package auth

import (
	"errors"
	"fmt"
	"time"

	"yinli-api/pkg/config"

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

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

// GenerateToken 生成JWT令牌
func GenerateToken(userID uint, username string) (string, error) {
	cfg := config.AppConfig
	if cfg == nil {
		return "", errors.New("配置未初始化")
	}

	now := time.Now()
	claims := Claims{
		UserID:   userID,
		Username: username,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(now.Add(time.Duration(cfg.JWT.ExpireHours) * time.Hour)),
			IssuedAt:  jwt.NewNumericDate(now),
			NotBefore: jwt.NewNumericDate(now),
			Issuer:    "yinli-api",
			Subject:   fmt.Sprintf("%d", userID),
		},
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString([]byte(cfg.JWT.Secret))
}

// ParseToken 解析JWT令牌
func ParseToken(tokenString string) (*Claims, error) {
	cfg := config.AppConfig
	if cfg == nil {
		return nil, errors.New("配置未初始化")
	}

	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("意外的签名方法: %v", token.Header["alg"])
		}
		return []byte(cfg.JWT.Secret), nil
	})

	if err != nil {
		return nil, err
	}

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

	return nil, errors.New("无效的令牌")
}

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

	// 检查令牌是否过期
	if claims.ExpiresAt != nil && claims.ExpiresAt.Time.Before(time.Now()) {
		return nil, errors.New("令牌已过期")
	}

	return claims, nil
}

// RefreshToken 刷新JWT令牌
func RefreshToken(tokenString string) (string, error) {
	claims, err := ParseToken(tokenString)
	if err != nil {
		return "", err
	}

	// 检查令牌是否在刷新窗口内
	cfg := config.AppConfig
	refreshWindow := time.Duration(cfg.JWT.ExpireHours/2) * time.Hour
	if claims.ExpiresAt != nil && time.Until(claims.ExpiresAt.Time) > refreshWindow {
		return "", errors.New("令牌还未到刷新时间")
	}

	return GenerateToken(claims.UserID, claims.Username)
}

// ExtractTokenFromHeader 从请求头中提取令牌
func ExtractTokenFromHeader(authHeader string) (string, error) {
	if authHeader == "" {
		return "", errors.New("授权头为空")
	}

	const bearerPrefix = "Bearer "
	if len(authHeader) < len(bearerPrefix) || authHeader[:len(bearerPrefix)] != bearerPrefix {
		return "", errors.New("无效的授权头格式")
	}

	return authHeader[len(bearerPrefix):], nil
}

// GetUserIDFromToken 从令牌中获取用户ID
func GetUserIDFromToken(tokenString string) (uint, error) {
	claims, err := ValidateToken(tokenString)
	if err != nil {
		return 0, err
	}
	return claims.UserID, nil
}

// GetUsernameFromToken 从令牌中获取用户名
func GetUsernameFromToken(tokenString string) (string, error) {
	claims, err := ValidateToken(tokenString)
	if err != nil {
		return "", err
	}
	return claims.Username, nil
}