import datetime as dt
import json
import math
import os
import pytz
import subprocess
import sys
import yaml


def to_iso6801_basic(ts):
    return ts.isoformat().replace(':', '').replace('-', '') \
        .replace('+0000', 'Z')


class Location:

    EARTH_RADIUS_METRES = 6.371e6

    def __init__(self, latitude, longitude, altitude):
        self.latitude = latitude
        self.longitude = longitude
        self.altitude = altitude

    @property
    def latitude_radian(self):
        return math.radians(self.latitude)

    @property
    def longitude_radian(self):
        return math.radians(self.longitude)

    @staticmethod
    def haversine(angle_rad):
        # http://mathworld.wolfram.com/Haversine.html
        return math.sin(angle_rad / 2) ** 2

    @staticmethod
    def haversine_inv(hav):
        # return math.atan2(math.sqrt(hav), math.sqrt(1-hav)) * 2
        return math.asin(math.sqrt(hav)) * 2

    @staticmethod
    def haversine_distance_metres(a, b):
        # https://en.wikipedia.org/wiki/Haversine_formula
        hav = Location.haversine(b.latitude_radian - a.latitude_radian) \
            + math.cos(a.latitude_radian) * math.cos(b.latitude_radian) \
                * Location.haversine(b.longitude_radian - a.longitude_radian)
        return Location.haversine_inv(hav) * Location.EARTH_RADIUS_METRES


class Position(Location):

    def __init__(self, timestamp, latitude, longitude, altitude):
        self.timestamp = timestamp
        super().__init__(
            latitude=latitude,
            longitude=longitude,
            altitude=altitude,
        )

    @classmethod
    def from_termux_location(cls, provider='network'):
        loc_json = subprocess.check_output(['termux-location', '-p', provider]) \
            .decode(sys.stdout.encoding)
        req_ts = dt.datetime.now(pytz.utc)
        loc_attr = yaml.load(loc_json)
        if not loc_attr:
            return None
        else:
            return cls(
                timestamp=req_ts -
                    dt.timedelta(milliseconds=loc_attr['elapsedMs']),
                latitude=loc_attr['latitude'],
                longitude=loc_attr['longitude'],
                altitude=loc_attr['altitude'],
            )

    def save_yaml(self, target_dir_path):
        path = os.path.join(
            target_dir_path,
            '{}.yml'.format(to_iso6801_basic(self.timestamp)),
        )
        attr = {
            'lat': self.latitude,
            'lon': self.longitude,
            'alt': self.altitude,
        }
        with open(path, 'w') as f:
            f.write(yaml.dump(attr, default_flow_style=False))
        return path