"""
会话密钥服务

提供动态会话密钥的生成、存储和验证功能
"""
import os
import time
import secrets
from typing import Dict, Optional, Tuple


class SessionKeyService:
    """会话密钥服务类"""
    
    def __init__(self):
        # 存储会话密钥的内存字典，格式：{key_id: (key, expiry_time)}
        self.session_keys: Dict[str, Tuple[str, float]] = {}
        # 密钥有效期（秒）
        self.key_expiry_seconds = 180  # 3分钟
    
    def generate_session_key(self) -> Tuple[str, str]:
        """
        生成会话密钥
        
        Returns:
            Tuple[str, str]: (key_id, session_key)
        """
        # 生成唯一的key_id
        key_id = secrets.token_urlsafe(16)
        # 生成32位的AES密钥
        session_key = secrets.token_hex(16)  # 16字节 = 32字符
        # 计算过期时间
        expiry_time = time.time() + self.key_expiry_seconds
        # 存储密钥
        self.session_keys[key_id] = (session_key, expiry_time)
        # 清理过期密钥
        self._clean_expired_keys()
        return key_id, session_key
    
    def get_session_key(self, key_id: str) -> Optional[str]:
        """
        获取会话密钥
        
        Args:
            key_id: 密钥ID
            
        Returns:
            Optional[str]: 会话密钥，如果不存在或已过期则返回None
        """
        # 清理过期密钥
        self._clean_expired_keys()
        # 获取密钥
        key_info = self.session_keys.get(key_id)
        if not key_info:
            return None
        
        session_key, expiry_time = key_info
        # 检查是否过期
        if time.time() > expiry_time:
            # 删除过期密钥
            del self.session_keys[key_id]
            return None
        
        # 确保返回的会话密钥是字符串类型
        return str(session_key)
    
    def remove_session_key(self, key_id: str) -> None:
        """
        删除会话密钥
        
        Args:
            key_id: 密钥ID
        """
        if key_id in self.session_keys:
            del self.session_keys[key_id]
    
    def _clean_expired_keys(self) -> None:
        """
        清理过期的会话密钥
        """
        current_time = time.time()
        expired_keys = [
            key_id for key_id, (_, expiry_time) in self.session_keys.items()
            if current_time > expiry_time
        ]
        for key_id in expired_keys:
            del self.session_keys[key_id]


# 全局实例
session_key_service = SessionKeyService()