WC on counters

wc-counters.ex

defmodule Wc do
  @prehandle 42
  @sink @prehandle + 1
  @chunk 1_000_000

  @type acc_counters :: 0 | 1

  @spec counters(binary) :: acc()
  def counters(file) do
    cs = :counters.new(3, [:write_concurrency])

    file
    |> File.stream!([], @chunk)
    |> Flow.from_enumerable()
    |> Flow.partition()
    |> Flow.reduce(fn -> 1 end, &parse_counters(&1, &2, cs))
    |> Flow.run()

    %{bc: :counters.get(cs, 1), lc: :counters.get(cs, 3), wc: :counters.get(cs, 2)}
  end

  defmacrop ns!(0, ns), do: ns
  defmacrop ns!(_, _), do: 1

  defmacrop acc_counters!(cs, bc, ns, lc) do
    quote do
      :counters.add(unquote(cs), 1, unquote(bc))
      :counters.add(unquote(cs), 2, unquote(ns))
      :counters.add(unquote(cs), 3, unquote(lc))
      ns!(unquote(bc), unquote(ns))
    end
  end

  @spec parse_counters(<<_::_*8>>, acc_counters(), :counters.counters_ref()) :: acc_counters()

  Enum.each(0..@prehandle, fn i ->
    def parse_counters(
          <<_::binary-size(unquote(i)), ?\n, rest::binary>>, ns, cs
        ),
        do: parse_counters(rest, acc_counters!(cs, 1 + unquote(i), ns, 1), cs)

    def parse_counters(
          <<_::binary-size(unquote(i)), ?\s, rest::binary>>, ns, cs
        ),
        do: parse_counters(rest, acc_counters!(cs, 1 + unquote(i), ns, 0), cs)
  end)

  def parse_counters(<<_::binary-size(@sink), rest::binary>>, _acc, cs),
    do: parse_counters(rest, acc_counters!(cs, @sink, 1, 0), cs)

  Enum.each(@prehandle..0, fn i ->
    def parse_counters(<<_::binary-size(unquote(i))>>, _acc, cs),
      do: acc_counters!(cs, 1 + unquote(i), 1, 0)
  end)
end