"""LLM Key 兜底：主 Key 余额不足（402 Insufficient Balance）时自动切到兜底 Key。

- 主 Key：设置页保存的 llm_api_key / .env 的 DEEPSEEK_API_KEY（千问：DASHSCOPE_API_KEY）
- 兜底 Key：.env 的 DEEPSEEK_API_KEY_FALLBACK / DASHSCOPE_API_KEY_FALLBACK
- 切换状态记在 settings 表 `llm_primary_exhausted_at`，重启不丢；超过 LLM_PRIMARY_RETRY_HOURS 后下一次调用先试主 Key，
  仍 402 就再记一次（代价是每个重试周期一次失败调用）。

三条调用路径都走这里：NLU / 沉淀提炼（nlu._call_llm）、Agent（llm_factory.FallbackChatModel）。
"""

from __future__ import annotations

import logging
from datetime import datetime, timedelta

from backend.config import settings
from backend.db import database as db

logger = logging.getLogger(__name__)

EXHAUSTED_KEY = "llm_primary_exhausted_at"
_TIME_FMT = "%Y-%m-%d %H:%M:%S"

# 进程内缓存，避免每次调用都查库；跨进程以 settings 表为准
_exhausted_at: datetime | None = None
_loaded = False


def _load() -> None:
    global _exhausted_at, _loaded
    if _loaded:
        return
    _loaded = True
    raw = db.get_setting(EXHAUSTED_KEY)
    try:
        _exhausted_at = datetime.strptime(raw, _TIME_FMT) if raw else None
    except ValueError:
        _exhausted_at = None


def fallback_key(provider: str) -> str:
    if provider == "qwen":
        return settings.dashscope_api_key_fallback
    return settings.deepseek_api_key_fallback


def primary_exhausted() -> bool:
    """主 Key 是否仍处于「已耗尽」状态（超过重试周期视为可以再试）。"""
    _load()
    if not _exhausted_at:
        return False
    if datetime.now() - _exhausted_at > timedelta(hours=max(0.05, settings.llm_primary_retry_hours)):
        return False
    return True


def mark_primary_exhausted(reason: str = "") -> None:
    global _exhausted_at
    _load()
    _exhausted_at = datetime.now()
    db.set_setting(EXHAUSTED_KEY, _exhausted_at.strftime(_TIME_FMT))
    logger.warning("LLM 主 Key 余额不足，切到兜底 Key。%s", reason[:200])


def clear_primary_exhausted() -> None:
    """主 Key 调用成功后清掉标记（充值后自动恢复）。"""
    global _exhausted_at
    _load()
    if _exhausted_at is None:
        return
    _exhausted_at = None
    db.set_setting(EXHAUSTED_KEY, "")
    logger.info("LLM 主 Key 恢复可用")


def is_balance_error(error: BaseException | str) -> bool:
    """DeepSeek 402：{'error': {'message': 'Insufficient Balance', …}}；千问余额不足也带 402 / Arrearage。"""
    status = getattr(error, "status_code", None)
    text = str(error)
    return status == 402 or "Error code: 402" in text or "Insufficient Balance" in text or "Arrearage" in text


def choose(provider: str, primary: str) -> tuple[str, bool]:
    """返回 (本次应使用的 Key, 是否兜底)。"""
    fallback = fallback_key(provider)
    if fallback and fallback != primary and primary_exhausted():
        return fallback, True
    return primary or fallback, bool(primary == "" and fallback)


def status(provider: str, primary: str) -> dict:
    _load()
    fallback = fallback_key(provider)
    _key, using = choose(provider, primary)
    return {
        "fallback_configured": bool(fallback),
        "using_fallback": using,
        "primary_exhausted_at": _exhausted_at.strftime(_TIME_FMT) if _exhausted_at else None,
        "retry_hours": settings.llm_primary_retry_hours,
    }