import jwt
import datetime
from functools import wraps
from flask import request, current_app
from app.model.user_model import User
from app import db

class JWTUtils:
    @staticmethod
    def generate_token(user_id: int, username: str, expires_in: int = 3600):
        """
        生成JWT token
        
        Args:
            user_id: 用户ID
            username: 用户名
            expires_in: token过期时间（秒），默认1小时
        
        Returns:
            str: JWT token
        """
        payload = {
            'user_id': user_id,
            'username': username,
            'iat': datetime.datetime.utcnow()
        }
        # 仅当 expires_in > 0 时设置过期时间；<=0 表示永不过期
        if isinstance(expires_in, int) and expires_in > 0:
            payload['exp'] = datetime.datetime.utcnow() + datetime.timedelta(seconds=expires_in)
        
        token = jwt.encode(payload, current_app.config['SECRET_KEY'], algorithm='HS256')
        return token

    @staticmethod
    def verify_token(token: str):
        """
        验证JWT token
        
        Args:
            token: JWT token字符串
        
        Returns:
            dict: token payload，如果验证失败则返回None
        """
        try:
            payload = jwt.decode(token, current_app.config['SECRET_KEY'], algorithms=['HS256'])
            return payload
        except jwt.ExpiredSignatureError:
            return None
        except jwt.InvalidTokenError:
            return None

    @staticmethod
    def get_current_user():
        """
        从请求头中获取当前用户
        
        Returns:
            User: 当前用户对象，如果未认证则返回None
        """
        auth_header = request.headers.get('Authorization')
        if not auth_header:
            return None
        
        try:
            # 期望格式: "Bearer <token>"
            token = auth_header.split(' ')[1]
        except IndexError:
            return None
        
        payload = JWTUtils.verify_token(token)
        if not payload:
            return None
        
        user_id = payload.get('user_id')
        if not user_id:
            return None
        
        return db.session.query(User).get(user_id)

def token_required(f):
    """
    JWT认证装饰器
    
    使用方法:
    @token_required
    def protected_route():
        # 当前用户可以通过 g.current_user 访问
        pass
    """
    @wraps(f)
    def decorated(*args, **kwargs):
        from flask import g
        
        auth_header = request.headers.get('Authorization')
        if not auth_header:
            return {'message': '缺少认证token'}, 401
        
        try:
            # 期望格式: "Bearer <token>"
            token = auth_header.split(' ')[1]
        except IndexError:
            return {'message': '认证token格式错误'}, 401
        
        payload = JWTUtils.verify_token(token)
        if not payload:
            return {'message': '认证token无效或已过期'}, 401
        
        user_id = payload.get('user_id')
        if not user_id:
            return {'message': '认证token无效'}, 401
        
        # 获取用户信息
        user = db.session.query(User).get(user_id)
        if not user or not user.is_active:
            return {'message': '用户不存在或已被禁用'}, 401
        
        # 将用户信息存储到g对象中，供视图函数使用
        g.current_user = user
        return f(*args, **kwargs)
    
    return decorated

def admin_required(f):
    """
    管理员权限装饰器（可以扩展用户角色功能）
    
    使用方法:
    @admin_required
    def admin_route():
        pass
    """
    @wraps(f)
    def decorated(*args, **kwargs):
        from flask import g
        
        if not hasattr(g, 'current_user') or not g.current_user:
            return jsonify({'message': '需要管理员权限'}), 403
        
        # 这里可以添加角色检查逻辑
        # 目前简单检查用户名是否为admin
        if g.current_user.username != 'admin':
            return jsonify({'message': '需要管理员权限'}), 403
        
        return f(*args, **kwargs)
    
    return decorated