"""Geo helpers: ZIP geocoding, haversine distance, bounding-box radius filter.

Portable across MySQL and SQLite (no spatial extension needed). For large-scale
deployments, see README for the MySQL POINT + SPATIAL INDEX upgrade.
"""
import math
from app.extensions import db
from app.models.geo import ZipGeo

EARTH_MI = 3958.7613  # mean earth radius, miles


def geocode_zip(zip_code):
    """Return (lat, lng, city, state, metro) or None."""
    row = db.session.get(ZipGeo, (zip_code or "").strip())
    if row is None:
        return None
    return row.lat, row.lng, row.city, row.state, row.metro


def haversine_mi(lat1, lng1, lat2, lng2):
    rlat1, rlat2 = math.radians(lat1), math.radians(lat2)
    dlat = math.radians(lat2 - lat1)
    dlng = math.radians(lng2 - lng1)
    a = (math.sin(dlat / 2) ** 2
         + math.cos(rlat1) * math.cos(rlat2) * math.sin(dlng / 2) ** 2)
    return EARTH_MI * 2 * math.asin(math.sqrt(a))


def bounding_box(lat, lng, radius_mi):
    """Lat/lng min/max box enclosing the radius. Cheap indexed prefilter."""
    lat_delta = radius_mi / 69.0
    # guard against poles; cos(lat) shrinks lng degrees-per-mile
    cos_lat = max(math.cos(math.radians(lat)), 0.01)
    lng_delta = radius_mi / (69.172 * cos_lat)
    return (lat - lat_delta, lat + lat_delta, lng - lng_delta, lng + lng_delta)