Netdata sensor (#4743)

* Added netdata sensor

* Typo

* Add netdata sensor

* Improvement of the work done by @ezar

.coveragerc

@@ -281,6 +281,7 @@ omit =
     homeassistant/components/sensor/mhz19.py
     homeassistant/components/sensor/miflora.py
     homeassistant/components/sensor/mqtt_room.py
+    homeassistant/components/sensor/netdata.py
     homeassistant/components/sensor/neurio_energy.py
     homeassistant/components/sensor/nut.py
     homeassistant/components/sensor/nzbget.py

homeassistant/components/sensor/netdata.py

+"""
+Support gathering system information of hosts which are running netdata.
+
+For more details about this platform, please refer to the documentation at
+https://home-assistant.io/components/sensor.netdata/
+"""
+import logging
+from datetime import timedelta
+
+import requests
+import voluptuous as vol
+
+import homeassistant.helpers.config_validation as cv
+from homeassistant.components.sensor import PLATFORM_SCHEMA
+from homeassistant.const import (
+    CONF_HOST, CONF_PORT, STATE_UNKNOWN, CONF_NAME, CONF_RESOURCES)
+from homeassistant.helpers.entity import Entity
+from homeassistant.util import Throttle
+
+_LOGGER = logging.getLogger(__name__)
+_RESOURCE = 'api/v1'
+_REALTIME = 'before=0&after=-1&options=seconds'
+
+DEFAULT_HOST = 'localhost'
+DEFAULT_NAME = 'Netdata'
+DEFAULT_PORT = '19999'
+
+MIN_TIME_BETWEEN_UPDATES = timedelta(seconds=60)
+
+SENSOR_TYPES = {
+    'memory_free': ['RAM Free', 'MiB', 'system.ram', 'free', 1],
+    'memory_used': ['RAM Used', 'MiB', 'system.ram', 'used', 1],
+    'memory_cached': ['RAM Cached', 'MiB', 'system.ram', 'cached', 1],
+    'memory_buffers': ['RAM Buffers', 'MiB', 'system.ram', 'buffers', 1],
+    'swap_free': ['Swap Free', 'MiB', 'system.swap', 'free', 1],
+    'swap_used': ['Swap Used', 'MiB', 'system.swap', 'used', 1],
+    'processes_running': ['Processes Running', 'Count', 'system.processes',
+                          'running', 0],
+    'processes_blocked': ['Processes Blocked', 'Count', 'system.processes',
+                          'blocked', 0],
+    'system_load': ['System Load', '15 min', 'system.processes', 'running', 2],
+    'system_io_in': ['System IO In', 'Count', 'system.io', 'in', 0],
+    'system_io_out': ['System IO Out', 'Count', 'system.io', 'out', 0],
+}
+
+PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
+    vol.Optional(CONF_HOST, default=DEFAULT_HOST): cv.string,
+    vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string,
+    vol.Optional(CONF_PORT, default=DEFAULT_PORT): cv.port,
+    vol.Optional(CONF_RESOURCES, default=['memory_free']):
+        vol.All(cv.ensure_list, [vol.In(SENSOR_TYPES)]),
+})
+
+
+# pylint: disable=unused-variable
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    """Set up the Netdata sensor."""
+    name = config.get(CONF_NAME)
+    host = config.get(CONF_HOST)
+    port = config.get(CONF_PORT)
+    url = 'http://{}:{}'.format(host, port)
+    version_url = '{}/version.txt'.format(url)
+    data_url = '{}/{}/data?chart='.format(url, _RESOURCE)
+    resources = config.get(CONF_RESOURCES)
+
+    try:
+        response = requests.get(version_url, timeout=10)
+        if not response.ok:
+            _LOGGER.error("Response status is '%s'", response.status_code)
+            return False
+    except requests.exceptions.ConnectionError:
+        _LOGGER.error("No route to resource/endpoint: %s", url)
+        return False
+
+    values = {}
+    for key, value in sorted(SENSOR_TYPES.items()):
+        if key in resources:
+            values.setdefault(value[2], []).append(key)
+
+    dev = []
+    for chart in values:
+        rest_url = '{}{}&{}'.format(data_url, chart, _REALTIME)
+        rest = NetdataData(rest_url)
+        for sensor_type in values[chart]:
+            dev.append(NetdataSensor(rest, name, sensor_type))
+
+    add_devices(dev)
+
+
+class NetdataSensor(Entity):
+    """Implementation of a Netdata sensor."""
+
+    def __init__(self, rest, name, sensor_type):
+        """Initialize the sensor."""
+        self.rest = rest
+        self.type = sensor_type
+        self._name = '{} {}'.format(name, SENSOR_TYPES[self.type][0])
+        self._precision = SENSOR_TYPES[self.type][4]
+        self._unit_of_measurement = SENSOR_TYPES[self.type][1]
+        self.update()
+
+    @property
+    def name(self):
+        """The name of the sensor."""
+        return self._name
+
+    @property
+    def unit_of_measurement(self):
+        """Return the unit the value is expressed in."""
+        return self._unit_of_measurement
+
+    @property
+    def state(self):
+        """Return the state of the resources."""
+        value = self.rest.data
+
+        if value is not None:
+            netdata_id = SENSOR_TYPES[self.type][3]
+            if netdata_id in value:
+                return "{0:.{1}f}".format(value[netdata_id], self._precision)
+            else:
+                return STATE_UNKNOWN
+
+    def update(self):
+        """Get the latest data from Netdata REST API."""
+        self.rest.update()
+
+
+class NetdataData(object):
+    """The class for handling the data retrieval."""
+
+    def __init__(self, resource):
+        """Initialize the data object."""
+        self._resource = resource
+        self.data = None
+
+    @Throttle(MIN_TIME_BETWEEN_UPDATES)
+    def update(self):
+        """Get the latest data from the Netdata REST API."""
+        try:
+            response = requests.get(self._resource, timeout=5)
+            det = response.json()
+            self.data = {k: v for k, v in zip(det['labels'], det['data'][0])}
+
+        except requests.exceptions.ConnectionError:
+            _LOGGER.error("No route to host/endpoint: %s", self._resource)
+            self.data = None