---

class User private constructor(
    val username: String,
    val email: String,
    val age: Int
) {
    // companion object — «статика» по-котлиновски
    companion object {
        const val MIN_AGE = 0
        const val MAX_AGE = 150

        fun createGuest(): User = User("guest", "guest@example.com", 0)

        fun fromMap(map: Map<String, String>): User? {
            val username = map["username"] ?: return null
            val email = map["email"] ?: return null
            val age = map["age"]?.toIntOrNull() ?: return null

            return if (age in MIN_AGE..MAX_AGE) User(username, email, age) else null
        }
    }

    override fun toString(): String =
        "User(username='$username', email='$email', age=$age)"
}

fun main() {
    val guest = User.createGuest()

    // корректная карта
    val alex = User.fromMap(
        mapOf(
            "username" to "alex",
            "email" to "alex@mail.ru",
            "age" to "25"
        )
    )

    // некорректная карта — без email, должно быть null
    val invalid = User.fromMap(
        mapOf(
            "username" to "bob",
            "age" to "30"
        )
    )

    println(guest)
    println(alex)
    println(invalid)   // null
}