"""
Support for particulate matter sensors connected to a serial port.

For more details about this platform, please refer to the documentation at
https://home-assistant.io/components/sensor.serial_pm/
"""
import logging

import voluptuous as vol

from homeassistant.const import CONF_NAME
from homeassistant.helpers.entity import Entity
import homeassistant.helpers.config_validation as cv
from homeassistant.components.sensor import PLATFORM_SCHEMA

REQUIREMENTS = ['pmsensor==0.4']

_LOGGER = logging.getLogger(__name__)

CONF_SERIAL_DEVICE = 'serial_device'
CONF_BRAND = 'brand'

PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
    vol.Required(CONF_BRAND): cv.string,
    vol.Required(CONF_SERIAL_DEVICE): cv.string,
    vol.Optional(CONF_NAME): cv.string,
})


def setup_platform(hass, config, add_entities, discovery_info=None):
    """Set up the available PM sensors."""
    from pmsensor import serial_pm as pm

    try:
        coll = pm.PMDataCollector(
            config.get(CONF_SERIAL_DEVICE),
            pm.SUPPORTED_SENSORS[config.get(CONF_BRAND)]
        )
    except KeyError:
        _LOGGER.error("Brand %s not supported\n supported brands: %s",
                      config.get(CONF_BRAND), pm.SUPPORTED_SENSORS.keys())
        return
    except OSError as err:
        _LOGGER.error("Could not open serial connection to %s (%s)",
                      config.get(CONF_SERIAL_DEVICE), err)
        return

    dev = []

    for pmname in coll.supported_values():
        if config.get(CONF_NAME) is not None:
            name = '{} PM{}'.format(config.get(CONF_NAME), pmname)
        else:
            name = 'PM{}'.format(pmname)
        dev.append(ParticulateMatterSensor(coll, name, pmname))

    add_entities(dev)


class ParticulateMatterSensor(Entity):
    """Representation of an Particulate matter sensor."""

    def __init__(self, pmDataCollector, name, pmname):
        """Initialize a new PM sensor."""
        self._name = name
        self._pmname = pmname
        self._state = None
        self._collector = pmDataCollector

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

    @property
    def state(self):
        """Return the state of the sensor."""
        return self._state

    @property
    def unit_of_measurement(self):
        
    def update(self):
        """Read from sensor and update the state."""
        _LOGGER.debug("Reading data from PM sensor")
        try:
            self._state = self._collector.read_data()[self._pmname]
        except KeyError:
            _LOGGER.error("Could not read PM%s value", self._pmname)

    def should_poll(self):
        """Sensor needs polling."""
        return True

"""Return the unit of measurement of this entity, if any."""
        return "µg/m³"

