pop3mail

defmodule Pop3mail.DateConverter do

   @moduledoc "Date conversions and date utilities"

   @doc "add zero's at left side of the number"
   def zero_pad(number, len \\ 2) do
     String.rjust(to_string(number), len, ?0)
   end

   @doc """

   Convert date from email header to a standard date format: YYYYMMDD_HHMMSS



   `datestr` - must be conform RFC 2822 date format

   """
   def convert_date(date_str) do
     # Example of correctly formatted date: Tue, 14 Oct 2014 19:59:31 +0200

     # Sometimes the day of the week is missing in the date. Fix that:

     # if date starts with digit, add the day first. We don't care which day it is, just add ???

     date_str =
        case date_str =~ ~r/^\s?\d/ do
           true  -> "???, " <> date_str
           false -> date_str
        end
     # httpd_util requires that single digit days have a leading zero. This is not always the case.

     day_and_date = date_str
                    |> String.slice(5..-1)
                    |> String.lstrip
     # add leading zero

     date_str =
       case day_and_date =~ ~r/^\d\s/ do
         true  -> String.slice(date_str, 0..4) <> "0" <> day_and_date
         false -> date_str
       end
     date_char_list = to_char_list(date_str)
     {{year, month, day}, {hour, minutes, seconds}} = :httpd_util.convert_request_date(date_char_list)
     zero_pad(year, 4) <> zero_pad(month) <> zero_pad(day) <> "_" <> zero_pad(hour) <> zero_pad(minutes) <> zero_pad(seconds)
   end

end