// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// This file contains an implementation of a H264BitstreamBuffer class for
// constructing raw bitstream buffers containing NAL units in
// H.264 Annex-B stream format.
// See H.264 spec Annex B and chapter 7for more details.

#ifndef MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_
#define MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_

#include "base/gtest_prod_util.h"
#include "base/numerics/safe_conversions.h"
#include "media/base/media_export.h"
#include "media/base/video_frame.h"
#include "media/filters/h264_parser.h"

namespace media {

// Holds one or more NALUs as a raw bitstream buffer in H.264 Annex-B format.
// Note that this class currently does NOT insert emulation prevention
// three-byte sequences (spec 7.3.1).
class MEDIA_EXPORT H264BitstreamBuffer {
 public:
  H264BitstreamBuffer();
  ~H264BitstreamBuffer();

  // Discard all data and reset the buffer for reuse.
  void Reset();

  // Append |num_bits| bits to the stream from |val|.
  // |val| is interpreted in the host endianness.
  template <typename T>
  void AppendBits(size_t num_bits, T val) {
    AppendU64(num_bits, static_cast<uint64>(val));
  }

  void AppendBits(size_t num_bits, bool val) {
    DCHECK_EQ(num_bits, 1ul);
    AppendBool(val);
  }

  // Append a one-bit bool/flag value |val| to the stream.
  void AppendBool(bool val);

  // Append a signed value in |val| in Exp-Golomb code.
  void AppendSE(int val);

  // Append an unsigned value in |val| in Exp-Golomb code.
  void AppendUE(unsigned int val);

  // Start a new NALU of type |nalu_type| and with given |nal_ref_idc|
  // (see spec). Note, that until FinishNALU() is called, some of the bits
  // may not be flushed into the buffer and the data will not be correctly
  // aligned with trailing bits.
  void BeginNALU(H264NALU::Type nalu_type, int nal_ref_idc);

  // Finish current NALU. This will flush any cached bits and correctly align
  // the buffer with RBSP trailing bits. This MUST be called for the stream
  // returned by data() to be correct.
  void FinishNALU();

  // Return number of full bytes in the stream. Note that FinishNALU() has to
  // be called to flush cached bits, or the return value will not include them.
  size_t BytesInBuffer();

  // Return a pointer to the stream. FinishNALU() must be called before
  // accessing the stream, otherwise some bits may still be cached and not
  // in the buffer.
  uint8* data();

 private:
  FRIEND_TEST_ALL_PREFIXES(H264BitstreamBufferAppendBitsTest,
                           AppendAndVerifyBits);

  // Allocate additional memory (kGrowBytes bytes) for the buffer.
  void Grow();

  // Append |num_bits| bits from U64 value |val| (in host endianness).
  void AppendU64(size_t num_bits, uint64 val);

  // Flush any cached bits in the reg with byte granularity, i.e. enough
  // bytes to flush all pending bits, but not more.
  void FlushReg();

  typedef uint64 RegType;
  enum {
    // Sizes of reg_.
    kRegByteSize = sizeof(RegType),
    kRegBitSize = kRegByteSize * 8,
    // Amount of bytes to grow the buffer by when we run out of
    // previously-allocated memory for it.
    kGrowBytes = 4096,
  };

  COMPILE_ASSERT(kGrowBytes >= kRegByteSize,
                 kGrowBytes_must_be_larger_than_kRegByteSize);

  // Unused bits left in reg_.
  size_t bits_left_in_reg_;

  // Cache for appended bits. Bits are flushed to data_ with kRegByteSize
  // granularity, i.e. when reg_ becomes full, or when an explicit FlushReg()
  // is called.
  RegType reg_;

  // Current capacity of data_, in bytes.
  size_t capacity_;

  // Current byte offset in data_ (points to the start of unwritten bits).
  size_t pos_;

  // Buffer for stream data.
  uint8* data_;
};

}  // namespace media

#endif  // MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_
