from datetime import datetime

import pytz

from core.constants import SOFTWARE_NAME, SOFTWARE_VERSION


# Generic data provider class. Subclasses of this query the individual APIs for data.
class Provider:

    # HTTP headers used for providers that use HTTP
    HTTP_HEADERS = { "User-Agent": SOFTWARE_NAME + " " + SOFTWARE_VERSION }

    # Constructor
    def __init__(self):
        self.last_update_time = datetime.min.replace(tzinfo=pytz.UTC)
        self.last_spot_time = datetime.min.replace(tzinfo=pytz.UTC)
        self.status = "Not Started"
        self.spot_list = None

    # Return the name of the provider
    def name(self):
        raise NotImplementedError("Subclasses must implement this method")

    # Set up the provider, e.g. giving it the spot list to work from
    def setup(self, spot_list):
        self.spot_list = spot_list

    # Start the provider. This should return immediately after spawning threads to access the remote resources
    def start(self):
        raise NotImplementedError("Subclasses must implement this method")

    # Submit one or more new spots retrieved from the provider. Only spots that are newer than the last spot retrieved
    # by this provider will be added to the spot list, to prevent duplications. This is called by the subclasses on
    # receiving spots.
    def submit(self, spots):
        for spot in spots:
            if spot.time > self.last_spot_time:
                self.spot_list.append(spot)
        self.last_spot_time = max(map(lambda s: s.time, spots))

    # Stop any threads and prepare for application shutdown
    def stop(self):
        raise NotImplementedError("Subclasses must implement this method")