from __future__ import annotations

import json
import os
from functools import lru_cache
from typing import List, Tuple, Dict, Optional

from django.conf import settings


def _json_path(filename: str) -> str:
    return os.path.join(settings.BASE_DIR, 'static', 'json', filename)


@lru_cache(maxsize=1)
def load_countries() -> List[dict]:
    with open(_json_path('countries.json'), 'r', encoding='utf-8') as f:
        return json.load(f)


@lru_cache(maxsize=1)
def load_states() -> List[dict]:
    with open(_json_path('states.json'), 'r', encoding='utf-8') as f:
        return json.load(f)


@lru_cache(maxsize=1)
def load_cities() -> List[dict]:
    with open(_json_path('cities.json'), 'r', encoding='utf-8') as f:
        return json.load(f)


@lru_cache(maxsize=1)
def _index_states_by_country() -> Dict[str, List[Tuple[str, str]]]:
    idx: Dict[str, List[Tuple[str, str]]] = {}
    for s in load_states():
        cc = s.get('country_code')
        code = s.get('iso2') or s.get('state_code')
        name = s.get('name')
        if not (cc and code and name):
            continue
        idx.setdefault(cc, []).append((str(code), name))
    return idx


@lru_cache(maxsize=1)
def _index_cities_by_country_state() -> Dict[Tuple[str, str], List[Tuple[str, str]]]:
    idx: Dict[Tuple[str, str], List[Tuple[str, str]]] = {}
    for c in load_cities():
        cc = c.get('country_code')
        sc = (c.get('state_code') or '').upper()
        name = c.get('name')
        if not (cc and sc and name):
            continue
        key = (cc, sc)
        idx.setdefault(key, []).append((name, name))
    return idx


def country_label(code: str) -> Optional[str]:
    code = (code or '').upper()
    for c in load_countries():
        if c.get('iso2') == code:
            return c.get('name')
    return None


def state_label(country_code: str, state_code: str) -> Optional[str]:
    cc = (country_code or '').upper()
    sc = (state_code or '').upper()
    for s in load_states():
        if s.get('country_code') == cc and s.get('iso2', '').upper() == sc:
            return s.get('name')
        if s.get('country_code') == cc and s.get('state_code', '').upper() == sc:
            return s.get('name')
    return None


def list_countries(q: str | None = None) -> List[Tuple[str, str]]:
    items: List[Tuple[str, str]] = []
    ql = (q or '').strip().lower()
    for c in load_countries():
        code = c.get('iso2')
        name = c.get('name')
        if not code or not name:
            continue
        if ql and ql not in name.lower() and ql not in code.lower():
            continue
        items.append((code, name))
    return items


def list_states(country_code: str | None, q: str | None = None) -> List[Tuple[str, str]]:
    items: List[Tuple[str, str]] = []
    if not country_code:
        return items
    cc = country_code.upper()
    ql = (q or '').strip().lower()
    pool = _index_states_by_country().get(cc, [])
    if not ql:
        return list(pool)
    for code, name in pool:
        if ql and ql not in name.lower() and ql not in (code or '').lower():
            continue
        items.append((code, name))
    return items


def list_cities(country_code: str | None, state_code: str | None, q: str | None = None) -> List[Tuple[str, str]]:
    items: List[Tuple[str, str]] = []
    if not (country_code and state_code):
        return items
    cc = country_code.upper()
    sc = state_code.upper()
    ql = (q or '').strip().lower()
    pool = _index_cities_by_country_state().get((cc, sc), [])
    if not ql:
        # Return first 50 to avoid huge payloads without query
        return pool[:50]
    for code, name in pool:
        if ql in name.lower():
            items.append((code, name))
    return items