"""좌표 거리 — 공용 한 벌."""
import math

EARTH_RADIUS_M = 6_371_000.0


def haversine_m(lat1: float, lng1: float, lat2: float, lng2: float) -> float:
    """두 좌표(위도, 경도) 사이의 거리(m)."""
    p1, p2 = math.radians(lat1), math.radians(lat2)
    dp, dl = math.radians(lat2 - lat1), math.radians(lng2 - lng1)
    a = math.sin(dp / 2) ** 2 + math.cos(p1) * math.cos(p2) * math.sin(dl / 2) ** 2
    return 2 * EARTH_RADIUS_M * math.asin(math.sqrt(a))


def haversine_km(lat1: float, lng1: float, lat2: float, lng2: float) -> float:
    return haversine_m(lat1, lng1, lat2, lng2) / 1000.0