From: "Ara.T.Howard" <ahoward@...>
Date: 2004-04-02T03:14:27+09:00
Subject: Re: How to get internal state of DateTime in seconds

On Thu, 1 Apr 2004, Charles Comstock wrote:

> > iff
> >   - your times are a common format
> >   - your times are within the ranges allowable by Time
> > 
> > both of which appear to be true why not simply parse the time yourself?  this
> > is plenty clean, especially if it's in instance method of a LogEntry class or
> > something:
> > 
> > 
> > file: logtm.rb
> > 
> > def logtm s
> > #{{{
> >   pat = 
> >     %r|^\s*(\d\d)/(\w\w\w)/(\d\d\d\d):(\d\d):(\d\d):(\d\d)\s+\+(\d\d)(\d\d)\s*$|io
> > 
> >   s = s.to_s
> >   m = pat.match s
> >   raise ArgumentError, "<#{ s.inspect }>" unless m
> > 
> >   parts = m.to_a
> >   raise ArgumentError, "<#{ s.inspect }>" unless parts.size == 9  
> > 
> >   parts.shift
> >   day, month, year, hour, min, sec, zhour, zmin = parts
> > 
> >   months = %w(jan feb mar apr may jun jul aug sep oct nov dec)
> >   i = months.index month.downcase
> >   raise ArgumentError, "<#{ s.inspect }>" unless i
> >   month = i + 1
> > 
> >   day, month, year, hour, min, sec, zhour, zmin =
> >     [day, month, year, hour, min, sec, zhour, zmin].map{|x| x.to_i}
> > 
> >   utc = Time.utc year, month, day, hour, min, sec, usec = 0
> > 
> >   t = utc + ((zhour * 60 * 60) + (zmin * 60)) 
> > #}}}
> > end
> > 
> > str1 = '20/Nov/2003:08:08:09 +0200'
> > str2 = '20/Nov/2003:08:04:09 +0200'
> > t1   = logtm str1
> > t2   = logtm str2
> > 
> > #what is difference in minutes between these 2 times?
> > p((t1 - t2).abs / 60.0) # => 4.0
> > 
> > 
> > -a
> 
> Umm I don't understand how this relates, I can construct Time objects from
> strings just fine (parsedate), I want a library to take the time difference
> in seconds from two Time or Date objects, and format output of that into
> something meaningful, ie %H:%M:%S would result in "00:04:00" for your
> example difference.  But it should scale all the way up to differences in
> Months/Years.  It seems like a perfectly useful library, and I was suprised
> it hadn't been written.  Yes it's just division up to months, and then
> months cares what the actual start/end times were, but still it seems like a
> useful object.  Seconds is all fine and good when your just recording short
> ranges, but for longer...

i think i would be suprisingly difficult to do this for anything other than
seconds when you consider leap years/seconds and diffs which span multiple
leap years.

consider

    span = TimeSpan.new t0, t1

    span.years # => 3

    t0 + (span.years * YEAR_SEC) # but what if one of those years was a leap year!

ok so you could

    span = TimeSpan.new t0, t1

    t2 = span.add_years t0

but this will really just use seconds under the hood right?

the hard part is - how t you represent an 'absolute' time span in anything
other than one unit (seconds is only one) AND give a methods for breaking this
unit up into chunks (days, years) such that the chunks retain their leapness?
i suppose you could

  class TimeSpan
    class Year
    end
    class Day
    end
  end


and extend Time/Data to use those... but surely this is far more error prone
than using utc and seconds?

-a
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