package auth

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"time"

	"github.com/golang-jwt/jwt/v5"
	gossh "golang.org/x/crypto/ssh"
)

// Claims represents the JWT claims
type Claims struct {
	UserID   uint   `json:"user_id"`
	Email    string `json:"email"`
	Username string `json:"username"`
	jwt.RegisteredClaims
}

// JWTManager handles JWT token generation and validation
type JWTManager struct {
	secretKey     string
	tokenDuration time.Duration
}

// NewJWTManager creates a new JWT manager
func NewJWTManager(secretKey string, tokenDuration time.Duration) *JWTManager {
	return &JWTManager{
		secretKey:     secretKey,
		tokenDuration: tokenDuration,
	}
}

// GenerateToken generates a new JWT token for a user
func (m *JWTManager) GenerateToken(userID uint, email, username string) (string, error) {
	claims := Claims{
		UserID:   userID,
		Email:    email,
		Username: username,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(m.tokenDuration)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			NotBefore: jwt.NewNumericDate(time.Now()),
			Issuer:    "terminalshop",
		},
	}

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

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

	if err != nil {
		return nil, err
	}

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

	return nil, errors.New("invalid token")
}

// GetSSHKeyFingerprint returns the MD5 fingerprint of an SSH public key
// This matches the format shown by `ssh-keygen -lf ~/.ssh/id_rsa.pub`
func GetSSHKeyFingerprint(pubKey gossh.PublicKey) string {
	hash := sha256.Sum256(pubKey.Marshal())
	return "SHA256:" + hex.EncodeToString(hash[:])
}

// FormatSSHPublicKey formats an SSH public key in authorized_keys format
func FormatSSHPublicKey(pubKey gossh.PublicKey) string {
	return string(gossh.MarshalAuthorizedKey(pubKey))
}