package services

import (
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"os"
	"time"

	"veza-backend-api/internal/models"

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

type JWTService struct {
	// RS256 (v0.9.1): prefer if set
	privateKey *rsa.PrivateKey
	publicKey  *rsa.PublicKey
	// HS256 fallback (dev only)
	secretKey []byte
	useRS256  bool

	issuer   string
	audience string
	Config   *models.JWTConfig
}

// NewJWTService creates a JWT service. Prefers RS256 if privateKeyPath and publicKeyPath are set.
// Falls back to HS256 with secret for development (secret must be min 32 chars).
func NewJWTService(privateKeyPath, publicKeyPath, secret, issuer, audience string) (*JWTService, error) {
	if issuer == "" {
		issuer = "veza-api"
	}
	if audience == "" {
		audience = "veza-platform"
	}

	// SECURITY(SFIX-002): ORIGIN_SECURITY_FRAMEWORK.md Rule 4 — refresh token TTL = 7 days.
	config := &models.JWTConfig{
		AccessTokenTTL:            5 * time.Minute,
		RefreshTokenTTL:           7 * 24 * time.Hour,
		RememberMeRefreshTokenTTL: 7 * 24 * time.Hour,
	}

	// Prefer RS256 if both key paths are set
	if privateKeyPath != "" && publicKeyPath != "" {
		privateKey, err := loadRSAPrivateKey(privateKeyPath)
		if err != nil {
			return nil, fmt.Errorf("load JWT private key: %w", err)
		}
		publicKey, err := loadRSAPublicKey(publicKeyPath)
		if err != nil {
			return nil, fmt.Errorf("load JWT public key: %w", err)
		}
		return &JWTService{
			privateKey: privateKey,
			publicKey:  publicKey,
			useRS256:   true,
			issuer:     issuer,
			audience:   audience,
			Config:     config,
		}, nil
	}

	// Fallback to HS256 (dev)
	if secret == "" {
		return nil, fmt.Errorf("JWT configuration required: set JWT_PRIVATE_KEY_PATH and JWT_PUBLIC_KEY_PATH (RS256), or JWT_SECRET (HS256 dev fallback)")
	}
	if len(secret) < 32 {
		return nil, fmt.Errorf("JWT secret must be at least 32 characters")
	}
	return &JWTService{
		secretKey: []byte(secret),
		useRS256:  false,
		issuer:    issuer,
		audience:  audience,
		Config:    config,
	}, nil
}

func loadRSAPrivateKey(path string) (*rsa.PrivateKey, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read private key file: %w", err)
	}
	block, _ := pem.Decode(data)
	if block == nil {
		return nil, fmt.Errorf("failed to decode PEM block")
	}
	key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		// Try PKCS8
		k, err2 := x509.ParsePKCS8PrivateKey(block.Bytes)
		if err2 != nil {
			return nil, fmt.Errorf("parse private key: %w", err)
		}
		var ok bool
		key, ok = k.(*rsa.PrivateKey)
		if !ok {
			return nil, fmt.Errorf("private key is not RSA")
		}
	}
	return key, nil
}

func loadRSAPublicKey(path string) (*rsa.PublicKey, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read public key file: %w", err)
	}
	block, _ := pem.Decode(data)
	if block == nil {
		return nil, fmt.Errorf("failed to decode PEM block")
	}
	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
		return nil, fmt.Errorf("parse public key: %w", err)
	}
	key, ok := pub.(*rsa.PublicKey)
	if !ok {
		return nil, fmt.Errorf("public key is not RSA")
	}
	return key, nil
}

func (s *JWTService) GetConfig() *models.JWTConfig {
	return s.Config
}

func (s *JWTService) sign(claims jwt.Claims) (string, error) {
	var token *jwt.Token
	if s.useRS256 {
		token = jwt.NewWithClaims(jwt.SigningMethodRS256, claims)
		return token.SignedString(s.privateKey)
	}
	token = jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(s.secretKey)
}

func (s *JWTService) GenerateAccessToken(user *models.User) (string, error) {
	claims := models.CustomClaims{
		UserID:       user.ID,
		Email:        user.Email,
		Username:     user.Username,
		Role:         user.Role,
		TokenVersion: user.TokenVersion,
		TokenType:    "access",
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(s.Config.AccessTokenTTL)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			Issuer:    s.issuer,
			Audience:  jwt.ClaimStrings{s.audience},
			ID:        uuid.NewString(),
		},
	}
	return s.sign(&claims)
}

