Luftdaten sensor (#10274)

* Add sensor platform for luftdaten.info

* Add monitored conditions to platform schema

* Make monitored conditions config obligatory

* Improve inline documentation

* Import first standard libs then 3rd party libs

* Combine resource url using format

* Remove unnecessary try..except block

* Use state “None” instead of STATE_UNKNOWN

* Minor changes incl. removal of unused vars

* Add missing spaces

.coveragerc

@@ -520,6 +520,7 @@ omit =
     homeassistant/components/sensor/lastfm.py
     homeassistant/components/sensor/linux_battery.py
     homeassistant/components/sensor/loopenergy.py
+    homeassistant/components/sensor/luftdaten.py
     homeassistant/components/sensor/lyft.py
     homeassistant/components/sensor/metoffice.py
     homeassistant/components/sensor/miflora.py

homeassistant/components/sensor/luftdaten.py

@@ -0,0 +1,142 @@
+"""
+Support for Luftdaten sensors.
+
+For more details about this platform, please refer to the documentation at
+https://home-assistant.io/components/sensor.luftdaten/
+"""
+import asyncio
+import json
+import logging
+from datetime import timedelta
+
+import requests
+import voluptuous as vol
+
+from homeassistant.components.sensor import PLATFORM_SCHEMA
+from homeassistant.const import (
+    CONF_NAME, CONF_RESOURCE, CONF_VERIFY_SSL, CONF_MONITORED_CONDITIONS,
+    TEMP_CELSIUS)
+from homeassistant.helpers.entity import Entity
+import homeassistant.helpers.config_validation as cv
+
+_LOGGER = logging.getLogger(__name__)
+
+VOLUME_MICROGRAMS_PER_CUBIC_METER = 'µg/m3'
+
+SENSOR_TEMPERATURE = 'temperature'
+SENSOR_HUMIDITY = 'humidity'
+SENSOR_PM10 = 'P1'
+SENSOR_PM2_5 = 'P2'
+
+SENSOR_TYPES = {
+    SENSOR_TEMPERATURE: ['Temperature', TEMP_CELSIUS],
+    SENSOR_HUMIDITY: ['Humidity', '%'],
+    SENSOR_PM10: ['PM10', VOLUME_MICROGRAMS_PER_CUBIC_METER],
+    SENSOR_PM2_5: ['PM2.5', VOLUME_MICROGRAMS_PER_CUBIC_METER]
+}
+
+DEFAULT_NAME = 'Luftdaten Sensor'
+DEFAULT_RESOURCE = 'https://api.luftdaten.info/v1/sensor/'
+DEFAULT_VERIFY_SSL = True
+
+CONF_SENSORID = 'sensorid'
+
+SCAN_INTERVAL = timedelta(minutes=3)
+
+PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
+    vol.Required(CONF_SENSORID): cv.positive_int,
+    vol.Required(CONF_MONITORED_CONDITIONS):
+        vol.All(cv.ensure_list, [vol.In(SENSOR_TYPES)]),
+    vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string,
+    vol.Optional(CONF_RESOURCE, default=DEFAULT_RESOURCE): cv.string,
+    vol.Optional(CONF_VERIFY_SSL, default=DEFAULT_VERIFY_SSL): cv.boolean
+})
+
+
+@asyncio.coroutine
+def async_setup_platform(hass, config, async_add_devices, discovery_info=None):
+    """Set up the Luftdaten sensor."""
+    name = config.get(CONF_NAME)
+    sensorid = config.get(CONF_SENSORID)
+    verify_ssl = config.get(CONF_VERIFY_SSL)
+
+    resource = '{}{}/'.format(config.get(CONF_RESOURCE), sensorid)
+
+    rest_client = LuftdatenData(resource, verify_ssl)
+    rest_client.update()
+
+    if rest_client.data is None:
+        _LOGGER.error("Unable to fetch Luftdaten data")
+        return False
+
+    devices = []
+    for variable in config[CONF_MONITORED_CONDITIONS]:
+        devices.append(LuftdatenSensor(rest_client, name, variable))
+
+    async_add_devices(devices, True)
+
+
+class LuftdatenSensor(Entity):
+    """Implementation of a LuftdatenSensor sensor."""
+
+    def __init__(self, rest_client, name, sensor_type):
+        """Initialize the LuftdatenSensor sensor."""
+        self.rest_client = rest_client
+        self._name = name
+        self._state = None
+        self.sensor_type = sensor_type
+        self._unit_of_measurement = SENSOR_TYPES[sensor_type][1]
+
+    @property
+    def name(self):
+        """Return the name of the sensor."""
+        return '{} {}'.format(self._name, SENSOR_TYPES[self.sensor_type][0])
+
+    @property
+    def state(self):
+        """Return the state of the device."""
+        return self._state
+
+    @property
+    def unit_of_measurement(self):
+        """Return the unit of measurement of this entity, if any."""
+        return self._unit_of_measurement
+
+    def update(self):
+        """Get the latest data from REST API and update the state."""
+        self.rest_client.update()
+        value = self.rest_client.data
+
+        if value is None:
+            self._state = None
+        else:
+            parsed_json = json.loads(value)
+
+            log_entries_count = len(parsed_json) - 1
+            latest_log_entry = parsed_json[log_entries_count]
+            sensordata_values = latest_log_entry['sensordatavalues']
+            for sensordata_value in sensordata_values:
+                if sensordata_value['value_type'] == self.sensor_type:
+                    self._state = sensordata_value['value']
+
+
+class LuftdatenData(object):
+    """Class for handling the data retrieval."""
+
+    def __init__(self, resource, verify_ssl):
+        """Initialize the data object."""
+        self._request = requests.Request('GET', resource).prepare()
+        self._verify_ssl = verify_ssl
+        self.data = None
+
+    def update(self):
+        """Get the latest data from Luftdaten service."""
+        try:
+            with requests.Session() as sess:
+                response = sess.send(
+                    self._request, timeout=10, verify=self._verify_ssl)
+
+            self.data = response.text
+        except requests.exceptions.RequestException:
+            _LOGGER.error("Error fetching data: %s", self._request)
+            self.data = None