"""
.. moduleauthor:: Fabio Manganiello <blacklight86@gmail.com>
.. license: MIT
"""

import logging
import re
import socket
import time

from threading import Thread, Event as ThreadEvent, get_ident
from typing import Optional, Dict

from platypush.bus import Bus
from platypush.common import ExtensionWithManifest
from platypush.config import Config
from platypush.context import get_backend
from platypush.message.event.zeroconf import ZeroconfServiceAddedEvent, ZeroconfServiceRemovedEvent
from platypush.utils import set_timeout, clear_timeout, \
    get_redis_queue_name_by_message, set_thread_name, get_backend_name_by_class

from platypush import __version__
from platypush.event import EventGenerator
from platypush.message import Message
from platypush.message.event import Event
from platypush.message.request import Request
from platypush.message.response import Response


class Backend(Thread, EventGenerator, ExtensionWithManifest):
    """
    Parent class for backends.

    A backend is basically a thread that checks for new events on some channel
    (e.g. a network socket, a queue, some new entries on an API endpoint or an
    RSS feed, a voice command through an assistant, a new measure from a sensor
    etc.) and propagates event messages to the main application bus whenever a
    new event happens. You can then build whichever type of custom logic you
    want on such events.
    """

    _default_response_timeout = 5

    # Loop function, can be implemented by derived classes
    loop = None

    def __init__(self, bus: Optional[Bus] = None, poll_seconds: Optional[float] = None, **kwargs):
        """
        :param bus: Reference to the bus object to be used in the backend
        :param poll_seconds: If the backend implements a ``loop`` method, this parameter expresses how often the
            loop should run in seconds.
        :param kwargs: Key-value configuration for the backend
        """

        self._thread_name = self.__class__.__name__
        EventGenerator.__init__(self)
        ExtensionWithManifest.__init__(self)
        Thread.__init__(self, name=self._thread_name, daemon=True)

        # If no bus is specified, create an internal queue where
        # the received messages will be pushed
        self.bus = bus or Bus()
        self.poll_seconds = float(poll_seconds) if poll_seconds else None
        self.device_id = Config.get('device_id')
        self.thread_id = None
        self._stop_event = ThreadEvent()
        self._kwargs = kwargs
        self.logger = logging.getLogger('platypush:backend:' + get_backend_name_by_class(self.__class__))
        self.zeroconf = None
        self.zeroconf_info = None

        # Internal-only, we set the request context on a backend if that
        # backend is intended to react for a response to a specific request
        self._request_context = kwargs['_req_ctx'] if '_req_ctx' in kwargs \
            else None

        if 'logging' in kwargs:
            self.logger.setLevel(getattr(logging, kwargs.get('logging').upper()))

    def on_message(self, msg):
        """
        Callback when a message is received on the backend.
        It parses and posts the message on the main bus.
        It should be called by the derived classes whenever
        a new message should be processed.

        :param msg: Received message.  It can be either a key-value dictionary, a platypush.message.Message object,
            or a string/byte UTF-8 encoded string
        """

        msg = Message.build(msg)

        if not getattr(msg, 'target') or msg.target != self.device_id:
            return  # Not for me

        self.logger.debug('Message received on the {} backend: {}'.format(
            self.__class__.__name__, msg))

        if self._is_expected_response(msg):
            # Expected response, trigger the response handler
            clear_timeout()
            self._request_context['on_response'](msg)
            self.stop()
            return

        msg.backend = self   # Augment message to be able to process responses
        self.bus.post(msg)

    def _is_expected_response(self, msg):
        """ Internal only - returns true if we are expecting for a response
            and msg is that response """

        return self._request_context \
            and isinstance(msg, Response) \
            and msg.id == self._request_context['request'].id

    def _get_backend_config(self):
        config_name = 'backend.' + self.__class__.__name__.split('Backend')[0].lower()
        return Config.get(config_name)

    def _setup_response_handler(self, request, on_response, response_timeout):
        def _timeout_hndl():
            raise RuntimeError('Timed out while waiting for a response from {}'.
                               format(request.target))

        req_ctx = {
            'request': request,
            'on_response': on_response,
            'response_timeout': response_timeout,
        }

        resp_backend = self.__class__(bus=self.bus, _req_ctx=req_ctx,
                                      **self._get_backend_config(), **self._kwargs)

        # Set the response timeout
        if response_timeout:
            set_timeout(seconds=response_timeout, on_timeout=_timeout_hndl)

        resp_backend.start()

    def send_event(self, event, **kwargs):
        """
        Send an event message on the backend.

