kotlin_repository_cache2.kt

class UserRepository2(
    userDao: UserDao
) {
  private val userDaoWithCache = Cache2(userDao::getUser)
  private val userDao2WithCache = Cache2(userDao::getUser2)

  fun getUser(id: Int, name: String): Single<User> =
      userDaoWithCache(id, name)

  fun getUser2(id: Int, name: String, password: String): Single<User> =
      userDao2WithCache(id, name, password)
}

class UserDao {
  fun getUser(id: Int, name: String): Single<User> {
    return Single.just(User(id, name))
        .delay(500, TimeUnit.MILLISECONDS)
  }

  fun getUser2(id: Int, name: String, password: String): Single<User> {
    if (password.isEmpty()) return Single.error(Exception())
    return Single.just(User(id, name))
        .delay(500, TimeUnit.MILLISECONDS)
  }
}

data class User(val id: Int, val name: String)

class Cache2<R>(
    private val invoker: Function<Single<R>>
) {
  private val cache = HashMap<Int, R>()

  operator fun invoke(vararg args: Any): Single<R> {
    val key = hashCode(args)
    cache[key]?.let {
      return Single.just(it)
    }
    return ((invoker as? Function1<Any, Single<R>>)?.invoke(args[0])
        ?: (invoker as? Function2<Any, Any, Single<R>>)?.invoke(args[0], args[1])
        ?: (invoker as? Function3<Any, Any, Any, Single<R>>)?.invoke(args[0], args[1], args[2])
        ?: throw IllegalArgumentException("no much Function type")
        ).doOnSuccess { cache[key] = it }
  }

  // todo it's wrong hashcode
  private fun hashCode(args: Array<out Any>): Int = args.sumBy { it.hashCode() }
}