Delphi - Compare and Mark String Differences

Question

What I need to do is compare two strings and mark the differences with begining/ending marks for changes. Example:

this is string number one.

this string is string number two.

output would be

this [is|string is] string number [one|two].  

I've been trying to figure this out for some time now. And I found something I blieved would help me do this, but I am unable to make this happen.
http://www.angusj.com/delphi/textdiff.html

I have it about 80% working here, but I've got no idea how to get it to do exactly what I want it to do. Any help would be appreciated.

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Diff, StdCtrls;

type
  TForm2 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    Memo1: TMemo;
    Diff: TDiff;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;
  s1,s2:string;

implementation

{$R *.dfm}

procedure TForm2.Button1Click(Sender: TObject);
var
  i: Integer;
  lastKind: TChangeKind;

  procedure AddCharToStr(var s: string; c: char; kind, lastkind: TChangeKind);
  begin
    if (kind  lastkind) AND (lastkind = ckNone) and (kind  ckNone) then s:=s+'[';
    if (kind  lastkind) AND (lastkind  ckNone) and (kind = ckNone) then s:=s+']';
    case kind of         
      ckNone: s := s  + c;
      ckAdd: s := s + c;         
      ckDelete: s := s  + c;
      ckModify: s := s + '|' + c;
    end;
  end;

begin
  Diff.Execute(pchar(edit1.text), pchar(edit2.text), length(edit1.text), length(edit2.text));

  //now, display the diffs ...
  lastKind := ckNone;
  s1 := ''; s2 := '';
  form2.caption:= inttostr(diff.Count);
  for i := 0 to Diff.count-1 do
  begin

    with Diff.Compares[i] do
    begin
      //show changes to first string (with spaces for adds to align with second string)
      if Kind = ckAdd then 
      begin 
        AddCharToStr(s1,' ',Kind, lastKind); 
      end
      else 
      AddCharToStr(s1,chr1,Kind,lastKind);
      if Kind = ckDelete then 
      begin 
        AddCharToStr(s2,' ',Kind, lastKind)
      end
      else AddCharToStr(s2,chr2,Kind,lastKind);

      lastKind := Kind;
    end;
  end;
    memo1.Lines.Add(s1);
    memo1.Lines.Add(s2);
end;

end.

I took the basicdemo1 from angusj.com and modified it to get this far.

Answer 1

There is an Object Pascal Diff Engine available which might be of assistance. You might want to break each "word" into a separate line for the comparison, or modify the algorithm to compare on a word by word basis.