Take the delta of two maps

delta_map.ex

  @spec delta_map(path(), map(), map()) :: [delta()]
  def delta_map(path, a, b) do
    a_keys = MapSet.new(Map.keys(a))
    b_keys = MapSet.new(Map.keys(b))
    common = MapSet.intersection(a_keys, b_keys)
    a_only = a_keys |> MapSet.difference(common)
    b_only = b_keys |> MapSet.difference(common)

    Enum.flat_map(common, fn key -> delta([key | path], a[key], b[key]) end) ++
      Enum.flat_map(a_only, fn key -> [{[key | path], {:delete, a[key]}}] end) ++
      Enum.flat_map(b_only, fn key -> [{[key | path], {:add, b[key]}}] end)
  end