diary-news/backend/app/services/translation/service.py

"""翻译服务门面:配额检查 + 缓存 + 引擎选择 + 月度计数。"""
from __future__ import annotations

import asyncio
import hashlib
import logging
from datetime import datetime, timezone
from typing import Protocol

from app.config import settings
from app.redis_client import get_redis
from app.services.translation.base import BaseTranslator, TranslationResult
from app.services.translation.local import LocalTranslator
from app.services.translation.tencent import TencentTranslator

logger = logging.getLogger("news.translate.service")


# 缓存 key
def _cache_key(text: str, src: str, tgt: str) -> str:
    h = hashlib.sha1(f"{src}|{tgt}|{text}".encode()).hexdigest()
    return f"translation:cache:{h}"


def _month_key() -> str:
    now = datetime.now(timezone.utc)
    return f"translation:month:{now:%Y%m}"


class TranslationService:
    def __init__(self):
        self._tencent: BaseTranslator | None = None
        self._local: BaseTranslator | None = None
        self._sem = asyncio.Semaphore(3)  # 并发限流

    def _primary(self) -> BaseTranslator:
        if self._tencent is None:
            self._tencent = TencentTranslator()
        return self._tencent

    def _fallback(self) -> BaseTranslator | None:
        if self._local is None and settings.local_translate_enabled:
            try:
                self._local = LocalTranslator()
            except Exception as e:
                logger.warning("local translator init failed: %s", e)
                self._local = None
        return self._local

    async def can_use_tencent(self, chars: int) -> bool:
        if not settings.tencentcloud_secret_id:
            return False
        r = get_redis()
        used = int(await r.get(_month_key()) or 0)
        buffered = int(
            settings.tencent_tmt_quota_month * (1 - settings.tencent_tmt_quota_buffer)
        )
        return (used + chars) <= buffered

    async def add_usage(self, chars: int) -> None:
        r = get_redis()
        key = _month_key()
        now = datetime.now(timezone.utc)
        # 下个月第一天
        if now.month == 12:
            next_month = now.replace(year=now.year + 1, month=1, day=1)
        else:
            next_month = now.replace(month=now.month + 1, day=1, hour=0, minute=0, second=0, microsecond=0)
        ttl = max(60, int((next_month - now).total_seconds()) + 86400)  # +1 天 buffer
        async with r.pipeline(transaction=False) as pipe:
            pipe.incrby(key, chars)
            pipe.expire(key, ttl)
            await pipe.execute()

    async def translate(
        self, text: str, source: str = "auto", target: str = "zh"
    ) -> TranslationResult:
        if not text.strip():
            return TranslationResult(text=text, engine="skip", chars=0)

        chars = len(text)
        # 1) 缓存
        r = get_redis()
        ck = _cache_key(text, source, target)
        cached = await r.get(ck)
        if cached is not None:
            return TranslationResult(text=cached, engine="cache", chars=chars, cached=True)

        # 2) 选引擎
        use_tencent = await self.can_use_tencent(chars)
        engine: BaseTranslator
        if use_tencent:
            engine = self._primary()
        else:
            fb = self._fallback()
            if fb is None:
                # 没本地:返回原文 + 标记
                return TranslationResult(
                    text=text + "\n\n[本条未翻译:配额耗尽且未启用本地翻译]",
                    engine="skip",
                    chars=chars,
                )
            engine = fb
            logger.info("fallback to local translator for %d chars", chars)

        # 3) 调用
        async with self._sem:
            res = None
            try:
                res = await engine.translate(text, source=source, target=target)
            except Exception as e:
                # 失败:降级
                logger.exception("translate failed with %s: %s", engine.name, e)
                fb = self._fallback()
                if fb is not None and engine is not fb:
                    try:
                        res = await fb.translate(text, source=source, target=target)
                    except Exception as e2:
                        logger.exception("fallback %s also failed: %s", fb.name, e2)
                        res = None
            if res is None:
                # 主 + fallback 都失败:抛异常,让上层标记 status=failed
                raise RuntimeError(f"translation failed for {chars} chars (engine={engine.name})")

        # 4) 写缓存(无论引擎)
        try:
            await r.set(ck, res.text, ex=60 * 60 * 24 * 30)  # 30 天
        except Exception:
            pass

        # 5) 计数(只在 tencent 上计)
        if res.engine == "tencent":
            try:
                await self.add_usage(res.chars or chars)
            except Exception as e:
                logger.warning("add_usage failed: %s", e)

        return res


# 全局单例
service = TranslationService()


# 让后端 worker 直接调
class _Protocol(Protocol):
    async def translate(self, text: str, source: str = "auto", target: str = "zh") -> TranslationResult: ...