func (s *JWTService) GenerateRefreshToken(user *models.User) (string, error) {
	claims := models.CustomClaims{
		UserID:       user.ID,
		TokenVersion: user.TokenVersion,
		IsRefresh:    true,
		TokenType:    "refresh",
		TokenFamily:  uuid.NewString(),
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(s.Config.RefreshTokenTTL)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			Issuer:    s.issuer,
			Audience:  jwt.ClaimStrings{s.audience},
			ID:        uuid.NewString(),
		},
	}
	return s.sign(&claims)
}

func (s *JWTService) GenerateTokenPair(user *models.User) (*models.TokenPair, error) {
	accessToken, err := s.GenerateAccessToken(user)
	if err != nil {
		return nil, fmt.Errorf("failed to generate access token: %w", err)
	}
	refreshToken, err := s.GenerateRefreshToken(user)
	if err != nil {
		return nil, fmt.Errorf("failed to generate refresh token: %w", err)
	}
	return &models.TokenPair{
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		ExpiresIn:    int(s.Config.AccessTokenTTL.Seconds()),
	}, nil
}

func (s *JWTService) VerifyToken(tokenString string) (*models.CustomClaims, error) {
	return s.ValidateToken(tokenString)
}

func (s *JWTService) ValidateToken(tokenString string) (*models.CustomClaims, error) {
	token, err := jwt.ParseWithClaims(tokenString, &models.CustomClaims{}, func(token *jwt.Token) (interface{}, error) {
		if s.useRS256 {
			if _, ok := token.Method.(*jwt.SigningMethodRSA); !ok {
				return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
			}
			if token.Method.Alg() != "RS256" {
				return nil, fmt.Errorf("invalid signing algorithm: %v, expected RS256", token.Method.Alg())
			}
			return s.publicKey, nil
		}
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
		}
		if token.Method.Alg() != "HS256" {
			return nil, fmt.Errorf("invalid signing algorithm: %v, expected HS256", token.Method.Alg())
		}
		return s.secretKey, nil
	},
		jwt.WithIssuer(s.issuer),
		jwt.WithAudience(s.audience),
		jwt.WithExpirationRequired(),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to parse token: %w", err)
	}
	if claims, ok := token.Claims.(*models.CustomClaims); ok && token.Valid {
		return claims, nil
	}
	return nil, fmt.Errorf("invalid token")
}

func (s *JWTService) ParseToken(tokenString string) (*models.CustomClaims, error) {
	return s.ValidateToken(tokenString)
}

func (s *JWTService) ExtractClaims(tokenString string) (*models.CustomClaims, error) {
	return s.ValidateToken(tokenString)
}

func (s *JWTService) ExtractUserID(tokenString string) (uuid.UUID, error) {
	claims, err := s.ValidateToken(tokenString)
	if err != nil {
		return uuid.Nil, fmt.Errorf("failed to extract user ID: %w", err)
	}
	return claims.UserID, nil
}

func (s *JWTService) VerifyTokenVersion(claims *models.CustomClaims, userTokenVersion int) error {
	if claims.TokenVersion != userTokenVersion {
		return fmt.Errorf("token version mismatch: token version %d does not match user version %d", claims.TokenVersion, userTokenVersion)
	}
	return nil
}

// GenerateStreamToken generates a short-lived JWT for HLS/WebSocket auth.
// Uses issuer "veza-platform" and audience "veza-services" for stream server compatibility.
func (s *JWTService) GenerateStreamToken(user *models.User) (string, error) {
	ttl := 5 * time.Minute
	now := time.Now()
	role := mapUserRoleToStreamRole(user.Role)
	claims := jwt.MapClaims{
		"sub":         user.ID.String(),
		"user_id":     user.ID.String(),
		"username":    user.Username,
		"email":       user.Email,
		"roles":       []string{role},
		"permissions": []string{"StreamAudio"},
		"exp":         now.Add(ttl).Unix(),
		"iat":         now.Unix(),
		"iss":         "veza-platform",
		"aud":         "veza-services",
		"session_id":  uuid.NewString(),
	}
	if s.useRS256 {
		token := jwt.NewWithClaims(jwt.SigningMethodRS256, claims)
		return token.SignedString(s.privateKey)
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(s.secretKey)
}

func mapUserRoleToStreamRole(role string) string {
	switch role {
	case "admin":
		return "Admin"
	case "moderator":
		return "Moderator"
	case "premium":
		return "Premium"
	case "artist":
		return "Artist"
	case "guest":
		return "Guest"
	default:
		return "User"
	}
}