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]
    input_registers = {
            'T': 30010,    # from SHT4x
            'T_F': 30011,
            'RH': 30012,   # from SHT4x
            'CO2': 30013,  # from SCD4x
            'VOC_index': 30014,
            'VOC_ticks': 30015,
            'NOx_index': 30016,
            'NOx_ticks': 30017,
            'PM_mass_concentration_1.0': 30018,
            'PM_mass_concentration_2.5': 30019,
            'PM_mass_concentration_4.0': 30020,
            'PM_mass_concentration_10.0': 30021,
            'PM_number_concentration_0.5': 30022,
            'PM_number_concentration_1.0': 30023,
            'PM_number_concentration_2.5': 30024,
            'PM_number_concentration_4.0': 30025,
            'PM_number_concentration_10.0': 30026,
            'PM_typical_particle_size':  30027,
            'T_SCD4x': 30028,
            'T_SCF4x_F': 30029,
            'RH_SCD4x': 30030}
    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}
    reset_register = 40100
    reset_magic_number = 0xABCD
    # 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

    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

    def reset(self):
        try:
            self.write_register(self.reset_register, self.reset_magic_number)
            return False # got answer => failed to reset
        except minimalmodbus.NoResponseError:
            return True # no answer => reset successful


    @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'])

    def read_register(self, register_number, signed=False, 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, signed=signed) * 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 

    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