from skyfield.api import Topos, load

from .utils import chunks


ISS = "ISS (ZARYA)"
STATIONS_URL = "http://celestrak.com/NORAD/elements/stations.txt"


class Predictions(object):
    def __init__(
        self,
        lat,
        lng,
        altitude=30.0,
        tz="UTC",
        satellite=ISS,
        start=None,
        days=10,
        tle_file=None,
    ):
        self.lat = lat
        self.lng = lng
        self.altitude = altitude
        self.tz = tz
        self.satellite = satellite
        self.start = start
        self.days = days
        self.tle_file = tle_file.resolve().as_posix() if tle_file else STATIONS_URL

    def init_stations(self):
        return load.tle_file(self.tle_file)

    def get_next_days(self):
        ts = load.timescale()
        t0 = ts.now() if not self.start else ts.ut1_jd(self.start)
        t1 = ts.ut1_jd(t0.ut1 + self.days)
        return t0, t1

    def get_location(self):
        return Topos(latitude_degrees=self.lat, longitude_degrees=self.lng)

    def get_satellite(self):
        satellites = self.init_stations()
        by_name = {sat.name: sat for sat in satellites}
        return by_name[self.satellite]

    def get_prediction_details(self, rise, culminate, zet):
        return {"rise": rise, "culminate": culminate, "set": zet}

    def get_prediction_events(self):
        satellite = self.get_satellite()
        t0, t1 = self.get_next_days()
        location = self.get_location()

        ts, _events = satellite.find_events(
            location, t0, t1, altitude_degrees=self.altitude
        )

        # events are returned as 3-tuples of (rise, culminate, set)
        # where rise/set are relative to given altitude
        # docs mention the possibilibity of several culminations
        # https://rhodesmill.org/skyfield/earth-satellites.html#finding-when-a-satellite-rises-and-sets
        # but this doesn't seem to happen in our case
        return list(chunks(ts, 3))

    def get_predictions(self):
        preds = self.get_prediction_events()
        return [self.get_prediction_details(*p) for p in preds]