"""汇率服务：CNY→RUB。数据源三级降级（FloatRates → 俄央行 → 兜底），服务端缓存。"""
from __future__ import annotations

import time

import httpx

_FALLBACK_RATE = 11.5
_MIN, _MAX = 5.0, 25.0
_CACHE_TTL = 3600  # 秒

_cache: dict = {"rate": None, "source": "", "ts": 0.0}


def _valid(rate: float) -> bool:
    return _MIN <= rate <= _MAX


async def _fetch_floatrates() -> float | None:
    async with httpx.AsyncClient(timeout=10.0, follow_redirects=True) as client:
        resp = await client.get("https://www.floatrates.com/daily/cny.json")
        resp.raise_for_status()
        rub = resp.json().get("rub", {})
        rate = rub.get("rate")
        return float(rate) if rate else None


async def _fetch_cbr() -> float | None:
    async with httpx.AsyncClient(timeout=10.0, follow_redirects=True) as client:
        resp = await client.get("https://www.cbr-xml-daily.ru/daily_json.js")
        resp.raise_for_status()
        cny = resp.json().get("Valute", {}).get("CNY", {})
        value = cny.get("Value")
        return float(value) if value else None


async def get_fx_rate() -> dict:
    """返回 {rate, source, updated_at}。带 1 小时内存缓存。"""
    now = time.time()
    if _cache["rate"] and (now - _cache["ts"]) < _CACHE_TTL:
        return dict(_cache)

    rate = None
    source = ""
    for name, fn in (("floatrates", _fetch_floatrates), ("cbr", _fetch_cbr)):
        try:
            r = await fn()
            if r is not None and _valid(r):
                rate, source = r, name
                break
        except Exception:  # noqa: BLE001 - 数据源失败降级
            continue

    if rate is None:
        rate, source = _FALLBACK_RATE, "fallback"

    _cache.update({"rate": rate, "source": source, "ts": now})
    return dict(_cache)