#!/usr/bin/ruby -w

require 'algorithm/diff'

module Diff
	class Hunk
		attr_reader :type, :content

		def initialize(type, content)
			@type = type
			@content = content
		end
	end

	def Diff.word_diff(s1, s2)
		words = [s1, s2].collect { |str| 
			str.split(/\b(?=\w)/xm)
		}
		differences = diff(words[0], words[1])
		
		# Same string
		return [ Hunk.new(:both, s1) ] if differences.length == 0
	
		hunks = []
		# Adding lengths that are the same involves a similar operation 
		# three times.  Using a proc allows knowledge of private
		# data without having to make this a class
		push_identical = proc { |beginning, ending|
			return unless ending - beginning > 1
			hunks.push(Hunk.new(:both, words[0][beginning..ending-1].join))
		}
	
		# Leading identical stuff
		push_identical.call(0, differences[0][1])

		differences.each_with_index { |d, i|
			hunks.push(Hunk.new(d[0] == :+ ? :right : :left, d[2].join))
			push_identical.call(differences[i][1], differences[i + 1][1]) unless differences[i + 1].nil?
		}

		# Trailing identical stuff
		push_identical.call(differences[-1][1] + 1, words[0].length)

		return hunks
	end
end