From: Phrogz <gavin@...>
Date: 2007-04-06T23:25:09+09:00
Subject: Re: Calculating Business Hours Left

On Apr 6, 8:13 am, "Keith Fahlgren" <k...@audiobeta.com> wrote:
> Hmm... no idea if this works, but it might be a start:

That feels like it might be good, thanks! I'll have to investigate
more. It  certainly looks cleaner than what I came up with:

class Time
  def at( hrs, mins=0 )
    self.class.parse strftime("%Y-%b-%d #{hrs}:#{mins}" )
  end
end

# Fails for tasks one year or farther in the future
def work_hours_until( due_time, work_starts_at=9, work_ends_at=17 )
  start_time = [
    Time.now,
    Time.parse( "#{work_starts_at}:00" )
  ].max
  end_time = [
    due_time,
    due_time.at( work_ends_at )
  ].min

  weekdays = 1..5
  one_hour = 3600.0
  one_day  = one_hour * 24

  if start_time.yday == end_time.yday
    if weekdays.include?( start_time.wday )
      ( end_time - start_time ) / one_hour
    else
      0
    end
  else
    business_hours = work_ends_at - work_starts_at

    # Handle partial hours on the first day
    hours = ( start_time.at( work_ends_at ) - start_time ) / one_hour

    t = start_time + one_day
    until t.yday == due_time.yday
      hours += business_hours if weekdays.include?( t.wday )
      t += one_day
    end

    # Handle partial hours on the last day
    if weekdays.include?( t.wday )
      hours += ( end_time - end_time.at( work_starts_at ) ) / one_hour
    end

    hours
  end

end