package middleware

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"net/http"
	"server/internal/config"
	"server/internal/pkg/errs"
	"server/internal/pkg/httputil"
	"strings"
	"time"

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

type JWTMiddleware struct {
	cfg *config.JWTConfig
}

type Claims struct {
	UserID       int32 `json:"user_id"`
	TokenVersion int32 `json:"token_version"`
	jwt.RegisteredClaims
}

func NewJWTMiddleware(cfg *config.Config) (*JWTMiddleware, error) {
	jwtCfg := cfg.JWTConfig

	// 不允许空密钥
	if jwtCfg.Secret == "" {
		return nil, fmt.Errorf("jwt.secret 未配置：请在 %s.yaml 中设置 jwt.secret", config.GetEnv())
	}

	m := &JWTMiddleware{cfg: &jwtCfg}

	// 启动时校验签名算法配置
	if _, err := m.signingMethod(); err != nil {
		return nil, err
	}

	return m, nil
}

// signingMethod 返回配置的签名算法（仅支持 HMAC 家族）
func (m *JWTMiddleware) signingMethod() (jwt.SigningMethod, error) {
	switch strings.ToUpper(m.cfg.SigningMethod) {
	case "", "HS256":
		return jwt.SigningMethodHS256, nil
	case "HS384":
		return jwt.SigningMethodHS384, nil
	case "HS512":
		return jwt.SigningMethodHS512, nil
	default:
		return nil, fmt.Errorf("不支持的 jwt.signing_method: %q（仅支持 HS256/HS384/HS512）", m.cfg.SigningMethod)
	}
}

// ParseToken 解析accessToken
func (m *JWTMiddleware) ParseToken(tokenStr string) (*Claims, error) {
	token, err := jwt.ParseWithClaims(
		tokenStr,
		&Claims{},
		func(token *jwt.Token) (any, error) {
			return []byte(m.cfg.Secret), nil
		},
	)

	if err != nil || !token.Valid {
		return nil, errs.ErrInvalidToken
	}

	claims, ok := token.Claims.(*Claims)
	if !ok {
		return nil, errs.ErrInvalidTokenClaims
	}

	if claims.UserID == 0 {
		return nil, errs.ErrInvalidTokenClaims
	}

	return claims, nil
}

func (m *JWTMiddleware) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		auth := r.Header.Get("Authorization")

		if auth == "" {
			httputil.Fail(w, errs.ErrUnauthenticated)
			return
		}

		parts := strings.SplitN(auth, " ", 2)
		if len(parts) != 2 || parts[0] != "Bearer" {
			httputil.Fail(w, errs.ErrUnauthenticated)
			return
		}

		tokenStr := parts[1]

		claims, err := m.ParseToken(tokenStr)
		if err != nil {
			httputil.Fail(w, errs.ErrInvalidToken)
			return
		}

		userCtx := GetUserContext(r.Context())
		userCtx.UserID = claims.UserID
		userCtx.TokenVersion = claims.TokenVersion

		next.ServeHTTP(w, r)
	})
}

func (m *JWTMiddleware) GenerateAccessToken(userID int32, tokenVersion int32) (string, time.Time, error) {
	method, err := m.signingMethod()
	if err != nil {
		return "", time.Time{}, err
	}

	now := time.Now()
	expiresAt := now.Add(m.cfg.Expire)

	accessClaims := Claims{
		UserID:       userID,
		TokenVersion: tokenVersion,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(expiresAt),
			IssuedAt:  jwt.NewNumericDate(now),
		},
	}

	// 使用配置的签名算法，与 ParseToken 的校验保持一致
	accessToken := jwt.NewWithClaims(method, accessClaims)
	token, err := accessToken.SignedString([]byte(m.cfg.Secret))
	if err != nil {
		return "", time.Time{}, err
	}

	return token, expiresAt, nil
}

func (m *JWTMiddleware) GenerateRefreshToken() (string, error) {
	b := make([]byte, 32)

	_, err := rand.Read(b)
	if err != nil {
		return "", err
	}

	return hex.EncodeToString(b), nil
}

// HashRefreshToken 哈希token 存储至redis
func (m *JWTMiddleware) HashRefreshToken(token string) string {
	hash := sha256.Sum256([]byte(token))
	return hex.EncodeToString(hash[:])
}