"""City search (offline, geonamescache) + historical timezone resolution."""
from datetime import datetime
from zoneinfo import ZoneInfo

import geonamescache
from timezonefinder import TimezoneFinder

_gc = geonamescache.GeonamesCache()
_tf = TimezoneFinder()
_countries = {c["iso"]: c["name"] for c in _gc.get_countries().values()}

_CITY_INDEX = None


def _index():
    global _CITY_INDEX
    if _CITY_INDEX is None:
        rows = []
        for c in _gc.get_cities().values():
            rows.append({
                "name": c["name"],
                "search": c["name"].lower(),
                "alt": [a.lower() for a in c.get("alternatenames", [])[:20]],
                "country": _countries.get(c["countrycode"], c["countrycode"]),
                "cc": c["countrycode"],
                "admin": c.get("admin1code", ""),
                "lat": c["latitude"],
                "lon": c["longitude"],
                "pop": c["population"],
                "tz": c["timezone"],
            })
        rows.sort(key=lambda r: -r["pop"])
        _CITY_INDEX = rows
    return _CITY_INDEX


def search_cities(q, limit=12):
    q = q.strip().lower()
    if len(q) < 2:
        return []
    starts, contains = [], []
    for r in _index():
        if r["search"].startswith(q):
            starts.append(r)
        elif q in r["search"] or any(a.startswith(q) for a in r["alt"]):
            contains.append(r)
        if len(starts) >= limit:
            break
    rows = (starts + contains)[:limit]
    return [{"name": r["name"], "country": r["country"], "cc": r["cc"],
             "admin": r["admin"], "lat": r["lat"], "lon": r["lon"], "tz": r["tz"],
             "label": f'{r["name"]}, {r["country"]}'} for r in rows]


def resolve_offset(lat, lon, year, month, day, hour, minute, tz_hint=None):
    """Return (utc_offset_hours, tz_name) for the LOCAL wall-clock birth time.

    Uses the IANA tz database, which carries historical offsets and DST rules —
    the same thing the 90s programs shipped as their 'atlas'.
    """
    tzname = tz_hint or _tf.timezone_at(lat=lat, lng=lon)
    if not tzname:
        tzname = _tf.closest_timezone_at(lat=lat, lng=lon) if hasattr(_tf, "closest_timezone_at") else "UTC"
    tz = ZoneInfo(tzname)
    local = datetime(year, month, day, hour, minute, tzinfo=tz)
    off = local.utcoffset().total_seconds() / 3600.0
    return off, tzname