How to parse a text file with pattern matching, and converted to a nested list

record_file.exs

# https://elixirforum.com/t/newbie-needs-help-parsing-a-file/1762
defmodule RecordFile do
  def read(file) do
    {:ok, data} = File.read(file)
    
    data
    |> String.split("\n")
    |> filter
  end

  def filter(list),
    do: filter(list, [], [], false)

  defp filter(["~~BOM" | tail], result, acc, _record?),
    do: filter(tail, result, acc, true)
  defp filter(["~~" | tail], result, acc, _record?),
    do: filter(tail, [Enum.reverse(acc) | result], [], false)
  defp filter([head | tail], result, acc, true),
    do: filter(tail, result, [head | acc], true)
  defp filter([_head | tail], result, acc, false),
    do: filter(tail, result, acc, false)
  defp filter([], result, _acc, _record?),
    do: Enum.reverse(result)
end


# records.txt: (remove the #)
# rec1
# rec2
# ~~BOM
# PVDocMgmt1.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572
# PVDocMgmt2.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572
# ~~
# rec3
# rec4
# ~~BOM
# PVDocMgmt3.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572
# PVDocMgmt4.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572
# ~~
# rec5
# rec6

IO.inspect RecordFile.read("records.txt")

# OUTPUT
# $ elixir record_file.exs 
# [["PVDocMgmt1.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572",
#   "PVDocMgmt2.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572"],
#  ["PVDocMgmt3.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572",
#   "PVDocMgmt4.dll -- DateTime = 20160906082015;md5=MD5=2e59ba41a50a5ff2ab530519281bc572"]]