import string
import random
from sqlalchemy.orm import Session
from app.core.biz_exception import NotFoundError, PermissionDeniedError, BizLogicError
from app.models.short_url import ShortUrl


class ShortUrlService:
    @staticmethod
    def generate_short_key(length: int = 8) -> str:
        """生成随机短 Key（由字母+数字组成）"""
        chars = string.ascii_letters + string.digits
        return ''.join(random.choices(chars, k=length))

    @staticmethod
    def create_short_url(db: Session, long_url: str) -> ShortUrl:
        """创建短链接"""
        # 检查是否已经存在相同的长链接
        existing = db.query(ShortUrl).filter(ShortUrl.long_url == long_url).first()
        if existing:
            raise BizLogicError("Short url already exist")

        # 生成唯一 short_key
        short_key = ShortUrlService.generate_short_key()
        while db.query(ShortUrl).filter(ShortUrl.short_key == short_key).first():
            short_key = ShortUrlService.generate_short_key()

        db_obj = ShortUrl(short_key=short_key, long_url=long_url)
        db.add(db_obj)
        db.commit()
        db.refresh(db_obj)
        return db_obj

    @staticmethod
    def get_long_url(db: Session, short_key: str) -> str:
        """通过短 key 获取原始长链接"""
        record = db.query(ShortUrl).filter(ShortUrl.short_key == short_key).first()
        if not record:
            raise NotFoundError("Short url not found")
        return record.long_url