using System;

using System.Text;

using System.Buffers;

​

public class Program

{

    static void Main(string[] args)

    {

        byte[] data = { 64, 98, 97, 100, 103, 101, 45, 105, 110, 102, 111, 61, 115, 117, 98, 115, 99, 114, 105, 98, 101, 114, 47, 55, 59, 98, 97, 100, 103, 101, 115, 61, 115, 117, 98, 115, 99, 114, 105, 98, 101, 114, 47, 54, 44, 110, 111, 95, 118, 105, 100, 101, 111, 47, 49, 59, 99, 111, 108, 111, 114, 61, 35, 70, 70, 48, 48, 48, 48, 59, 100, 105, 115, 112, 108, 97, 121, 45, 110, 97, 109, 101, 61, 110, 101, 114, 105, 120, 121, 122, 59, 101, 109, 111, 116, 101, 115, 61, 59, 102, 105, 114, 115, 116, 45, 109, 115, 103, 61, 48, 59, 102, 108, 97, 103, 115, 61, 59, 105, 100, 61, 50, 102, 52, 100, 56, 57, 98, 101, 45, 56, 102, 50, 52, 45, 52, 50, 52, 52, 45, 98, 54, 102, 100, 45, 57, 98, 50, 51, 55, 48, 100, 54, 53, 57, 52, 98, 59, 109, 111, 100, 61, 48, 59, 114, 101, 112, 108, 121, 45, 112, 97, 114, 101, 110, 116, 45, 100, 105, 115, 112, 108, 97, 121, 45, 110, 97, 109, 101, 61, 110, 101, 114, 105, 120, 121, 122, 59, 114, 101, 112, 108, 121, 45, 112, 97, 114, 101, 110, 116, 45, 109, 115, 103, 45, 98, 111, 100, 121, 61, 45, 116, 97, 103, 115, 115, 97, 98, 99, 58, 97, 61, 54, 58, 102, 111, 111, 58, 64, 102, 111, 114, 115, 101, 110, 58, 120, 100, 59, 114, 101, 112, 108, 121, 45, 112, 97, 114, 101, 110, 116, 45, 109, 115, 103, 45, 105, 100, 61, 52, 100, 54, 98, 57, 54, 102, 52, 45, 100, 98, 102, 51, 45, 52, 100, 50, 53, 45, 97, 49, 49, 52, 45, 53, 48, 97, 98, 54, 55, 100, 101, 51, 52, 49, 50, 59, 114, 101, 112, 108, 121, 45, 112, 97, 114, 101, 110, 116, 45, 117, 115, 101, 114, 45, 105, 100, 61, 49, 50, 57, 53, 52, 54, 52, 53, 51, 59, 114, 101, 112, 108, 121, 45, 112, 97, 114, 101, 110, 116, 45, 117, 115, 101, 114, 45, 108, 111, 103, 105, 110, 61, 110, 101, 114, 105, 120, 121, 122, 59, 114, 101, 116, 117, 114, 110, 105, 110, 103, 45, 99, 104, 97, 116, 116, 101, 114, 61, 48, 59, 114, 111, 111, 109, 45, 105, 100, 61, 49, 49, 49, 52, 56, 56, 49, 55, 59, 115, 117, 98, 115, 99, 114, 105, 98, 101, 114, 61, 49, 59, 116, 109, 105, 45, 115, 101, 110, 116, 45, 116, 115, 61, 49, 54, 55, 51, 54, 57, 49, 48, 56, 54, 57, 54, 48, 59, 116, 117, 114, 98, 111, 61, 48, 59, 117, 115, 101, 114, 45, 105, 100, 61, 49, 50, 57, 53, 52, 54, 52, 53, 51, 59, 117, 115, 101, 114, 45, 116, 121, 112, 101, 61, 32, 58, 110, 101, 114, 105, 120, 121, 122, 33, 110, 101, 114, 105, 120, 121, 122, 64, 110, 101, 114, 105, 120, 121, 122, 46, 116, 109, 105, 46, 116, 119, 105, 116, 99, 104, 46, 116, 118, 32, 80, 82, 73, 86, 77, 83, 71, 32, 35, 112, 97, 106, 108, 97, 100, 97, 32, 58, 64, 110, 101, 114, 105, 120, 121, 122, 32, 97 };

        ReadOnlyMemory<byte> memory = new(data);

        var tags = ParseTags(memory);

        foreach (var kv in tags) {

            Console.WriteLine($"{Encoding.UTF8.GetString(kv.Key.Span)}: {Encoding.UTF8.GetString(kv.Value.Span)}");

        }

    }

​

    internal static IrcTag[] ParseTags(ReadOnlyMemory<byte> memory)

    {

        ReadOnlySpan<byte> span = memory.Span;

​

        const byte at = (byte)'@';

        const byte space = (byte)' ';

        const byte colon = (byte)':';

        const byte semiColon = (byte)';';

        const byte equals = (byte)'=';

​

        int tagsStartIndex = (span[0] == at || span[0] == colon) ? 1 : 0;

        int tagsEndIndex = span.IndexOf(space);

        int tagCount = 0;

​

        int tagIndex = 1;

        var tagIndexCountSpan = span;

        while ((tagIndex = tagIndexCountSpan.IndexOf(equals)) != -1) {

            tagCount++;

            tagIndexCountSpan = tagIndexCountSpan[(tagIndex+1)..];

        }

​

        IrcTag[] tags = ArrayPool<IrcTag>.Shared.Rent(tagCount); // When is this freed?

        int tagStart = tagsStartIndex;

        int tagEquals = 0;

        int tagEnd = 0;

​

        for (int x = 0;x < tagCount;x++) {

            if (tagStart >= tagsEndIndex) break;

​

            tagEquals = span[tagStart..].IndexOf(equals) + tagStart;

            if (tagEquals == tagStart - 1) break;

​

            tagEnd = span[tagEquals..].IndexOf(semiColon) + tagEquals;

            if (tagEnd == tagEquals - 1)

                tagEnd = tagsEndIndex;

​

            tags[x] = new IrcTag(memory[tagStart..tagEquals], memory[(tagEquals + 1)..tagEnd]);

​

            tagStart = tagEnd + 1;

        }

​

        return tags;

    }

​

    public readonly record struct IrcTag(ReadOnlyMemory<byte> Key, ReadOnlyMemory<byte> Value);

​

}