// Copyright (c) 2016 Dr. Colin Hirsch and Daniel Frey
// Please see LICENSE for license or visit https://github.com/taocpp/json/

#ifndef TAOCPP_JSON_INCLUDE_INTERNAL_SHA256_HH
#define TAOCPP_JSON_INCLUDE_INTERNAL_SHA256_HH

// Implements RFC 6234, SHA-256

#include <cstddef>
#include <cstdint>
#include <cstring>
#include <string>

#define DBL_INT_ADD(a,b,c) if (a > 0xffffffff - (c)) ++b; a += c;

// RFC 6234, 3.d; see also http://stackoverflow.com/a/4209604/2073257
#define ROR( x, N ) ( ( x >> N ) | ( x << ( 32 - N ) ) )

// RFC 6234, 5.1
#define CH( x, y, z ) ( ( x & y ) ^ ( ~x & z ) )
#define MAJ( x, y, z ) ( ( x & y ) ^ ( x & z ) ^ ( y & z ) )
#define BSIG0( x ) ( ROR( x, 2 ) ^ ROR( x, 13 ) ^ ROR( x, 22 ) )
#define BSIG1( x ) ( ROR( x, 6 ) ^ ROR( x, 11 ) ^ ROR( x, 25 ) )
#define SSIG0( x ) ( ROR( x, 7 ) ^ ROR( x, 18 ) ^ ( x >> 3 ) )
#define SSIG1( x ) ( ROR( x, 17 ) ^ ROR( x, 19 ) ^ ( x >> 10 ) )

namespace tao
{
   namespace json
   {
      namespace internal
      {
         // RFC 6234, 5.1
         static std::uint32_t K[ 64 ] = {
            0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
            0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
            0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
            0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
            0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
            0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
            0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
            0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
            0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
            0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
            0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
            0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
            0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
            0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
            0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
            0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
         };

         class sha256
         {
         private:
            unsigned char M[ 64 ];
            std::size_t size;

            std::uint32_t H[ 8 ];

            // RFC 6234, 6.2
            void process() noexcept
            {
               std::uint32_t W[ 64 ];

               // step 1
               for ( std::size_t t = 0, i = 0; t != 16; ++t, i += 4 ) {
                  W[ t ] = ( M[ i ] << 24 ) | ( M[ i + 1 ] << 16 ) | ( M[ i + 2 ] << 8 ) | ( M[ i + 3 ] );
               }
               for ( std::size_t t = 16; t != 64; ++t ) {
                  W[ t ] = SSIG1( W[ t - 2 ] ) + W[ t - 7 ] + SSIG0( W[ t - 15 ] ) + W[ t - 16 ];
               }

               // step 2
               std::uint32_t a, b, c, d, e, f, g, h;
               a = H[ 0 ];
               b = H[ 1 ];
               c = H[ 2 ];
               d = H[ 3 ];
               e = H[ 4 ];
               f = H[ 5 ];
               g = H[ 6 ];
               h = H[ 7 ];

               // step 3
               for ( std::size_t t = 0; t != 64; ++t ) {
                  const std::uint32_t T1 = h + BSIG1( e ) + CH( e, f, g ) + K[ t ] + W[ t ];
                  const std::uint32_t T2 = BSIG0( a ) + MAJ( a, b, c );
                  h = g;
                  g = f;
                  f = e;
                  e = d + T1;
                  d = c;
                  c = b;
                  b = a;
                  a = T1 + T2;
               }

               // step 4
               H[ 0 ] += a;
               H[ 1 ] += b;
               H[ 2 ] += c;
               H[ 3 ] += d;
               H[ 4 ] += e;
               H[ 5 ] += f;
               H[ 6 ] += g;
               H[ 7 ] += h;
            }

         public:
            sha256() noexcept
            {
               reset();
            }

            sha256( const sha256 & ) = delete;
            void operator= ( const sha256 & ) = delete;

            void reset() noexcept
            {
               size = 0;

               // RFC 6234, 6.1
               H[ 0 ] = 0x6a09e667;
               H[ 1 ] = 0xbb67ae85;
               H[ 2 ] = 0x3c6ef372;
               H[ 3 ] = 0xa54ff53a;
               H[ 4 ] = 0x510e527f;
               H[ 5 ] = 0x9b05688c;
               H[ 6 ] = 0x1f83d9ab;
               H[ 7 ] = 0x5be0cd19;
            }

            void feed( const unsigned char c ) noexcept
            {
               M[ size++ % 64 ] = c;
               if ( ( size % 64 ) == 0 ) {
                  process();
               }
            }

            void feed( const void * p, std::size_t s ) noexcept
            {
               const unsigned char * q = static_cast< const unsigned char * >( p );
               while ( s-- ) {
                  feed( *q++ );
               }
            }

            void feed( const std::string & v ) noexcept
            {
               feed( v.data(), v.size() );
            }

            // RFC 6234, 4.1
            void store_unsafe( unsigned char * buffer ) noexcept
            {
               std::size_t i = size % 64;
               if ( i < 56 ) {
                  M[ i++ ] = 0x80;
                  while ( i < 56 ) {
                     M[ i++ ] = 0x00;
                  }
               }
               else {
		  M[ i++ ] = 0x80;
                  while ( i < 64 ) {
                     M[ i++ ] = 0x00;
                  }
                  process();
                  std::memset( M, 0, 56 );
               }

               size *= 8;

               M[ 63 ] = size;
               M[ 62 ] = size >> 8;
               M[ 61 ] = size >> 16;
               M[ 60 ] = size >> 24;
               M[ 59 ] = size >> 32;
               M[ 58 ] = size >> 40;
               M[ 57 ] = size >> 48;
               M[ 56 ] = size >> 56;

               process();

               for ( std::size_t i = 0; i < 4; ++i ) {
                  buffer[ i ] = ( H[ 0 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 4 ] = ( H[ 1 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 8 ] = ( H[ 2 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 12 ] = ( H[ 3 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 16 ] = ( H[ 4 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 20 ] = ( H[ 5 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 24 ] = ( H[ 6 ] >> ( 24 - i * 8 ) ) & 0xff;
                  buffer[ i + 28 ] = ( H[ 7 ] >> ( 24 - i * 8 ) ) & 0xff;
               }
            }

            std::string get()
            {
               std::string result;
               result.resize( 32 );
               store_unsafe( (unsigned char *)( result.data() ) );
               return result;
            }
         };

      } // internal

   } // json

} // tao

#endif
