"""
Support for monitoring if a sensor value is below/above a threshold.

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

import voluptuous as vol

import homeassistant.helpers.config_validation as cv
from homeassistant.components.binary_sensor import (
    BinarySensorDevice, PLATFORM_SCHEMA, DEVICE_CLASSES_SCHEMA)
from homeassistant.const import (
    CONF_NAME, CONF_ENTITY_ID, CONF_TYPE, STATE_UNKNOWN,
    ATTR_ENTITY_ID, CONF_DEVICE_CLASS)
from homeassistant.core import callback
from homeassistant.helpers.event import async_track_state_change

_LOGGER = logging.getLogger(__name__)

ATTR_SENSOR_VALUE = 'sensor_value'
ATTR_THRESHOLD = 'threshold'
ATTR_TYPE = 'type'

CONF_LOWER = 'lower'
CONF_THRESHOLD = 'threshold'
CONF_UPPER = 'upper'

DEFAULT_NAME = 'Threshold'

SENSOR_TYPES = [CONF_LOWER, CONF_UPPER]

PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
    vol.Required(CONF_ENTITY_ID): cv.entity_id,
    vol.Required(CONF_THRESHOLD): vol.Coerce(float),
    vol.Required(CONF_TYPE): vol.In(SENSOR_TYPES),
    vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string,
    vol.Optional(CONF_DEVICE_CLASS): DEVICE_CLASSES_SCHEMA,
})


@asyncio.coroutine
def async_setup_platform(hass, config, async_add_devices, discovery_info=None):
    """Set up the Threshold sensor."""
    entity_id = config.get(CONF_ENTITY_ID)
    name = config.get(CONF_NAME)
    threshold = config.get(CONF_THRESHOLD)
    limit_type = config.get(CONF_TYPE)
    device_class = config.get(CONF_DEVICE_CLASS)

    async_add_devices(
        [ThresholdSensor(hass, entity_id, name, threshold, limit_type,
                         device_class)], True)
    return True


class ThresholdSensor(BinarySensorDevice):
    """Representation of a Threshold sensor."""

    def __init__(self, hass, entity_id, name, threshold, limit_type,
                 device_class):
        """Initialize the Threshold sensor."""
        self._hass = hass
        self._entity_id = entity_id
        self.is_upper = limit_type == 'upper'
        self._name = name
        self._threshold = threshold
        self._device_class = device_class
        self._deviation = False
        self.sensor_value = 0

        @callback
        # pylint: disable=invalid-name
        def async_threshold_sensor_state_listener(
                entity, old_state, new_state):
            """Handle sensor state changes."""
            if new_state.state == STATE_UNKNOWN:
                return

            try:
                self.sensor_value = float(new_state.state)
            except ValueError:
                _LOGGER.error("State is not numerical")

            hass.async_add_job(self.async_update_ha_state, True)

        async_track_state_change(
            hass, entity_id, async_threshold_sensor_state_listener)

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

    @property
    def is_on(self):
        """Return true if sensor is on."""
        return self._deviation

    @property
    def should_poll(self):
        """No polling needed."""
        return False

    @property
    def device_class(self):
        """Return the sensor class of the sensor."""
        return self._device_class

    @property
    def device_state_attributes(self):
        """Return the state attributes of the sensor."""
        return {
            ATTR_ENTITY_ID: self._entity_id,
            ATTR_SENSOR_VALUE: self.sensor_value,
            ATTR_THRESHOLD: self._threshold,
            ATTR_TYPE: CONF_UPPER if self.is_upper else CONF_LOWER,
        }

    @asyncio.coroutine
    def async_update(self):
        """Get the latest data and updates the states."""
        if self.is_upper:
            self._deviation = bool(self.sensor_value > self._threshold)
        else:
            self._deviation = bool(self.sensor_value < self._threshold)