From: Kev Jackson <kevin.jackson@...>
Date: 2005-10-28T19:15:09+09:00
Subject: failed GDiff attempt was [Re: Ruby Quiz for building up Ruby?]

Well I've got to dash off early today, but here's something I've hacked 
together (very rough)

I'm sure there are many better ways of doing this - indeed my algorithm 
is very naive, it doesn't scan for matches in an efficient way (just 
barely scans :)
The approach I was going for was to have a GDiffFile class, and then 
create various GDiff command objects and pump them into the file.

At the moment it will spit out a semi-compliant gdiff file, but it's 
horrendously bloated, and I couldn't find a nice way to quote strings as 
in the example on

http://www.w3.org/TR/NOTE-gdiff-19970901

Kev

GDiff composer (just bytes, not longs etc), not in class, just hacking 
at the script really

gdiff.rb
require 'lib/gdiff_copy'
require 'lib/gdiff_data'
require 'lib/gdiff_file'

diff_file = GDiff::GDiffFile.new("d:\\ruby_projects\\gdiff\\test")
diff_file.put_header

# get data into arrays
old = IO.read("d:\\ruby_projects\\gdiff\\gdiff.rb").scan(/./)
new = IO.read("d:\\ruby_projects\\gdiff\\gdiff_new.rb").scan(/./)

# dumb scan comparing single chars, should make it compare matching 
sequences
pos =0
old.each do |oldb|
diff_file.put_cmd_and_data(GDiff::GDiffCopy.new(pos, 1)) if new[pos] == oldb
diff_file.put_cmd_and_data(GDiff::GDiffData.new(1,new[pos])) if new[pos] 
!= oldb
pos +=1
end
diff_file.put_trailer
diff_file.write_diff


lib/gdiff_cmd.rb

module GDiff
  class GDiffCmd
    attr_accessor :cmd
    attr_accessor :data
    def initialize(cmd, data)
     @cmd = cmd
     @data = data
    end
  end
end

lib/gdiff_copy.rb

require 'lib/gdiff_cmd'

module GDiff
  class GDiffCopy < GDiffCmd
 
    def initialize(position, length)
      @cmd = 249
      @data = [0]
      @data << position
      @data << length
    end
  end
end


lib/gdiff_data.rb

require 'lib/gdiff_cmd'

module GDiff
 
  class GDiffData < GDiffCmd
    def initialize(cmd, data)
      #if cmd < 1  or cmd > 248
      #  raise DataError
      #end
      @cmd = cmd
      @data = data
    end
  end
 
end

lib/gdiff_file.rb

module GDiff
 
  class GDiffFile < File
    @@magic = 0xd1ffd1ff
    @@version = 0x04
    @@EOF = 0
   
    def initialize(filename)
      @filename = filename
      @filedata = []
    end
   
    def put_header
      put_data(@@magic)
      put_data(@@version)
    end
   
    def put_trailer
      put_data(@@EOF)
    end
   
    def copy_byte(start)
      write_diff()
    end
   
    def put_data(data)
      if data.respond_to?(length) then
        if data.length==1 then
          @filedata << data
        else
          data.each_byte do |b|
          @filedata << data + ","
        end
      else
        @filedata << data
      end
    end
   
    def put_cmd(cmd)
      @filedata << cmd.cmd << ","
    end
   
    def put_cmd_and_data(cmd)
      put_cmd(cmd)
      put_data(cmd.data)
    end
   
    def write_diff
      p @filedata
      File.open(@filename, "w") { |f|
        f << @filedata.flatten
      }
    end
  end
end