from __future__ import annotations

from dataclasses import dataclass
from math import asin, cos, radians, sin, sqrt

from pyproj import Geod

WGS84_GEOD = Geod(ellps="WGS84")
EARTH_RADIUS_M = 6_371_000.0


@dataclass(frozen=True)
class GeoPoint:
    lat: float
    lon: float


@dataclass(frozen=True)
class PathPoint(GeoPoint):
    distance_m: float


def haversine(a: GeoPoint, b: GeoPoint) -> float:
    lat1 = radians(a.lat)
    lat2 = radians(b.lat)
    dlat = radians(b.lat - a.lat)
    dlon = radians(b.lon - a.lon)
    h = sin(dlat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(dlon / 2) ** 2
    return 2 * EARTH_RADIUS_M * asin(sqrt(h))


def sample_path(start: GeoPoint, end: GeoPoint, n: int) -> list[PathPoint]:
    if n < 2:
        raise ValueError("n must be at least 2")

    _, _, total_distance = WGS84_GEOD.inv(start.lon, start.lat, end.lon, end.lat)
    inner = [] if n == 2 else WGS84_GEOD.npts(start.lon, start.lat, end.lon, end.lat, n - 2)
    coords = [(start.lon, start.lat), *inner, (end.lon, end.lat)]
    step = total_distance / (n - 1)
    return [
        PathPoint(lat=lat, lon=lon, distance_m=total_distance if i == n - 1 else i * step)
        for i, (lon, lat) in enumerate(coords)
    ]


def linestring_geojson(points: list[PathPoint]) -> dict[str, object]:
    return {
        "type": "LineString",
        "coordinates": [[point.lon, point.lat] for point in points],
    }