OCCT

// Copyright (c) 2017-2019 OPEN CASCADE SAS
//
// This file is part of Open CASCADE Technology software library.
//
// This library is free software; you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License version 2.1 as published
// by the Free Software Foundation, with special exception defined in the file
// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
// distribution for complete text of the license and disclaimer of any warranty.
//
// Alternatively, this file may be used under the terms of Open CASCADE
// commercial license or contractual agreement..

#ifndef _Standard_ReadBuffer_HeaderFile
#define _Standard_ReadBuffer_HeaderFile

#include <Standard_ProgramError.hxx>

#include <iostream>

//! Auxiliary tool for buffered reading from input stream within chunks of constant size.
class Standard_ReadBuffer
{
public:
  //! Constructor with initialization.
  Standard_ReadBuffer(int64_t theDataLen, size_t theChunkLen, bool theIsPartialPayload = false)
      : myBufferPtr(nullptr),
        myBufferEnd(nullptr),
        myDataLen(0),
        myDataRead(0),
        myChunkLen(0),
        myNbChunks(0),
        myBufferLen(0)
  {
    Init(theDataLen, theChunkLen, theIsPartialPayload);
  }

  //! Initialize the buffer.
  //! @param[in] theDataLen   the full length of input data to read from stream.
  //! @param[in] theChunkLen  the length of single chunk to read
  //! @param[in] theIsPartialPayload  when FALSE, theDataLen will be automatically aligned to the
  //! multiple of theChunkLen;
  //!                                 when TRUE, last chunk will be read from stream exactly till
  //!                                 theDataLen allowing portion of chunk to be uninitialized
  //!                                 (useful for interleaved data)
  void Init(int64_t theDataLen, size_t theChunkLen, bool theIsPartialPayload = false)
  {
    myDataRead = 0;
    if (theIsPartialPayload)
    {
      myDataLen = theDataLen;
    }
    else
    {
      myDataLen = theDataLen - theDataLen % int64_t(theChunkLen);
    }
    myChunkLen  = theChunkLen;
    myNbChunks  = sizeof(myBuffer) / theChunkLen;
    myBufferLen = theChunkLen * myNbChunks;

    myBufferEnd = myBuffer + sizeof(myBuffer);
    myBufferPtr = myBuffer + sizeof(myBuffer);
    memset(myBuffer, 0, sizeof(myBuffer));

    if (theChunkLen > sizeof(myBuffer))
    {
      throw Standard_ProgramError(
        "Internal error - chunk size is greater then preallocated buffer");
    }
  }

  //! Return TRUE if amount of read bytes is equal to requested length of entire data.
  bool IsDone() const { return myDataRead == myDataLen; }

  //! Read next chunk.
  //! @return pointer to the chunk or NULL on error / end of reading buffer
  template <typename Chunk_T, typename Stream_T>
  Chunk_T* ReadChunk(Stream_T& theStream)
  {
    return reinterpret_cast<Chunk_T*>(readRawDataChunk(theStream));
  }

  //! Read next chunk.
  //! @return pointer to the chunk or NULL on error / end of reading buffer
  template <typename Stream_T>
  char* ReadDataChunk(Stream_T& theStream)
  {
    return readRawDataChunk(theStream);
  }

private:
  //! Read next chunk.
  //! @return pointer to the chunk or NULL on error / end of reading buffer
  template <typename Stream_T>
  char* readRawDataChunk(Stream_T& theStream)
  {
    if (myBufferPtr == nullptr)
    {
      return nullptr;
    }

    myBufferPtr += myChunkLen;
    if (myBufferPtr < myBufferEnd)
    {
      return myBufferPtr;
    }

    const int64_t aDataLeft = myDataLen - myDataRead;
    if (aDataLeft <= 0) // myDataLen is normally multiple of myChunkLen, but can be smaller in
                        // interleaved data
    {
      myBufferPtr = nullptr;
      return nullptr;
    }

    const size_t aDataToRead = int64_t(myBufferLen) > aDataLeft ? size_t(aDataLeft) : myBufferLen;
    if (!readStream(theStream, aDataToRead))
    {
      myBufferPtr = nullptr;
      return nullptr;
    }

    myBufferPtr = myBuffer;
    myBufferEnd = myBuffer + aDataToRead;
    myDataRead += aDataToRead;
    return myBufferPtr;
  }

  //! Read from stl stream.
  bool readStream(std::istream& theStream, size_t theLen)
  {
    theStream.read(myBuffer, theLen);
    return theStream.good();
  }

  //! Read from FILE stream.
  bool readStream(FILE* theStream, size_t theLen)
  {
    return ::fread(myBuffer, 1, theLen, theStream) == theLen;
  }

private:
  char        myBuffer[4096]; //!< data cache
  char*       myBufferPtr;    //!< current position within the buffer
  const char* myBufferEnd;    //!< end of the buffer
  int64_t     myDataLen;      //!< length of entire data to read
  int64_t     myDataRead;     //!< amount of data already processed
  // clang-format off
  size_t      myChunkLen;     //!< length of single chunk that caller would like to read (e.g. iterator increment)
  size_t      myNbChunks;     //!< number of cached chunks
  size_t      myBufferLen;    //!< effective length of the buffer to be read at once (multiple of chunk length)
  // clang-format on
};

#endif // _Standard_ReadBuffer_HeaderFile