var
  FCache1: TTntStringList;
  FCache1Vals: TTntStringList;
  FCache2: TTntStringList;
  FCache2Vals: TTntStringList;

function Initialize: Boolean;
begin
  result := True;
end;

procedure Finalize;
begin
end;

procedure BeginSort;
begin
  FCache1 := TTntStringList.Create;
  FCache1Vals := TTntStringList.Create;
  FCache2 := TTntStringList.Create;
  FCache2Vals := TTntStringList.Create;
  FCache1.Sorted := True;
  FCache2.Sorted := True;
end;

procedure EndSort;
begin
  FCache2Vals.Free;
  FCache2.Free;
  FCache1Vals.Free;
  FCache1.Free;
end;

function IndexValueForImage(AImage: TImageItem): WideString;
begin
  result := AddLeadingChars(IntToStr(AImage._VersionCount), '0', 9, False) +
            AImage.FileNameOnly;
end;

function Sort (AItem1, AItem2: TImageItem): Integer;
var
  AIdx: Integer;
  AVal1, AVal2: WideString;
begin
  result := 0;
  if AItem1 = AItem2 then exit;

  AIdx := FCache1.IndexOf(AItem1.GUID);
  if AIdx = -1 then
  begin
    AVal1 := IndexValueForImage(AItem1);
    AIdx := FCache1Vals.Add(AVal1);
    FCache1.AddObject(AItem1.GUID, IntToStr(AIdx));
  end
  else
    AVal1 := FCache1Vals.Strings[FCache1.Objects[AIdx]];

  AIdx := FCache2.IndexOf(AItem2.GUID);
  if AIdx = -1 then
  begin
    AVal2 := IndexValueForImage(AItem2);
    AIdx := FCache2Vals.Add(AVal2);
    FCache2.AddObject(AItem2.GUID, IntToStr(AIdx));
  end
  else
    AVal2 := FCache2Vals.Strings[FCache2.Objects[AIdx]];

  if AVal1 = AVal2 then
    result := 0
  else if AVal1 > AVal2 then
    result := 1
  else
    result := -1;
end;