sensible_sort.rb

# Based on Dave Koelle's Alphanum algorithm
# Rik Hemsley, 2007
# WegoWise Inc., 2013
# See also http://rikkus.info/arch/sensible_sort.rb

#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
#

module Enumerable

  def sensible_sort
    sort { |a, b| grouped_compare(a, b) }
  end

  def sensible_sort!
    sort! { |a, b| grouped_compare(a, b) }
  end

  def sensible_sort_by(&block)
    sort { |a, b| grouped_compare(block.call(a), block.call(b)) }
  end

  def sensible_sort_by!(&block)
    sort! { |a, b| grouped_compare(block.call(a), block.call(b)) }
  end

  private

  def grouped_compare(a, b)
    loop {
      a_chunk, a = extract_alpha_or_number_group(a)
      b_chunk, b = extract_alpha_or_number_group(b)

      # Don't try to compare numeric to string if one of group is not numeric
      unless [a_chunk, b_chunk].all? {|chunk| chunk.is_a?(Numeric) }
        a_chunk, b_chunk = [a_chunk, b_chunk].map(&:to_s)
      end

      ret = a_chunk <=> b_chunk

      return -1 if a_chunk == ''
      return ret if ret != 0
    }
  end

  def extract_alpha_or_number_group(item)
    matchdata = /([A-Za-z]+|[\d]+)/.match(item)
    if matchdata.nil?
      ["", ""]
    else
      chunk = matchdata[0]
      chunk = chunk.to_i if chunk =~ /\A\d+\Z/
      [chunk, item = item[matchdata.offset(0)[1] .. -1]]
    end
  end

end