using System;

namespace Sandbox;

public static partial class NetworkStorage
{
	private static byte[][] Aes256ExpandKey( byte[] key )
	{
		const int nk = 8;
		const int nb = 4;
		const int nr = 14;
		var w = new byte[nb * (nr + 1)][];
		for ( var i = 0; i < nk; i++ )
			w[i] = new[] { key[4 * i], key[4 * i + 1], key[4 * i + 2], key[4 * i + 3] };
		for ( var i = nk; i < w.Length; i++ )
		{
			var temp = CopyBytes( w[i - 1] );
			if ( i % nk == 0 )
			{
				temp = SubWord( RotWord( temp ) );
				temp[0] ^= Rcon[i / nk];
			}
			else if ( i % nk == 4 )
			{
				temp = SubWord( temp );
			}
			w[i] = new byte[4];
			for ( var j = 0; j < 4; j++ )
				w[i][j] = (byte)(w[i - nk][j] ^ temp[j]);
		}
		return w;
	}

	private static byte[] AesEncryptBlock( byte[] input, byte[][] w )
	{
		var state = new byte[16];
		Array.Copy( input, state, 16 );
		AddRoundKey( state, w, 0 );
		for ( var round = 1; round < 14; round++ )
		{
			SubBytes( state );
			ShiftRows( state );
			MixColumns( state );
			AddRoundKey( state, w, round );
		}
		SubBytes( state );
		ShiftRows( state );
		AddRoundKey( state, w, 14 );
		return state;
	}

	private static byte[] RotWord( byte[] word ) => new[] { word[1], word[2], word[3], word[0] };
	private static byte[] SubWord( byte[] word ) => new[] { SBox[word[0]], SBox[word[1]], SBox[word[2]], SBox[word[3]] };

	private static byte[] CopyBytes( byte[] source )
	{
		var copy = new byte[source.Length];
		Array.Copy( source, copy, source.Length );
		return copy;
	}

	private static void AddRoundKey( byte[] state, byte[][] w, int round )
	{
		for ( var c = 0; c < 4; c++ )
		for ( var r = 0; r < 4; r++ )
			state[c * 4 + r] ^= w[round * 4 + c][r];
	}

	private static void SubBytes( byte[] state )
	{
		for ( var i = 0; i < state.Length; i++ )
			state[i] = SBox[state[i]];
	}

	private static void ShiftRows( byte[] s )
	{
		(s[1], s[5], s[9], s[13]) = (s[5], s[9], s[13], s[1]);
		(s[2], s[6], s[10], s[14]) = (s[10], s[14], s[2], s[6]);
		(s[3], s[7], s[11], s[15]) = (s[15], s[3], s[7], s[11]);
	}

	private static void MixColumns( byte[] s )
	{
		for ( var c = 0; c < 4; c++ )
		{
			var i = c * 4;
			var a0 = s[i];
			var a1 = s[i + 1];
			var a2 = s[i + 2];
			var a3 = s[i + 3];
			s[i] = (byte)(Gmul2( a0 ) ^ Gmul3( a1 ) ^ a2 ^ a3);
			s[i + 1] = (byte)(a0 ^ Gmul2( a1 ) ^ Gmul3( a2 ) ^ a3);
			s[i + 2] = (byte)(a0 ^ a1 ^ Gmul2( a2 ) ^ Gmul3( a3 ));
			s[i + 3] = (byte)(Gmul3( a0 ) ^ a1 ^ a2 ^ Gmul2( a3 ));
		}
	}

	private static byte Gmul2( byte x ) => (byte)((x << 1) ^ (((x >> 7) & 1) * 0x1b));
	private static byte Gmul3( byte x ) => (byte)(Gmul2( x ) ^ x);

	private static readonly byte[] Rcon = {
		0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
	};

	private static readonly byte[] SBox = {
		0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
		0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
		0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
		0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
		0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
		0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
		0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
		0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
		0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
		0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
		0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
		0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
		0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
		0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
		0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
		0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16
	};}