multi.ex

defmodule Example.Utils.Multi do

  @doc """
  Intertwine multi calls with callbacks to a function to report progress information.
  """
  def add_progress_calls(multi, fun) do
    operations = multi.operations |> Enum.with_index()
    size = Enum.count(operations)
    new_operations =
      Enum.reduce(operations, [], fn({op, index}, all) ->
        percentage = (size - index) / size
        progress = {["progress", index], {:run, fn(_) -> {:ok, fun.(percentage)} end}}
        [progress, op | all]
      end)
      |> Enum.reverse()

    %Ecto.Multi{operations: new_operations, names: MapSet.new(new_operations |> Enum.into(%{} |> Map.keys()))}
  end

end