vnode.ex

  def is_empty(state) do
    result = :queue.is_empty(state.queue)
    Logger.debug "#{inspect __MODULE__}: Empty? #{inspect result}."
    {result, state}
  end

  def delete(state) do
    Logger.debug "#{inspect __MODULE__}: Deleting #{inspect state}."
    {:ok, state}
  end

  def handoff_starting(target_node, state) do
    Logger.debug "#{inspect __MODULE__}: Handoff to #{inspect target_node} starting."
    {true, state}
  end

  def handoff_cancelled(state) do
    Logger.debug "#{inspect __MODULE__}: Cancelling handoff #{inspect state}."
    {:ok, state}
  end

  def handle_handoff_data(bin, state) do
    Logger.debug "#{inspect __MODULE__}: Handling handoff item #{inspect bin} - #{inspect state}"
    {"queue", queue} = :erlang.binary_to_term(bin)
    {:reply, :ok, %{state | queue: queue}}
  end

  @doc """
  The `visit_fun` is `riak_core_handoff_sender:visit_item/3`. It is going to do all of the hard work of taking your
  serialized data and pushing it over the wire to the remote node.

  `acc0` here is the internal state of the handoff. `riak_core_handoff_sender:visit_item/3` returns an updated handoff
  state, so you should use that in your own fold over vnode data elements.
  """
  def handle_handoff_command(riak_core_fold_req_v2(foldfun: visit_fun, acc0: acc0), sender, state) do
    Logger.debug "#{inspect __MODULE__}: Handling handoff command #{inspect acc0} - #{inspect sender} - #{inspect state}"
    work = visit_fun.(:any, {"queue", state.queue}, acc0)
    {:reply, work, state}
  end

  def encode_handoff_item(k, {"queue", queue} = data) do
    Logger.debug "#{inspect __MODULE__}: Encoding handoff item #{inspect k} #{inspect queue}."
    :erlang.term_to_binary(data)
  end