From: Josef 'Jupp' SCHUGT <jupp@...>
Date: 2004-01-21T09:27:56+09:00
Subject: Parsing periods of time: Code and questions

Hi!

I am presently working on a new version of my feed aggregator
'rubric'. This time I am focussing on security issues so among other
changes the config file will no longer be a Ruby script. For parsing
a string that defines a period of time I wrote the following little
routine (GPL applies, long lines but still < 80 characters):

def to_sec(argument)
  return argument if argument.class < Integer
  if argument.class == String
    case argument
      when /^(.*?)[+,](.*)$/                     then to_sec($1) + to_sec($2)
      when /^\s*([0-9_]+)\s*\*(.+)$/             then $1.to_i * to_sec($2)
      when /^\s*[0-9_]+\s*(s(ec(ond)?s?)?)?\s*$/ then argument.to_i
      when /^\s*([0-9_]+)\s*m(in(ute)?s?)?\s*$/  then $1.to_i *      60
      when /^\s*([0-9_]+)\s*h(ours?)?\s*$/       then $1.to_i *    3600
      when /^\s*([0-9_]+)\s*d(ays?)?\s*$/        then $1.to_i *   86400
      when /^\s*([0-9_]+)\s*w(eeks?)?\s*$/       then $1.to_i *  604800
      when /^\s*([0-9_]+)\s*months?\s*$/         then $1.to_i * 2419200
      else                                            0
    end
  end
end

Two questions arise:

1. Should one require integral values or would it be better to allow
   the use of decimal numbers?
2. If decimal numbers are allowed would it be a good idea to allow
   the use of exponential notation?

What the above code allows you to do: You can specify

  n seconds as: n, n s, n sec, n secs, n second, n seconds
  n minutes as:    n m, n min, n mins, n minute, n minutes
  n hours   as:    n h,                n hour,   n hours
  n weeks   as:    n w,                n week,   n weeks
  n months  as:                        n month   n months

where a month has 28 days. You can use multiplications so that the
following values are identical:

  * 1 month
  * 4 weeks
  * 4 * 24 hours
  * 4 * 24 * 60 minutes
  * 4 * 24 * 60 * 60 seconds

You can also use additions which can be written in a mathematical way
using a '+' sign or as you read (using colons) so that the following
values are identical:

  * 2 month + 3 weeks + 5 days + 7 hours + 11 minutes + 13 seconds
  * 2 month, 3 weeks, 5 days, 7 hours, 11 minutes, 13 seconds
  * 2 * 4 weeks, 3 * 7 days, 5 * 24 hours, 7 * 60 minutes,
    11 * 60 seconds, 13 seconds

Even '2 * 4 * 7 * 24 * 60 * 60 s, 3 * 7 * 24 * 60 * 60 s,
5 * 24 * 60 * 60 s, 7 * 60 * 60 s, 11 * 60 s, 13 s' is possible
(although it is not recommended :-).

Josef 'Jupp' SCHUGT
-- 
http://oss.erdfunkstelle.de/ruby/    -     German comp.lang.ruby-FAQ
http://rubyforge.org/users/jupp/     -     Ruby projects at Rubyforge
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