package services

import (
	"fmt"
	"time"

	"payment/internal/config"

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

// AuthService handles authentication operations
type AuthService struct {
	config *config.Config
}

// NewAuthService creates a new auth service
func NewAuthService(config *config.Config) *AuthService {
	return &AuthService{
		config: config,
	}
}

// Claims represents JWT claims
type Claims struct {
	ClientID uuid.UUID `json:"client_id"`
	Username string    `json:"username"`
	jwt.RegisteredClaims
}

// GenerateToken generates a JWT token for a client
func (s *AuthService) GenerateToken(clientID uuid.UUID, username string) (string, error) {
	claims := &Claims{
		ClientID: clientID,
		Username: username,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(time.Duration(s.config.JWT.ExpiryHours) * time.Hour)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			NotBefore: jwt.NewNumericDate(time.Now()),
			Issuer:    "payment-service",
			Subject:   clientID.String(),
		},
	}

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

// ValidateToken validates a JWT token
func (s *AuthService) ValidateToken(tokenString string) (*Claims, error) {
	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
		}
		return []byte(s.config.JWT.Secret), nil
	})

	if err != nil {
		return nil, err
	}

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

	return nil, fmt.Errorf("invalid token")
}

// ExtractClientID extracts client ID from token
func (s *AuthService) ExtractClientID(tokenString string) (uuid.UUID, error) {
	claims, err := s.ValidateToken(tokenString)
	if err != nil {
		return uuid.Nil, err
	}
	return claims.ClientID, nil
}