"""Offline city resolution. No requests or personal data leave the server."""
from functools import lru_cache
import unicodedata

from django.core.exceptions import ValidationError


def normalize(value):
    return ''.join(c for c in unicodedata.normalize('NFKD', value.casefold().strip()) if not unicodedata.combining(c))


@lru_cache(maxsize=1)
def gazetteer():
    import geonamescache
    return geonamescache.GeonamesCache()


def resolve_city(country, city):
    data = gazetteer()
    country_key = normalize(country)
    codes = [c['iso'] for c in data.get_countries().values() if country_key in (normalize(c['name']), c['iso'].lower(), c['iso3'].lower())]
    if not codes:
        raise ValidationError({'country': 'Enter a country name or ISO code, e.g. Canada or CA.'})
    city_key = normalize(city)
    country_cities = [c for c in data.get_cities().values() if c['countrycode'] in codes]
    # Prefer the city's canonical name over another town's historical aliases.
    # E.g. Tehran is also listed as an alias of Tiran in GeoNames.
    matches = [c for c in country_cities if normalize(c['name']) == city_key]
    if not matches:
        matches = [c for c in country_cities if city_key in {
            normalize(alias) for alias in c.get('alternatenames', [])
        }]
    if len(matches) != 1:
        raise ValidationError({'city': 'City not found or ambiguous. Use coordinates for small towns or cities with the same name.'})
    return matches[0]['latitude'], matches[0]['longitude']