# natcmp.rb
#
# Natural order comparison of two strings
# e.g. "my_prog_v1.1.0" < "my_prog_v1.2.0" < "my_prog_v1.10.0"
# which does not follow alphabetically
#
# Based on Martin Pool's "Natural Order String Comparison" originally written in C
# http://sourcefrog.net/projects/natsort/
#
# This implementation is Copyright (C) 2003 by Alan Davies
# <cs96and_AT_yahoo_DOT_co_DOT_uk>
#
# This software is provided 'as-is', without any express or implied
# warranty.  In no event will the authors be held liable for any damages
# arising from the use of this software.
#
# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:
#
# 1. The origin of this software must not be misrepresented; you must not
#    claim that you wrote the original software. If you use this software
#    in a product, an acknowledgment in the product documentation would be
#    appreciated but is not required.
# 2. Altered source versions must be plainly marked as such, and must not be
#    misrepresented as being the original software.
# 3. This notice may not be removed or altered from any source distribution.

class String

  # 'Natural order' comparison of two strings
  def String.natcmp(str1, str2, caseInsensitive=false)
    str1, str2 = str1.dup, str2.dup
    compareExpression = /^(\D*)(\d*)(.*)$/

    if caseInsensitive
      str1.downcase!
      str2.downcase!
    end

    # Remove all whitespace
    str1.gsub!(/\s*/, '')
    str2.gsub!(/\s*/, '')

    while (str1.length > 0) or (str2.length > 0) do
      # Extract non-digits, digits and rest of string
      str1 =~ compareExpression
      chars1, num1, str1 = $1.dup, $2.dup, $3.dup

      str2 =~ compareExpression
      chars2, num2, str2 = $1.dup, $2.dup, $3.dup

      # Compare the non-digits
      case (chars1 <=> chars2)
        when 0 # Non-digits are the same, compare the digits...
          # If either number begins with a zero, then compare alphabetically,
          # otherwise compare numerically
          if (num1[0] != 48) and (num2[0] != 48)
            num1, num2 = num1.to_i, num2.to_i
          end

          case (num1 <=> num2)
            when -1 then return -1
            when 1 then return 1
          end
        when -1 then return -1
        when 1 then return 1
      end # case

    end # while

    # Strings are naturally equal
    return 0
  end

end # class String