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/** \file     BitStream.h

    \brief    class for handling bitstream (header)

*/

#pragma once

#include <stdint.h>

#include <vector>

#include <memory>

#include "CommonDef.h"

#if defined(TARGET_SIMD_X86) && SIMD_ENABLE

#  include "CommonDefX86.h"   // needed for simde_bswap64, but don't just include simde-common.h, because it breaks other files

#else

#  include "simde/simde-common.h"

#endif

namespace vvdec

{

// ====================================================================================================================

// Class definition

// ====================================================================================================================

/**

 * Model of an input bitstream that extracts bits from a predefined

 * bytestream.

 */

class InputBitstream

{

private:

  AlignedByteVec        m_fifo;   /// FIFO for storage of complete bytes

  std::vector<uint32_t> m_emulationPreventionByteLocation;

  uint32_t m_fifo_idx = 0;   /// Read index into m_fifo

  uint32_t m_num_held_bits = 0;

  uint64_t m_held_bits     = 0;

  bool m_zeroByteAdded = false;

#if ENABLE_TRACING

  uint32_t m_numBitsRead   = 0;

#endif

public:

  /**

   * Create a new bitstream reader object that reads from buf.

   */

  InputBitstream()  = default;

  ~InputBitstream() = default;

  CLASS_COPY_MOVE_DEFAULT( InputBitstream )

  void resetToStart();

  void inputZeroByte() { if( !m_zeroByteAdded ) m_fifo.push_back(0); };

  // interface for decoding

  uint32_t       peekBits( uint32_t uiNumberOfBits );

  uint32_t       read    ( uint32_t uiNumberOfBits );

  inline uint8_t readByte()

  {

#if ENABLE_TRACING

    m_numBitsRead += 8;

#endif

    if( m_num_held_bits )

    {

      CHECKD( m_num_held_bits & 7, "held bits should be byte-aligned" );

    }

    else

    {

      load_next_bits( 8 );

    }

    uint32_t uiBits = 0xff & ( m_held_bits >> ( m_num_held_bits - 8 ) );

    m_num_held_bits -= 8;

    return uiBits;

  }

  // In the function initBitstream, add a Byte at the end of m_fifo

  // In the past, readByteFlag judged whether to read data according to the flag, so it would not cross the boundary

  // Now, in order to speed up, readByteFlag will definitely read data, so it may cross the boundary

  inline uint8_t readByteFlag( uint8_t flag )

  {

#if ENABLE_TRACING

    m_numBitsRead += (flag & 1) * 8;

#endif

    if( m_num_held_bits )

    {

      CHECKD( m_num_held_bits & 7, "held bits should be byte-aligned" );

    }

    else

    {

      load_next_bits( 8 );

    }

    uint32_t uiBits = flag & ( m_held_bits >> ( m_num_held_bits - 8 ) );

    m_num_held_bits -= 8 * ( flag & 1 );

    return uiBits;

  }

  inline uint8_t peekPreviousByte()

  {

    CHECKD( m_num_held_bits & 7, "held bits should be byte-aligned" );

    // We don't know if m_heldBits actually contains the previous byte, because readByteFlag()

    // sometimes refills m_heldBits, but doesn't actually consume any of the loaded bits. So

    // we always need to look at the actual data buffer.

    const unsigned held_bytes = m_num_held_bits >> 3;

    CHECK( m_fifo_idx - held_bytes - 1 >= m_fifo.size(), "Exceeded FIFO size" );

    return m_fifo[m_fifo_idx - held_bytes - 1];

  }

  uint32_t         readOutTrailingBits();

  inline uint8_t   getHeldBits()     { return m_held_bits; }

  inline uint32_t  getByteLocation()

  {

    CHECKD( m_num_held_bits & 7, "held bits should be byte-aligned" );

    return m_fifo_idx - m_num_held_bits / 8;

  }

  inline uint8_t  getNumBitsUntilByteAligned() const { return m_num_held_bits & ( 0x7 ); }

  inline uint32_t getNumBitsLeft()             const { return ( m_fifo_idx < m_fifo.size() ? 8 * ( (uint32_t) m_fifo.size() - m_fifo_idx ) : 0 ) + m_num_held_bits; }

#if ENABLE_TRACING

  inline uint32_t getNumBitsRead()             const { return m_numBitsRead; }

#endif

  uint32_t        readByteAlignment();

  std::unique_ptr<InputBitstream> extractSubstream( uint32_t uiNumBits );   // Read the nominated number of bits, and return as a bitstream.

  void                         pushEmulationPreventionByteLocation( uint32_t pos )                    { m_emulationPreventionByteLocation.push_back( pos ); }

  uint32_t                     numEmulationPreventionBytesRead()                                      { return (uint32_t) m_emulationPreventionByteLocation.size(); }

  uint32_t                     getEmulationPreventionByteLocation( uint32_t idx )                     { return m_emulationPreventionByteLocation[idx]; }

  const std::vector<uint32_t>& getEmulationPreventionByteLocation() const                             { return m_emulationPreventionByteLocation; }

  void                         setEmulationPreventionByteLocation( const std::vector<uint32_t>& vec ) { m_emulationPreventionByteLocation = vec; }

  void                         clearEmulationPreventionByteLocation()                                 { m_emulationPreventionByteLocation.clear(); }

  const AlignedByteVec& getFifo() const { return m_fifo; }

        AlignedByteVec& getFifo()       { return m_fifo; }

  void                  clearFifo()     { m_fifo.clear(); m_zeroByteAdded = false; }

private:

  inline void load_next_bits( int requiredBits )

  {

    uint32_t num_bytes_to_load = 8;

    if UNLIKELY( m_fifo_idx + num_bytes_to_load > m_fifo.size()   // end of bitstream

                 || ( m_fifo_idx & 0x7 ) != 0 )                   // unaligned read position (m_fifo should be aligned)

    {

      const int required_bytes = ( requiredBits + 7 ) >> 3;

      CHECK( m_fifo_idx + required_bytes > m_fifo.size(), "Exceeded FIFO size" );

      num_bytes_to_load = (uint32_t)m_fifo.size() - m_fifo_idx;

      m_held_bits = 0;

      switch( num_bytes_to_load )

      {

      default: num_bytes_to_load = 8;   // in the unaligned case num_bytes_to_load could be >8

      case 8:  m_held_bits =  static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 7 * 8 );

      case 7:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 6 * 8 );

      case 6:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 5 * 8 );

      case 5:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 4 * 8 );

      case 4:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 3 * 8 );

      case 3:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 2 * 8 );

      case 2:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] ) << ( 1 * 8 );

      case 1:  m_held_bits |= static_cast<uint64_t>( m_fifo[m_fifo_idx++] );

      }

    }

    else

    {

      CHECKD( reinterpret_cast<intptr_t>( &m_fifo[m_fifo_idx] ) & 0x7, "bistream read pos unaligned" );

      m_held_bits = simde_bswap64( *reinterpret_cast<uint64_t*>( &m_fifo[m_fifo_idx] ) );

      m_fifo_idx += num_bytes_to_load;

    }

    m_num_held_bits = num_bytes_to_load * 8;

  }

};

}