        :param event: Event to send. It can be a dict, a string/bytes UTF-8 JSON, or a platypush.message.event.Event
            object.
        """

        event = Event.build(event)
        assert isinstance(event, Event)

        event.origin = self.device_id
        if not hasattr(event, 'target'):
            event.target = self.device_id

        self.send_message(event, **kwargs)

    def send_request(self, request, on_response=None,
                     response_timeout=_default_response_timeout, **kwargs):
        """
        Send a request message on the backend.

        :param request: The request, either a dict, a string/bytes UTF-8 JSON, or a platypush.message.request.Request
            object.

        :param on_response: Optional callback that will be called when a response is received. If set, this method will
            synchronously wait for a response before exiting.
        :type on_response: function

        :param response_timeout: If on_response is set, the backend will raise an exception if the response isn't
            received within this number of seconds (default: None)
        :type response_timeout: float
        """

        request = Request.build(request)
        assert isinstance(request, Request)

        request.origin = self.device_id

        if on_response and response_timeout != 0:
            self._setup_response_handler(request, on_response, response_timeout)

        self.send_message(request, **kwargs)

    def send_response(self, response, request, **kwargs):
        """
        Send a response message on the backend.

        :param response: The response, either a dict, a string/bytes UTF-8 JSON, or a
            :class:`platypush.message.response.Response` object.
        :param request: Associated request, used to set the response parameters that will link them
        """

        assert isinstance(response, Response)
        assert isinstance(request, Request)

        self.send_message(response, **kwargs)

    def send_message(self, msg, queue_name=None, **kwargs):
        """
        Sends a platypush.message.Message to a node.
        To be implemented in the derived classes. By default, if the Redis
        backend is configured then it will try to deliver the message to
        other consumers through the configured Redis main queue.

        :param msg: The message to send
        :param queue_name: Send the message on a specific queue (default: the queue_name configured on the Redis
            backend)
        """

        try:
            redis = get_backend('redis')
            if not redis:
                raise KeyError()
        except KeyError:
            self.logger.warning("Backend {} does not implement send_message " +
                                "and the fallback Redis backend isn't configured")
            return

        redis.send_message(msg, queue_name=queue_name)

    def run(self):
        """ Starts the backend thread. To be implemented in the derived classes if the loop method isn't defined. """
        self.thread_id = get_ident()
        set_thread_name(self._thread_name)
        if not callable(self.loop):
            return

        while not self.should_stop():
            try:
                with self:
                    has_error = False

                    while not self.should_stop() and not has_error:
                        try:
                            self.loop()
                        except Exception as e:
                            has_error = True
                            self.logger.error(str(e))
                            self.logger.exception(e)
                        finally:
                            if self.poll_seconds:
                                time.sleep(self.poll_seconds)
                            elif has_error:
                                time.sleep(5)
            except Exception as e:
                self.logger.error('{} initialization error: {}'.format(self.__class__.__name__, str(e)))
                self.logger.exception(e)
                time.sleep(self.poll_seconds or 5)

    def __enter__(self):
        """ Invoked when the backend is initialized, if the main logic is within a ``loop()`` function """
        self.logger.info('Initialized backend {}'.format(self.__class__.__name__))

    def __exit__(self, exc_type, exc_val, exc_tb):
        """ Invoked when the backend is terminated, if the main logic is within a ``loop()`` function """
        self.on_stop()
        self.logger.info('Terminated backend {}'.format(self.__class__.__name__))

    def on_stop(self):
        """ Callback invoked when the process stops """
        pass

    def stop(self):
        """ Stops the backend thread by sending a STOP event on its bus """
        def _async_stop():
            self._stop_event.set()
            self.unregister_service()
            self.on_stop()

