unit circularbuffers;

type
  PByte = ^Byte;
  
type
  TCircularBufferOfByteRec = record
    Head, Tail: ^Byte;       // Pointers to the head and tail of the data in the buffer
    MaxCount: Word;          // MaxCount that was stored in the buffer
    Size: Word;              // Size of the Buffer
    Count: Word;             // Current count in the buffer
    BufferPtr: ^Byte;        // Pointer to the buffer that contains the data
  end;
  
  TCircularBuffer256 = array[256] of Byte;
  TCircularBuffer1024 = array[1024] of Byte;
  
procedure CircularBuffers_Initialize(BufferPtr: PByte; ASize: Word; var Buffer: TCircularBufferOfByteRec);
function CircularBuffers_Add(var Buffer: TCircularBufferOfByteRec; DataBytes: PByte; Count: Word): Boolean;
function CircularBuffers_AddByte(var Buffer: TCircularBufferOfByteRec; DataByte: Byte): Boolean;
function CircularBuffers_Remove(var Buffer: TCircularBufferOfByteRec; DataBytes: PByte; var Count: Word): Boolean;
function CircularBuffers_RemoveByte(var Buffer: TCircularBufferOfByteRec): Byte;

implementation

procedure CircularBuffers_Initialize(BufferPtr: PByte; ASize: Word; var Buffer: TCircularBufferOfByteRec);
begin
  Buffer.BufferPtr := BufferPtr;
  Buffer.MaxCount := 0;
  Buffer.Size := ASize;
  Buffer.Count := 0;
  Buffer.Head := BufferPtr;
  Buffer.Tail := BufferPtr;
end;

function CircularBuffers_Add(var Buffer: TCircularBufferOfByteRec; DataBytes: PByte; Count: Word): Boolean;
var
  i: Word;
  EmptySize: Word;
  LastBytePtr: ^Byte;
begin
  EmptySize := Buffer.Size - Buffer.Count;  
  LastBytePtr := Buffer.BufferPtr + Buffer.Size;
  if Count <= EmptySize then
  begin
    if Count + Buffer.Count > Buffer.MaxCount then
      Buffer.MaxCount := Count + Buffer.Count;
    i := 0;
    while i < Count do
    begin
      Buffer.Head^ := DataBytes^;
      Inc(Buffer.Head);
      Inc(DataBytes);
      if Buffer.Head >= LastBytePtr then
        Buffer.Head := Buffer.BufferPtr;         // Wrap if necessary
      Inc(i)
    end;
    Buffer.Count := Buffer.Count + Count;
    Result := True;
  end else
    Result := False;
end;

function CircularBuffers_AddByte(var Buffer: TCircularBufferOfByteRec; DataByte: Byte): Boolean;
begin
  Result := False;
  if Buffer.Count < Buffer.Size then
  begin
    Buffer.Head^ := DataByte;
    Inc(Buffer.Head);
    Inc(Buffer.Count);
    if Buffer.Count > Buffer.MaxCount then
      Buffer.MaxCount := Buffer.Count;
    if Buffer.Head >= (Buffer.BufferPtr + Buffer.Size) then
      Buffer.Head := Buffer.BufferPtr;                                          // Wrap if Necessary
    Result := True;
    
  //  UART2_Write( Char(DataByte));
    
  end;
end;

function CircularBuffers_Remove(var Buffer: TCircularBufferOfByteRec; DataBytes: PByte; var Count: Word): Boolean;
var
  i: Word;
  LastBytePtr: PByte;
  ResultCount: Word;
begin
  Result := False;
  LastBytePtr := Buffer.BufferPtr + Buffer.Size;
  ResultCount := 0;
  i := 0;
  while i < Count do
  begin
    DataBytes^ := Buffer.Tail^;
    Inc(Buffer.Tail); 
    Inc(ResultCount);
    if Buffer.Tail >= LastBytePtr then
      Buffer.Tail := Buffer.BufferPtr;                                          // Wrap if Necessary
    Inc(i);
  end;
  Buffer.Count := Buffer.Count - ResultCount;
  Count := ResultCount;
end;

function CircularBuffers_RemoveByte(var Buffer: TCircularBufferOfByteRec): Byte;
begin
  Result := #0;
  if Buffer.Count > 0 then
  begin
    Result := Buffer.Tail^;
    Inc(Buffer.Tail);
    Dec(Buffer.Count);
    if Buffer.Tail >= (Buffer.BufferPtr + Buffer.Size) then
      Buffer.Tail := Buffer.BufferPtr;                                          // Wrap if Necessary

  //  UART2_Write( Char(Result));
  end;
end;

end.