"""WGS84 geodesic helpers — Vincenty distance + bearing for accuracy assertions.

Wraps `pyproj.Geod` (WGS84 ellipsoid) for the few operations the blackbox
tests need. Kept deliberately small — broader geo math (UTM, MGRS, datum
conversions) is NOT in scope for the e2e harness.

All inputs are degrees lat / lon (WGS84); all distances are meters.
"""

from __future__ import annotations

from dataclasses import dataclass

from pyproj import Geod

_WGS84 = Geod(ellps="WGS84")


@dataclass(frozen=True)
class GeodeticDelta:
    """Bearing + distance + back-bearing between two WGS84 points."""

    distance_m: float
    forward_bearing_deg: float
    reverse_bearing_deg: float


def distance_m(lat1: float, lon1: float, lat2: float, lon2: float) -> float:
    """Vincenty distance in meters between two WGS84 points.

    Raises ValueError on NaN inputs (defensive — silent NaN propagation in
    a test assertion is the kind of bug this helper exists to prevent).
    """
    for name, value in (("lat1", lat1), ("lon1", lon1), ("lat2", lat2), ("lon2", lon2)):
        if value != value:  # NaN check
            raise ValueError(f"distance_m: {name} is NaN")
    _, _, d = _WGS84.inv(lon1, lat1, lon2, lat2)
    return float(d)


def delta(lat1: float, lon1: float, lat2: float, lon2: float) -> GeodeticDelta:
    """Full geodetic delta: distance + forward/reverse bearings."""
    fwd_az, rev_az, d = _WGS84.inv(lon1, lat1, lon2, lat2)
    return GeodeticDelta(
        distance_m=float(d),
        forward_bearing_deg=float(fwd_az),
        reverse_bearing_deg=float(rev_az),
    )


def offset(lat: float, lon: float, bearing_deg: float, distance_m: float) -> tuple[float, float]:
    """Project ``(lat, lon)`` by ``distance_m`` along ``bearing_deg`` (degrees CW from north)."""
    new_lon, new_lat, _ = _WGS84.fwd(lon, lat, bearing_deg, distance_m)
    return float(new_lat), float(new_lon)