import logging
from datetime import datetime
from threading import Timer, Thread
from time import sleep

import pytz
import requests

from alertproviders.alert_provider import AlertProvider
from core.constants import HTTP_HEADERS


# Generic alert provider class for providers that request data via HTTP(S). Just for convenience to avoid code
# duplication. Subclasses of this query the individual APIs for data.
class HTTPAlertProvider(AlertProvider):

    def __init__(self, provider_config, url, poll_interval):
        super().__init__(provider_config)
        self.url = url
        self.poll_interval = poll_interval
        self.poll_timer = None

    def start(self):
        # Fire off a one-shot thread to run poll() for the first time, just to ensure start() returns immediately and
        # the application can continue starting. The thread itself will then die, and the timer will kick in on its own
        # thread.
        logging.info("Set up query of " + self.name + " alert API every " + str(self.poll_interval) + " seconds.")
        thread = Thread(target=self.poll)
        thread.daemon = True
        thread.start()

    def stop(self):
        self.poll_timer.cancel()

    def poll(self):
        try:
            # Request data from API
            logging.debug("Polling " + self.name + " alert API...")
            http_response = requests.get(self.url, headers=HTTP_HEADERS)
            # Pass off to the subclass for processing
            new_alerts = self.http_response_to_alerts(http_response)
            # Submit the new alerts for processing. There might not be any alerts for the less popular programs.
            if new_alerts:
                self.submit_batch(new_alerts)

            self.status = "OK"
            self.last_update_time = datetime.now(pytz.UTC)
            logging.debug("Received data from " + self.name + " alert API.")

        except Exception as e:
            self.status = "Error"
            logging.exception("Exception in HTTP JSON Alert Provider (" + self.name + ")")
            sleep(1)

        self.poll_timer = Timer(self.poll_interval, self.poll)
        self.poll_timer.start()

    # Convert an HTTP response returned by the API into alert data. The whole response is provided here so the subclass
    # implementations can check for HTTP status codes if necessary, and handle the response as JSON, XML, text, whatever
    # the API actually provides.
    def http_response_to_alerts(self, http_response):
        raise NotImplementedError("Subclasses must implement this method")