// 1. バリデーション責任
class UserValidator {
    validate(userData) {
        const errors = [];
        
        if (!userData.email || !this.isValidEmail(userData.email)) {
            errors.push('Invalid email format');
        }
        
        if (!userData.password || userData.password.length < 8) {
            errors.push('Password must be at least 8 characters');
        }
        
        if (userData.age && userData.age < 18) {
            errors.push('Must be 18 or older');
        }
        
        if (errors.length > 0) {
            throw new ValidationError(errors);
        }
    }
    
    private isValidEmail(email) {
        return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
    }
}

// 2. パスワード処理責任
class PasswordService {
    async hash(password) {
        const salt = crypto.randomBytes(16).toString('hex');
        const hash = crypto.pbkdf2Sync(password, salt, 1000, 64, 'sha512').toString('hex');
        return { hash, salt };
    }
    
    async verify(password, hash, salt) {
        const verifyHash = crypto.pbkdf2Sync(password, salt, 1000, 64, 'sha512').toString('hex');
        return hash === verifyHash;
    }
}

// 3. ユーザーエンティティ
class User {
    constructor(data) {
        this.id = data.id || this.generateId();
        this.email = data.email.toLowerCase();
        this.passwordHash = data.passwordHash;
        this.passwordSalt = data.passwordSalt;
        this.age = data.age;
        this.createdAt = data.createdAt || new Date();
    }
    
    private generateId() {
        return Date.now().toString() + Math.random().toString(36).substr(2, 9);
    }
}

// 4. リポジトリ責任
interface UserRepository {
    save(user: User): Promise;
    findByEmail(email: string): Promise;
}

class MySQLUserRepository implements UserRepository {
    constructor(private connectionPool) {}
    
    async save(user) {
        await this.connectionPool.execute(
            'INSERT INTO users (id, email, password_hash, password_salt, age, created_at) VALUES (?, ?, ?, ?, ?, ?)',
            [user.id, user.email, user.passwordHash, user.passwordSalt, user.age, user.createdAt]
        );
    }
    
    async findByEmail(email) {
        const [rows] = await this.connectionPool.execute(
            'SELECT * FROM users WHERE email = ?',
            [email]
        );
        return rows.length > 0 ? new User(rows[0]) : null;
    }
}

// 5. 通知責任
interface NotificationService {
    sendWelcomeEmail(user: User): Promise;
}

class EmailNotificationService implements NotificationService {
    constructor(private emailTransporter) {}
    
    async sendWelcomeEmail(user) {
        await this.emailTransporter.sendMail({
            from: 'noreply@myapp.com',
            to: user.email,
            subject: 'Welcome to MyApp!',
            html: `
Welcome ${user.email}!
Thank you for joining us.
`
        });
    }
}

// 6. 統計責任
class UserStatisticsService {
    constructor(private statsRepository) {}
    
    async incrementUserCount() {
        const stats = await this.statsRepository.get();
        stats.totalUsers++;
        stats.lastSignup = new Date();
        await this.statsRepository.save(stats);
    }
}

// 7. ユースケース（調整役）
class CreateUserUseCase {
    constructor(
        private validator: UserValidator,
        private passwordService: PasswordService,
        private userRepository: UserRepository,
        private notificationService: NotificationService,
        private statisticsService: UserStatisticsService,
        private logger: Logger
    ) {}
    
    async execute(userData) {
        // 検証
        this.validator.validate(userData);
        
        // 重複チェック
        const existingUser = await this.userRepository.findByEmail(userData.email);
        if (existingUser) {
            throw new Error('Email already registered');
        }
        
        // パスワードハッシュ化
        const { hash, salt } = await this.passwordService.hash(userData.password);
        
        // ユーザー作成
        const user = new User({
            email: userData.email,
            passwordHash: hash,
            passwordSalt: salt,
            age: userData.age
        });
        
        // 保存
        await this.userRepository.save(user);
        
        // 通知（エラーがあっても処理は続行）
        try {
            await this.notificationService.sendWelcomeEmail(user);
        } catch (error) {
            this.logger.error('Failed to send welcome email', error);
        }
        
        // 統計更新
        await this.statisticsService.incrementUserCount();
        
        // ログ
        this.logger.info(`New user registered: ${user.email}`);
        
        return user;
    }
}