unit StrStrm;

interface

uses
  SysUtils, Classes;

const
  DEFAULT_PAGE_SIZE = 65536; // 64k

type
  TStringStreamer = class
    private
      fStream: TFileStream;
      fFileName: string;
      fPageSize: integer;
      fPagesLoaded: integer;
      fLinesRead: integer;
      fStr: string;
      fLen: integer;
      fOffset: integer;
      fLastPage: boolean;
    protected
      procedure LoadNextPage;
      property Stream: TFileStream read fStream;
      property LastPage: boolean read fLastPage;
    public
      constructor Create(const AFileName: string; AShare: boolean = true;
                         APageSize: integer = DEFAULT_PAGE_SIZE);
      destructor Destroy; override;
      procedure Reset;
      function NextLine: string;
      function Eof: boolean;
      property FileName: string read fFileName;
      property PageSize: integer read fPageSize;
      property PagesLoaded: integer read fPagesLoaded;
      property LinesRead: integer read fLinesRead;
  end;//of class

implementation

{ ### TStringFile ############################################################ }

constructor TStringStreamer.Create(const AFileName: string; AShare: boolean = true;
                                   APageSize: integer = DEFAULT_PAGE_SIZE);
  begin
    fFileName:=AFileName;
    if APageSize <= 0 then APageSize:=DEFAULT_PAGE_SIZE;
    fPageSize:=APageSize;
    if AShare then fStream:=TFileStream.Create(AFileName,fmOpenRead or fmShareDenyWrite)
    else fStream:=TFileStream.Create(AFileName,fmOpenRead or fmShareExclusive);
    SetString(fStr,nil,ApageSize);
    LoadNextPage;
  end;

destructor TStringStreamer.Destroy;
  begin
    fStream.Free;
    inherited;
  end;

  { ### protected ### }

procedure TStringStreamer.LoadNextPage;
  begin
    fStr[1]:=#0;
    fLen:=Stream.Read(pointer(fStr)^,fPageSize);
    fOffset:=1;
    fLastPage:=fLen < fPageSize;
    inc(fPagesLoaded);
  end;

  { ### public ### }

procedure TStringStreamer.Reset;
  begin
    Stream.Position:=0;
    fPagesLoaded:=0;
    LoadNextPage;
    fLinesRead:=0;
  end;

function TStringStreamer.NextLine: string;
  label CONTINUE_LINE;
  var Prev: string;
      P: PChar;
      Start: PChar;
      FullLine: boolean;
      S: string;
  begin
    Prev:='';
    Result:='';
CONTINUE_LINE:
    FullLine:=false;
    P:=@fStr[fOffset];
    Start:=P;
    while fOffset <= fLen do begin
        if P^ in [#0, #10, #13] then begin
            FullLine:=true;
            Break;
        end;
        inc(P);
        inc(fOffset);
    end;
    SetString(S,Start,P-Start);
    if FullLine then begin
        if pointer(Prev) <> nil then Result:=Prev+S
        else Result:=S;
        if P^ = #13 then begin
            inc(P);
            inc(fOffset);
        end;
        if P^ = #10 then begin
            inc(P);
            inc(fOffset);
        end;
        if P^ = #0 then begin
            //inc(P);
            inc(fOffset);
        end;
    end else begin
        if pointer(Prev) <> nil then Prev:=Prev+S
        else Prev:=S;
        if not Eof then begin
            LoadNextPage;
            goto CONTINUE_LINE
        end else Result:=Prev;
    end;
    inc(fLinesRead)
  end;

function TStringStreamer.Eof: boolean;
  begin
    Result:=LastPage and (fOffset > fLen);
  end;

{ ############################################################################ }

end.