import minimalmodbus
import serial
import time

class Sensor():
    # MODBUS constants
    holding_register_start = 40001
    holding_register_end = 49999
    input_register_start = 30001
    input_register_end = 39999
    # Sensor specific config
    baudrates = [ 4800,9600,14400,19200,28800,38400,57600,76800,115200 ] # allowed baudrates
    input_registers = { \
            'CO2': 30010, \
            'T_SHT4x': 30011, \
            'RH_SHT4x': 30012, \
            'T_SCD4x': 30013, \
            'RH_SCD4x': 30014, \
            'T_SHT4x_signed': 30015, \
            'T_SCD4x_signed': 30016 }
    holding_registers = { \
            'LED_on': 40001, \
            'LED_brightness': 40002, \
            'LED_smooth': 40003, \
            'CO2_alert_limit_1': 40004, \
            'CO2_alert_limit_2': 40005, \
            'SCD4x_temperature_offset': 40006, \
            'MODBUS_address': 40007, \
            'baudrate': 40008 }
    # readout and error counters
    readout_total = 0
    readout_error_invalid_response = 0 # checksum error: bus transmission corrupted?
    readout_error_no_response = 0 # no response - sensor device was busy
    # methods
    def __init__(self, address=247, baudrate=19200, dev_file='/dev/rs485'):
        self.dev_file = dev_file
        self.address = address
        self.baudrate = baudrate
        self.open()
    def open(self):
        self.serial = minimalmodbus.Instrument(self.dev_file, self.address, close_port_after_each_call=True)
        self.serial.serial.baudrate = self.baudrate
        self.serial.serial.bytesize = 8
        self.serial.serial.parity   = serial.PARITY_EVEN
        self.serial.serial.stopbits = 1
        self.serial.serial.timeout  = 0.05          # seconds
        self.serial.mode = minimalmodbus.MODE_RTU   # rtu or ascii mode
        self.serial.clear_buffers_before_each_transaction = True
    def close(self):
        self.serial.serial.close()
        self.serial = None
    # High level read functions
    @property
    def CO2(self):
        return int(self.read_register(self.input_registers['CO2']))
    @property
    def T(self):
        # TODO maybe use rather signed version?
        return self.T_SHT4x
    @property
    def RH(self):
        return self.RH_SHT4x
    @property
    def T_SHT4x(self):
        return self.read_register(self.input_registers['T_SHT4x']) / 10
    @property
    def T_SHT4x_signed(self):
        return self.read_register(self.input_registers['T_SHT4x_signed'], signed=True) / 10
    @property
    def RH_SHT4x(self):
        return self.read_register(self.input_registers['RH_SHT4x'])
    @property
    def T_SCD4x(self):
        return self.read_register(self.input_registers['T_SCD4x']) / 10
    @property
    def T_SCD4x_signed(self):
        return self.read_register(self.input_register['T_SCD4x_signed'], signed=True) / 10
    @property
    def RH_SCD4x(self):
        return self.read_register(self.input_registers['RH_SCD4x'])
    # generic read register function
    def read_register(self, register_number, retries=10):
        if self.input_register_start <= register_number <= self.input_register_end:
            function_code = 4
            register_offset = register_number - self.input_register_start
        elif self.holding_register_start <= register_number <= self.holding_register_end:
            function_code = 3
            register_offset = register_number - self.holding_register_start
        else:
            # wrong register number
            raise ValueError
        while retries:
            retries -= 1
            try:
                self.readout_total += 1
                # minimalmodbus divides received register value by 10
                return self.serial.read_register(register_offset, 1, functioncode=function_code) * 10
            except minimalmodbus.NoResponseError as e:
                last_exception = e
                self.readout_error_no_response += 1
                continue
            except minimalmodbus.InvalidResponseError as e:
                last_exception = e
                self.readout_error_invalid_response += 1
                continue
        # retries failed, raise last exception to inform user
        raise last_exception 
    # generic write register function
    def write_register(self, register_number, register_value, retries=10):
        if not self.holding_register_start <= register_number <= self.holding_register_end:
            raise ValueError
        register_offset = register_number - self.holding_register_start
        while retries:
            retries -= 1
            try:
                return self.serial.write_register(register_offset, register_value, functioncode=6)
            except (minimalmodbus.NoResponseError, minimalmodbus.InvalidResponseError) as e:
                last_exception = e
                continue
        raise last_exception