defmodule CR do
  @moduledoc """
  A little program to read a simple CSV file and summ
  all of the numbers along the row.  Anything non-numeric
  is treated as 0. The file name is given on the command line

  Usage: elixir commread.ex filename

  author:  gtowell
  created: August 2022
  """

  @doc """
  A small function to process each line in the CSV file.
  Just sums up everything that can be parsed to an integer
  The return value from this function is nil and is unused as this
  function is run for its side effect
  """
  def do_line(line) do
    String.split(line, ",")
    |> Enum.reduce(0, fn (value, acc) ->
      # Integer.parse returns :error on failure
      # Use case command to handle expected and error
      # note that _ will match to anything so :error matches
      case Integer.parse(value) do
        {ival, _rr} -> acc+ival
        _ -> acc
        end
      end)
    |> IO.puts
  end

  @doc """
  read a file given on the command line
  Pass that file off, after first splitting it into a list of
  the lines in the file, to a handler
  If there is more than one argument given on the command line
  all but the first is ignored. If none given, just a usage message
  """
  def main do
    # Use case command to handle user not providing a file
    # name on the command line.   In that case the list from
    # argv has only one item so it does not match [h|_]
    # _ matches anything so when no command line param
    # print out a usage message
    case System.argv() do
      [h|_] -> {:ok, txt} = File.read(h)
        String.split(txt, "\n")
        |> Enum.each(fn v -> do_line(v) end)
      _ -> IO.puts "Usage: elixir commread.ex filename"
    end
  end

  def main2() do
    IO.inspect(System.argv())
  end
end

CR.main2
#CR.main