from enum import Enum

import haversine as hs


class DistanceUnit(Enum):
    """
    Enumeration of supported units.
    """

    KILOMETERS = "km"
    METERS = "m"
    MILES = "mi"


def calculate_geo_distance(point1, point2, unit=DistanceUnit.KILOMETERS):
    """Calculate the great-circle distance between two points on the Earth surface.

    Takes two 2-tuples, containing the latitude and longitude of each point in decimal degrees,
    and, optionally, a unit of length.

    :param point1: first point; tuple of (latitude, longitude) in decimal degrees
    :param point2: second point; tuple of (latitude, longitude) in decimal degrees
    :param unit: a member of geo_utils.DistanceUnit, or, equivalently, a string containing the
                 initials of its corresponding unit of measurement (i.e. miles = mi)
                 default 'km' (kilometers).

    Example: ``calculate_geo_distance((45.7597, 4.8422), (48.8567, 2.3508), unit=Unit.METERS)``

    Precondition: ``unit`` is a supported unit (supported units are listed in the `DistanceUnit` enum)

    :return: the distance between the two points in the requested unit, as a float.

    The default returned unit is kilometers. The default unit can be changed by
    setting the unit parameter to a member of ``geo_utils.DistanceUnit``
    (e.g. ``geo_utils.DistanceUnit.MILES``), or, equivalently, to a string containing the
    corresponding abbreviation (e.g. 'in'). All available units can be found in the ``DistanceUnit`` enum.
    """
    return hs.haversine(point1, point2, unit.value)