        Thread(target=_async_stop).start()

    def should_stop(self):
        return self._stop_event.is_set()

    def wait_stop(self, timeout=None) -> bool:
        return self._stop_event.wait(timeout)

    def _get_redis(self):
        import redis

        redis_backend = get_backend('redis')
        if not redis_backend:
            self.logger.warning('Redis backend not configured - some ' +
                                'web server features may not be working properly')
            redis_args = {}
        else:
            redis_args = redis_backend.redis_args

        redis = redis.Redis(**redis_args)
        return redis

    def get_message_response(self, msg):
        try:
            redis = self._get_redis()
            response = redis.blpop(get_redis_queue_name_by_message(msg), timeout=60)
            if response and len(response) > 1:
                response = Message.build(response[1])
            else:
                response = None

            return response
        except Exception as e:
            self.logger.error('Error while processing response to {}: {}'.format(msg, str(e)))

    @staticmethod
    def _get_ip() -> str:
        """
        Get the IP address of the machine.
        """
        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        s.connect(('8.8.8.8', 80))
        addr = s.getsockname()[0]
        s.close()
        return addr

    def register_service(self,
                         port: Optional[int] = None,
                         name: Optional[str] = None,
                         srv_type: Optional[str] = None,
                         srv_name: Optional[str] = None,
                         udp: bool = False,
                         properties: Optional[Dict] = None):
        """
        Initialize the Zeroconf service configuration for this backend.

        :param port: Service listen port (default: the backend ``port`` attribute if available, or ``None``).
        :param name: Service short name (default: backend name).
        :param srv_type: Service type (default: ``_platypush-{name}._{proto}.local.``).
        :param srv_name: Full service name (default: ``{hostname or device_id}.{type}``).
        :param udp: Set to True if this is a UDP service.
        :param properties: Extra properties to be passed on the service. Default:

            .. code-block:: json

                {
                    "name": "Platypush",
                    "vendor": "Platypush",
                    "version": "{platypush_version}"
                }

        """
        try:
            from zeroconf import ServiceInfo, Zeroconf
            from platypush.plugins.zeroconf import ZeroconfListener
        except ImportError:
            self.logger.warning('zeroconf package not available, service discovery will be disabled.')
            return

        self.zeroconf = Zeroconf()
        srv_desc = {
            'name': 'Platypush',
            'vendor': 'Platypush',
            'version': __version__,
            **(properties or {}),
        }

        name = name or re.sub(r'Backend$', '', self.__class__.__name__).lower()
        srv_type = srv_type or '_platypush-{name}._{proto}.local.'.format(name=name, proto='udp' if udp else 'tcp')
        srv_name = srv_name or '{host}.{type}'.format(host=self.device_id, type=srv_type)

        if port:
            srv_port = port
        else:
            srv_port = self.port if hasattr(self, 'port') else None

        self.zeroconf_info = ServiceInfo(srv_type, srv_name,
                                         addresses=[socket.inet_aton(self._get_ip())],
                                         port=srv_port,
                                         weight=0,
                                         priority=0,
                                         properties=srv_desc)

        if not self.zeroconf_info:
            self.logger.warning('Could not register Zeroconf service')
            return

        self.zeroconf.register_service(self.zeroconf_info)
        self.bus.post(ZeroconfServiceAddedEvent(service_type=srv_type, service_name=srv_name,
                                                service_info=ZeroconfListener.parse_service_info(self.zeroconf_info)))

    def unregister_service(self):
        """
        Unregister the Zeroconf service configuration if available.
        """
        if self.zeroconf and self.zeroconf_info:
            try:
                self.zeroconf.unregister_service(self.zeroconf_info)
            except Exception as e:
                self.logger.warning('Could not register Zeroconf service {}: {}: {}'.format(
                    self.zeroconf_info.name, type(e).__name__, str(e)))

            if self.zeroconf:
                self.zeroconf.close()

            if self.zeroconf_info:
                self.bus.post(ZeroconfServiceRemovedEvent(service_type=self.zeroconf_info.type,
                                                          service_name=self.zeroconf_info.name))
            else:
                self.bus.post(ZeroconfServiceRemovedEvent(service_type=None, service_name=None))

            self.zeroconf_info = None
            self.zeroconf = None


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