"""Terrain elevation via Open-Meteo (cached per coordinate)."""

from __future__ import annotations

import logging
from typing import Optional

import httpx

logger = logging.getLogger(__name__)

_CACHE: dict[tuple[float, float], Optional[float]] = {}
_TIMEOUT = 3.0


def _cache_key(lat: float, lon: float) -> tuple[float, float]:
    return (round(lat, 4), round(lon, 4))


def fetch_elevation_m(lat: float, lon: float) -> Optional[float]:
    key = _cache_key(lat, lon)
    if key in _CACHE:
        return _CACHE[key]
    try:
        with httpx.Client(timeout=_TIMEOUT) as client:
            r = client.get(
                "https://api.open-meteo.com/v1/elevation",
                params={"latitude": lat, "longitude": lon},
            )
            r.raise_for_status()
            data = r.json()
            elevations = data.get("elevation") or []
            if elevations:
                val = float(elevations[0])
                _CACHE[key] = val
                return val
    except Exception as e:
        logger.warning("open-meteo elevation failed for %s,%s: %s", lat, lon, e)
    _CACHE[key] = None
    return None