_RESPONSE;
              break;
            }
          }
        }
      }
      break;

    case MODBUS_PROCESS_RESPONSE:
      uint16_t value;
      uint8_t result =
          modbus_process_response(ctx->buffer, ctx->rx_len, &value);

      if (result == MODBUS_ERROR_NONE) {
        if (ctx->on_response) {
          ctx->on_response(ctx->buffer, ctx->rx_len, value);
        }
        ctx->last_value = value;
      } else if (ctx->on_error) {
        ctx->on_error(result);
      }

      ctx->state = MODBUS_IDLE;
      break;
  }
}