defmodule MessageServer.RemoteHandler do
  require Logger

  @spec handle_remote_message(map()) :: :ok | {:error, String.t()}
  def handle_remote_message(%{from: from, to: to, message: message}) do
    with {:ok, to_server} <- extract_server_id(to),
         :ok <- validate_recipient_ownership(to_server) do
      MessageServer.Storage.append_message(to, from, message)
    end
  end

  @spec extract_server_id(String.t()) :: {:ok, String.t()} | {:error, String.t()}
  defp extract_server_id(user_id) do
    case String.split(user_id, "-", parts: 2) do
      [server_id, _user_part] -> {:ok, server_id}
      _ -> {:error, "Invalid user ID format: #{user_id}"}
    end
  end

  @spec validate_recipient_ownership(String.t()) :: :ok | {:error, String.t()}
  defp validate_recipient_ownership(recipient_server) do
    local_server = MessageServer.ServerRegistry.get_server_id()

    if recipient_server == local_server do
      :ok
    else
      {:error, "Cannot deliver messages to users from other servers"}
    end
  end
end