package jwt

import (
	"errors"
	"time"

	"github.com/golang-jwt/jwt/v5"
)

var (
	ErrInvalidToken = errors.New("invalid token")
	ErrExpiredToken = errors.New("token has expired")
)

// Claims JWT 声明
type Claims struct {
	UserID   string `json:"user_id"`
	Username string `json:"username"`
	jwt.RegisteredClaims
}

// JWT JWT工具
type JWT struct {
	secretKey          string
	accessTokenExpire  time.Duration
	refreshTokenExpire time.Duration
}

// New 创建JWT实例
func New(secret string, accessExpire, refreshExpire time.Duration) *JWT {
	return &JWT{
		secretKey:          secret,
		accessTokenExpire:  accessExpire,
		refreshTokenExpire: refreshExpire,
	}
}

// GenerateAccessToken 生成访问令牌
func (j *JWT) GenerateAccessToken(userID, username string) (string, error) {
	now := time.Now()
	claims := Claims{
		UserID:   userID,
		Username: username,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(now.Add(j.accessTokenExpire)),
			IssuedAt:  jwt.NewNumericDate(now),
			NotBefore: jwt.NewNumericDate(now),
			Issuer:    "carrot_bbs",
		},
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString([]byte(j.secretKey))
}

// GenerateRefreshToken 生成刷新令牌
func (j *JWT) GenerateRefreshToken(userID, username string) (string, error) {
	now := time.Now()
	claims := Claims{
		UserID:   userID,
		Username: username,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(now.Add(j.refreshTokenExpire)),
			IssuedAt:  jwt.NewNumericDate(now),
			NotBefore: jwt.NewNumericDate(now),
			Issuer:    "carrot_bbs",
			ID:        "refresh",
		},
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString([]byte(j.secretKey))
}

// ParseToken 解析令牌
func (j *JWT) ParseToken(tokenString string) (*Claims, error) {
	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
		return []byte(j.secretKey), nil
	})

	if err != nil {
		return nil, err
	}

	if claims, ok := token.Claims.(*Claims); ok && token.Valid {
		return claims, nil
	}

	return nil, ErrInvalidToken
}

// ValidateToken 验证令牌
func (j *JWT) ValidateToken(tokenString string) error {
	claims, err := j.ParseToken(tokenString)
	if err != nil {
		return err
	}

	// 检查是否是刷新令牌
	if claims.ID == "refresh" {
		return errors.New("cannot use refresh token as access token")
	}

	return nil
}