from math import radians

from django.db.models import F, Value
from django.db.models.functions import Radians, Sin, ATan2, Sqrt, Cos


def calculate_distance(qs, client_lat: float, client_lon: float):
    """
        Based on stackoverflow question: https://stackoverflow.com/a/19412565/10261581
        Distance Unit is in Kilometres

        R = 6373.0

        lat1 = radians(52.2296756)
        lon1 = radians(21.0122287)
        lat2 = radians(52.406374)
        lon2 = radians(16.9251681)

        dlon = lon2 - lon1
        dlat = lat2 - lat1

        a = sin(dlat / 2)**2 + cos(lat1) * cos(lat2) * sin(dlon / 2)**2
        c = 2 * atan2(sqrt(a), sqrt(1 - a))

        distance = R * c

        print("Result: ", distance)
        print("Should be: ", 278.546, "km")
    """
    earth_radius = 6373.0

    client_lat, client_lon = radians(float(client_lat)), radians(float(client_lon))
    if not client_lat:
        return qs.annotate(
            distance=Value(0),
        )

    return qs.annotate(
        rlat=Radians('latitude'),
        rlon=Radians('longitude'),

        # a=sin(dlat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(dlon / 2) ** 2
        # c = 2 * atan2(sqrt(a), sqrt(1 - a))
        lat_diff=F('rlat') - client_lat,
        lon_diff=F('rlon') - client_lon,
        a=Sin(F('lat_diff') / 2.0) ** 2.0 + Cos(client_lat) * Cos(F('rlat')) * Sin(
            F('lon_diff') / 2.0) ** 2.0,
        c=2.0 * ATan2(Sqrt(F('a')), Sqrt(1.0 - F('a'))),
        distance=F('c') * earth_radius
    )