text: // Copyright 2017 PDFium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
  
  #include "core/fpdfapi/parser/cpdf_seekablemultistream.h"
  
  #include <algorithm>
  
  #include "core/fpdfapi/parser/cpdf_stream_acc.h"
  #include "third_party/base/logging.h"
  #include "third_party/base/stl_util.h"
  
  CPDF_SeekableMultiStream::CPDF_SeekableMultiStream(
      const std::vector<const CPDF_Stream*>& streams) {
    for (const CPDF_Stream* pStream : streams) {
      m_Data.push_back(pdfium::MakeRetain<CPDF_StreamAcc>(pStream));
      m_Data.back()->LoadAllDataFiltered();
    }
  }
  
  CPDF_SeekableMultiStream::~CPDF_SeekableMultiStream() {}
  
  FX_FILESIZE CPDF_SeekableMultiStream::GetSize() {
    uint32_t dwSize = 0;
    for (const auto& acc : m_Data)
      dwSize += acc->GetSize();
    return dwSize;
  }
  
  bool CPDF_SeekableMultiStream::ReadBlockAtOffset(void* buffer,
                                                   FX_FILESIZE offset,
                                                   size_t size) {
    int32_t iCount = pdfium::CollectionSize<int32_t>(m_Data);
    int32_t index = 0;
    while (index < iCount) {
      const auto& acc = m_Data[index];
      FX_FILESIZE dwSize = acc->GetSize();
      if (offset < dwSize)
        break;
  
      offset -= dwSize;
      index++;
    }
    while (index < iCount) {
      const auto& acc = m_Data[index];
      uint32_t dwSize = acc->GetSize();
      size_t dwRead = std::min(size, static_cast<size_t>(dwSize - offset));
      memcpy(buffer, acc->GetSpan().subspan(offset, dwRead).data(), dwRead);
      size -= dwRead;
      if (size == 0)
        return true;
  
      buffer = static_cast<uint8_t*>(buffer) + dwRead;
      offset = 0;
      index++;
    }
    return false;
  }
  
  size_t CPDF_SeekableMultiStream::ReadBlock(void* buffer, size_t size) {
    NOTREACHED();
    return 0;
  }
  
  FX_FILESIZE CPDF_SeekableMultiStream::GetPosition() {
    return 0;
  }
  
  bool CPDF_SeekableMultiStream::IsEOF() {
    return false;
  }
  
  bool CPDF_SeekableMultiStream::Flush() {
    NOTREACHED();
    return false;
  }
  
  bool CPDF_SeekableMultiStream::WriteBlockAtOffset(const void* pData,
                                                    FX_FILESIZE offset,
                                                    size_t size) {
    NOTREACHED();
    return false;
  }
  