"""
homeassistant.components.modbus
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Support for Modbus sensors.

Configuration:

To use the Modbus sensors you will need to add something like the following to
your configuration.yaml file.

sensor:
    platform: modbus
    slave: 1
    registers:
        16:
            name: My integer sensor
            unit: C
        24:
            bits:
                0:
                    name: My boolean sensor
                2:
                    name: My other boolean sensor
    coils:
        0:
            name: My coil switch

Variables:

slave
*Required
Slave number (ignored and can be omitted if not serial Modbus).

unit
*Required
Unit to attach to value (optional, ignored for boolean sensors).

registers
*Required
Contains a list of relevant registers to read from. It can contain a
"bits" section, listing relevant bits.

coils
*Optional
Contains a list of relevant coils to read from.

Note:
- Each named register will create an integer sensor.
- Each named bit will create a boolean sensor.
"""
import logging

import homeassistant.components.modbus as modbus
from homeassistant.helpers.entity import Entity
from homeassistant.const import (
    TEMP_CELCIUS, TEMP_FAHRENHEIT,
    STATE_ON, STATE_OFF)

_LOGGER = logging.getLogger(__name__)
DEPENDENCIES = ['modbus']


def setup_platform(hass, config, add_devices, discovery_info=None):
    """ Read config and create Modbus devices. """
    sensors = []
    slave = config.get("slave", None)
    if modbus.TYPE == "serial" and not slave:
        _LOGGER.error("No slave number provided for serial Modbus")
        return False
    registers = config.get("registers")
    if registers:
        for regnum, register in registers.items():
            if register.get("name"):
                sensors.append(ModbusSensor(register.get("name"),
                                            slave,
                                            regnum,
                                            None,
                                            register.get("unit")))
            if register.get("bits"):
                bits = register.get("bits")
                for bitnum, bit in bits.items():
                    if bit.get("name"):
                        sensors.append(ModbusSensor(bit.get("name"),
                                                    slave,
                                                    regnum,
                                                    bitnum))
    coils = config.get("coils")
    if coils:
        for coilnum, coil in coils.items():
            sensors.append(ModbusSensor(coil.get("name"),
                                        slave,
                                        coilnum,
                                        coil=True))

    add_devices(sensors)


class ModbusSensor(Entity):
    # pylint: disable=too-many-arguments
    """ Represents a Modbus Sensor. """

    def __init__(self, name, slave, register, bit=None, unit=None, coil=False):
        self._name = name
        self.slave = int(slave) if slave else 1
        self.register = int(register)
        self.bit = int(bit) if bit else None
        self._value = None
        self._unit = unit
        self._coil = coil

    def __str__(self):
        return "%s: %s" % (self.name, self.state)

    @property
    def should_poll(self):
        """
        We should poll, because slaves are not allowed to
        initiate communication on Modbus networks.
        """
        return True

    @property
    def unique_id(self):
        """ Returns a unique id. """
        return "MODBUS-SENSOR-{}-{}-{}".format(self.slave,
                                               self.register,
                                               self.bit)

    @property
    def state(self):
        """ Returns the state of the sensor. """
        if self.bit:
            return STATE_ON if self._value else STATE_OFF
        else:
            return self._value

    @property
    def name(self):
        """ Get the name of the sensor. """
        return self._name

    @property
    def unit_of_measurement(self):
        """ Unit of measurement of this entity, if any. """
        if self._unit == "C":
            return TEMP_CELCIUS
        elif self._unit == "F":
            return TEMP_FAHRENHEIT
        else:
            return self._unit

    def update(self):
        """ Update the state of the sensor. """
        if self._coil:
            result = modbus.NETWORK.read_coils(self.register, 1)
            self._value = result.bits[0]
        else:
            result = modbus.NETWORK.read_holding_registers(
                unit=self.slave, address=self.register,
                count=1)
            val = 0
            for i, res in enumerate(result.registers):
                val += res * (2**(i*16))
            if self.bit:
                self._value = val & (0x0001 << self.bit)
            else:
                self._value = val