Format date ranges according to the Wikipedia styleguide (http://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Dates_and_numbers#Ranges)

gistfile1.rb

def format_date_range(from, to)
  to = from if to.nil?
  return '' if from.nil? && to.nil?
  from, to = to, from if to < from

  if from == to
    from.strftime('%B %e, %Y')
  elsif from.year == to.year && from.month == to.month &&
    from.beginning_of_month == from && to.end_of_month == to
    from.strftime('%B %Y')
  elsif from.year == to.year &&
    from.beginning_of_month == from && to.end_of_month == to
    "#{from.strftime('%B')}–#{to.strftime('%B %Y')}"
  elsif from.beginning_of_month == from && to.end_of_month == to
    "#{from.strftime('%B %Y')} – #{to.strftime('%B %Y')}"
  elsif from.year == to.year && from.month == to.month
    "#{from.strftime('%B %e')}–#{to.strftime('%e, %Y')}"
  elsif from.year == to.year
    "#{from.strftime('%B %e')} – #{to.strftime('%B %e, %Y')}"
  else
    "#{from.strftime('%B %e, %Y')} – #{to.strftime('%B %e, %Y')}"
  end.gsub(/\s{2,}/,' ')
end

gistfile2.rb

# date ranges, including year threshold and full month
assert_equal "April 2–17, 2014",
  format_date_range(Date.new(2014,4,2),Date.new(2014,4,17))
assert_equal "December 13, 2013 – January 4, 2014",
  format_date_range(Date.new(2013,12,13),Date.new(2014,1,4))
assert_equal "May–June 2014",
  format_date_range(Date.new(2014,5,1),Date.new(2014,6,30))
assert_equal "October 2013 – June 2014",
  format_date_range(Date.new(2013,10,1),Date.new(2014,6,30))
assert_equal "April 2014",
  format_date_range(Date.new(2014,4,1),Date.new(2014,4,30))

# dates in reverse order
assert_equal "April 2–17, 2014",
  format_date_range(Date.new(2014,4,17),Date.new(2014,4,2))
assert_equal "December 13, 2013 – January 4, 2014",
  format_date_range(Date.new(2014,1,4),Date.new(2013,12,13))
assert_equal "April 2014",
  format_date_range(Date.new(2014,4,30),Date.new(2014,4,1))

# same day
assert_equal "April 4, 2014",
  format_date_range(Date.new(2014,4,4),Date.new(2014,4,4)

Note, this doesn't do year–year, but that could be easily added.