program Rehash;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  Classes,
  zlib,
  Math,
  AnsiStrings,
  StrUtils,
  sha1;

var
  ms1, ms2, ms3: TMemoryStream;
  z: TZCompressionStream;
  i, j: Integer;
  b, count: Byte;
  size: Integer;
  temp: Cardinal;

  s2: RawByteString;
  ctx: TSHA1Context;
  dig: TSHA1Digest;
  ba: PByteArray;

const
  Base64: AnsiString = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+\'; // Achtung: Unterschiedlich!

begin
  try
    writeln('Snapshot-SHA-1-Hash-Neuberechner (Stand-Alone) // yat.qa // 11. Dezember 2016');
    ms1 := TMemoryStream.Create;
    ms2 := TMemoryStream.Create;
    ms1.LoadFromFile(paramstr(1));
    // Absätze am Ende erkennen
    Size := ms1.Size;
    repeat
      dec(Size);
      ms1.Position := Size;
      ms1.ReadBuffer(b, 1);
    until (b <> $0a) and (b <> $0d);
    //inc(size);
    writeln(ms1.Size - Size - 1, ' Bytes am Ende entfernt');
    ms1.Position := 0;
    // BOM erkennen
    ms1.ReadBuffer(b, 1);
    if b = $ef then
    ms1.ReadBuffer(temp, 2)
    else
    ms1.Position := 0;
    // SHA-1 berechnen
    ms2.CopyFrom(ms1, 5);
    write('Alter Hash: ');
    while True do
    begin
      ms1.Read(b, 1);
      if b = $7c then
      Break;
      write(AnsiChar(b));
    end;
    ms1.Position := ms1.Position - 1;
    writeln;
    //ms1.Position := ms1.Position + 34;
    sha1init(ctx);
    ba := ms1.Memory;
    SHA1Update(ctx, ba[ms1.Position + 1], Size - ms1.Position);
    ba := nil; // braucht man das?
    dig := SHA1Final(ctx);
    ms3 := TMemoryStream.Create;
    ms3.WriteBuffer(dig, 20);
    ms3.Position := 0;
    //for i := 0 to 19 do
    //write(IntToHex(dig[i], 2));
    // Base64-Encoder (binary-safe), feste Größe von 20 Byte (27+1 Zeichen)
    Count := 3; // Compiler-Blabla
    write('Neuer Hash: ');
    for i := 0 to 6 do
    begin
      count := Min(20 - i * 3, 3);
      ms3.ReadBuffer(temp, Count);
      temp := temp and $ff00 + temp shl 16 + (temp shr 16) and $ff; // Endianness drehen (vereinfacht weil nur 3 Byte verwendet)
      for j := 0 to Count do
      begin
        b := Byte(Base64[(temp shr 18) and $3f + 1]);
        temp := temp shl 6;
        ms2.WriteBuffer(b, 1);
        write(AnsiChar(b));
        if b = $5c then
        begin
          b := $2F;
          ms2.WriteBuffer(b, 1);
          write(AnsiChar(b));
        end;
      end;
    end;
    writeln('=');
    b := $3D;
    ms2.WriteBuffer(b, 1);

    ms2.CopyFrom(ms1, Size - ms1.Position + 1);
    ms2.SaveToFile(paramstr(1) + '.new');


    writeln('Erfolgreich neu berechnet!');
  except
    on E:Exception do
      Writeln(E.Classname, ': ', E.Message);
  end;
  readln;
end.