defimpl Enumerable, for: AgentMap do
  import AgentMap

  def count(%AgentMap{link: mag}) do
    {:ok, GenServer.call(mag, :count)}
  end

  def member?(mag, {key, value}) do
    case fetch(mag, key) do
      {:ok, ^value} -> {:ok, true}
      _ -> {:ok, false}
    end
  end

  def slice(mag) do
    map = take(mag, keys(mag))
    {:ok, map_size(map), &Enumerable.List.slice(:maps.to_list(map), &1, &2)}
  end

  def reduce(mag, acc, fun) do
    map = take(mag, keys(mag))
    reduce_list(:maps.to_list(map), acc, fun)
  end

  defp reduce_list(_, {:halt, acc}, _fun), do: {:halted, acc}
  defp reduce_list([], {:cont, acc}, _fun), do: {:done, acc}

  defp reduce_list([h | t], {:cont, acc}, fun) do
    reduce_list(t, fun.(h, acc), fun)
  end

  defp reduce_list(list, {:suspend, acc}, fun) do
    {:suspended, acc, &reduce_list(list, &1, fun)}
  end
end