#include "dng_jpeg_memory_source.h"

#if qDNGUseLibJPEG

#include "dng_safe_arithmetic.h"

namespace {

void InitSource(j_decompress_ptr cinfo) {

  // No initialization necessary.

}

boolean FillInputBuffer(j_decompress_ptr cinfo) {

  // We already filled the buffer with all of the data when the source was

  // initialized, so we can't get any more data.

  ERREXIT(cinfo, JERR_INPUT_EOF);

  return FALSE;

}

void SkipInputData(j_decompress_ptr cinfo, long num_bytes) {

  if (num_bytes > 0) {

    // Convert num_bytes to a size_t.

    // We've established that num_bytes is positive, to it's safe to cast it

    // to an unsigned long.

    size_t num_bytes_as_size_t = 0;

    try {

      ConvertUnsigned(static_cast<unsigned long>(num_bytes),

                      &num_bytes_as_size_t);

    } catch (const dng_exception &e) {

      ERREXIT(cinfo, JERR_INPUT_EOF);

      return;

    }

    jpeg_source_mgr *source_manager =

        reinterpret_cast<jpeg_source_mgr *>(cinfo->src);

    // Advance the current position by the given number of bytes.

    if (num_bytes_as_size_t <= source_manager->bytes_in_buffer) {

      source_manager->bytes_in_buffer -= num_bytes_as_size_t;

      source_manager->next_input_byte += num_bytes_as_size_t;

    } else {

      // Tried to read beyond the end of the buffer.

      ERREXIT(cinfo, JERR_INPUT_EOF);

      return;

    }

  }

}

boolean ResyncToRestart(j_decompress_ptr cinfo, int desired) {

  // Can't resync.

  return FALSE;

}

void TermSource(j_decompress_ptr cinfo) {

  // No termination necessary.

}

}  // namespace

jpeg_source_mgr CreateJpegMemorySource(const uint8 *buffer, size_t size) {

  jpeg_source_mgr source;

  source.next_input_byte = reinterpret_cast<const JOCTET *>(buffer);

  source.bytes_in_buffer = size;

  // Initialize function pointers.

  source.init_source = InitSource;

  source.fill_input_buffer = FillInputBuffer;

  source.skip_input_data = SkipInputData;

  source.resync_to_restart = ResyncToRestart;

  source.term_source = TermSource;

  return source;

}

#endif  // qDNGUseLibJPEG