package auth

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

	"github.com/golang-jwt/jwt/v5"
	"gorm.io/gorm"

	"onixbyte.com/pipely/internal/database"
	"onixbyte.com/pipely/internal/model"
)

var (
	ErrInvalidCredentials = errors.New("invalid username or password")
	ErrUserExists         = errors.New("username already exists")
)

type Service struct {
	db     *gorm.DB
	secret []byte
	expiry time.Duration
}

func NewService(db *gorm.DB, secret []byte, expiryHrs int) *Service {
	return &Service{
		db:     db,
		secret: secret,
		expiry: time.Duration(expiryHrs) * time.Hour,
	}
}

func (s *Service) Login(username, password string) (*model.LoginResponse, error) {
	user, err := database.GetAdminUserByUsername(s.db, username)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrInvalidCredentials
		}
		return nil, err
	}

	hash := hashPassword(password)
	if subtle.ConstantTimeCompare([]byte(hash), []byte(user.PasswordHash)) != 1 {
		return nil, ErrInvalidCredentials
	}

	token, expiresAt, err := s.generateToken(user)
	if err != nil {
		return nil, err
	}

	return &model.LoginResponse{
		Token:     token,
		ExpiresAt: expiresAt,
	}, nil
}

func (s *Service) CreateInitialAdmin(username, password string) error {
	_, err := database.GetAdminUserByUsername(s.db, username)
	if err == nil {
		return nil // admin already exists
	}

	user := &model.AdminUser{
		Username:     username,
		PasswordHash: hashPassword(password),
		Role:         "admin",
	}
	return s.db.Transaction(func(tx *gorm.DB) error {
		return database.CreateAdminUser(tx, user)
	})
}

func (s *Service) ValidateToken(tokenString string) (*model.AdminUser, error) {
	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, errors.New("unexpected signing method")
		}
		return s.secret, nil
	})
	if err != nil {
		return nil, err
	}

	claims, ok := token.Claims.(jwt.MapClaims)
	if !ok || !token.Valid {
		return nil, errors.New("invalid token")
	}

	username, _ := claims["sub"].(string)
	if username == "" {
		return nil, errors.New("invalid token subject")
	}

	return database.GetAdminUserByUsername(s.db, username)
}

func (s *Service) generateToken(user *model.AdminUser) (string, int64, error) {
	expiresAt := time.Now().Add(s.expiry)
	claims := jwt.MapClaims{
		"sub":  user.Username,
		"role": user.Role,
		"iat":  time.Now().Unix(),
		"exp":  expiresAt.Unix(),
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	tokenStr, err := token.SignedString(s.secret)
	if err != nil {
		return "", 0, err
	}

	return tokenStr, expiresAt.Unix(), nil
}

func hashPassword(password string) string {
	h := sha256.Sum256([]byte(password))
	return hex.EncodeToString(h[:])
}

func (s *Service) ListUsers() ([]model.AdminUser, error) {
	return database.ListAdminUsers(s.db)
}

func (s *Service) CreateUser(username, password, role string) (*model.AdminUser, error) {
	_, err := database.GetAdminUserByUsername(s.db, username)
	if err == nil {
		return nil, ErrUserExists
	}

	if role == "" {
		role = "admin"
	}

	user := &model.AdminUser{
		Username:     username,
		PasswordHash: hashPassword(password),
		Role:         role,
	}
	if err := database.CreateAdminUser(s.db, user); err != nil {
		return nil, err
	}
	return user, nil
}

func (s *Service) DeleteUser(id int64) error {
	return database.DeleteAdminUser(s.db, id)
}

func (s *Service) ChangePassword(id int64, newPassword string) error {
	return database.UpdateAdminPassword(s.db, id, hashPassword(newPassword))
}