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using System;
using System.Buffers.Binary;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
namespace Impostor.Api.Innersloth
{
public static class GameCodeParser
{
private const string V2 = "QWXRTYLPESDFGHUJKZOCVBINMA";
private static readonly int[] V2Map = {
25,
21,
19,
10,
8,
11,
12,
13,
22,
15,
16,
6,
24,
23,
18,
7,
0,
3,
9,
4,
14,
20,
1,
2,
5,
17
};
private static readonly RNGCryptoServiceProvider Random = new RNGCryptoServiceProvider();
public static string IntToGameName(int input)
{
// V2.
if (input < -1)
{
return IntToGameNameV2(input);
}
// V1.
Span<byte> code = stackalloc byte[4];
BinaryPrimitives.WriteInt32LittleEndian(code, input);
#if NETSTANDARD2_0
return Encoding.UTF8.GetString(code.Slice(0, 4).ToArray());
#else
return Encoding.UTF8.GetString(code.Slice(0, 4));
#endif
}
private static string IntToGameNameV2(int input)
{
var a = input & 0x3FF;
var b = (input >> 10) & 0xFFFFF;
return new string(new []
{
V2[a % 26],
V2[a / 26],
V2[b % 26],
V2[b / 26 % 26],
V2[b / (26 * 26) % 26],
V2[b / (26 * 26 * 26) % 26]
});
}
public static int GameNameToInt(string code)
{
var upper = code.ToUpperInvariant();
if (upper.Any(x => !char.IsLetter(x)))
{
return -1;
}
var len = code.Length;
if (len == 6)
{
return GameNameToIntV2(upper);
}
if (len == 4)
{
return code[0] | ((code[1] | ((code[2] | (code[3] << 8)) << 8)) << 8);
}
return -1;
}
private static int GameNameToIntV2(string code)
{
var a = V2Map[code[0] - 65];
var b = V2Map[code[1] - 65];
var c = V2Map[code[2] - 65];
var d = V2Map[code[3] - 65];
var e = V2Map[code[4] - 65];
var f = V2Map[code[5] - 65];
var one = (a + 26 * b) & 0x3FF;
var two = (c + 26 * (d + 26 * (e + 26 * f)));
return (int) (one | ((two << 10) & 0x3FFFFC00) | 0x80000000);
}
public static int GenerateCode(int len)
{
if (len != 4 && len != 6)
{
throw new ArgumentException("should be 4 or 6", nameof(len));
}
// Generate random bytes.
#if NETSTANDARD2_0
var data = new byte[len];
#else
Span<byte> data = stackalloc byte[len];
#endif
Random.GetBytes(data);
// Convert to their char representation.
Span<char> dataChar = stackalloc char[len];
for (var i = 0; i < len; i++)
{
dataChar[i] = V2[V2Map[data[i] % 26]];
}
#if NETSTANDARD2_0
return GameNameToInt(new string(dataChar.ToArray()));
#else
return GameNameToInt(new string(dataChar));
#endif
}
}
}
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