YouTube-like GUID

It's not a GUID

Let me jump in with the following

It uses the TotalMilliseconds from EPOCH and a valid set of characters.

This will not be globally unique but unique to the instance where it's defines

public string YoutubeLikeId()
{
    Thread.Sleep(1);//make everything unique while looping
    long ticks = (long)(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1,0,0,0,0))).TotalMilliseconds;//EPOCH
    char[] baseChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".ToCharArray();
    
    int i = 32;
    char[] buffer = new char[i];
    int targetBase= baseChars.Length;

    do
    {
        buffer[--i] = baseChars[ticks % targetBase];
        ticks = ticks / targetBase;
    }
    while (ticks > 0);

    char[] result = new char[32 - i];
    Array.Copy(buffer, i, result, 0, 32 - i);

    return new string(result);
}

The output will come something like

XOTgBsu
XOTgBtB
XOTgBtR
XOTgBtg
XOTgBtw
XOTgBuE

Update: The same can be achieved from Guid as

var guid = Guid.NewGuid(); 
guid.ToString("N");
guid.ToString("N").Substring(0,8);
guid.ToString("N").Substring(8,4);
guid.ToString("N").Substring(12,4);
guid.ToString("N").Substring(16,4);
guid.ToString("N").Substring(20,12);

For a Guid ecd65132-ab5a-4587-87b8-b875e2fe0f35 it will break it down in chunks as ecd65132 ,ab5a , 4587,87b8,b875e2fe0f35

but i can't guarantee it to be unique always.

Update 2: There is also a project called ShortGuid to get a url friendly GUID it can be converted fron/to a regular Guid

It works by encoding the Guid to Base64 as the code below

public static string Encode(Guid guid)
{
    string encoded = Convert.ToBase64String(guid.ToByteArray());

    encoded = encoded
        .Replace("/", "_")
        .Replace("+", "-");
    return encoded.Substring(0, 22);
}

The good thing about it it can be decoded again to get the Guid back with

public static Guid Decode(string value)
{
    // avoid parsing larger strings/blobs
    if (value.Length != 22)
    {
        throw new ArgumentException("A ShortGuid must be exactly 22 characters long. Receive a character string.");
    }

    string base64 = value
        .Replace("_", "/")
        .Replace("-", "+") + "==";

    byte[] blob = Convert.FromBase64String(base64);
    var guid = new Guid(blob);

    var sanityCheck = Encode(guid);
    if (sanityCheck != value)
    {
        throw new FormatException(
            @"Invalid strict ShortGuid encoded string. The string '{value}' is valid URL-safe Base64, " +
            @"but failed a round-trip test expecting '{sanityCheck}'."
        );
    }

    return guid;
}

So a Guid 4039124b-6153-4721-84dc-f56f5b057ac2 will be encoded as SxI5QFNhIUeE3PVvWwV6wg and the Output will look something like.

ANf-MxRHHky2TptaXBxcwA
zpjp-stmVE6ZCbOjbeyzew
jk7P-XYFokmqgGguk_530A
81t6YZtkikGfLglibYkDhQ
qiM2GmqCK0e8wQvOSn-zLA

Maybe using NanoId will save you from a lot of headaches: https://github.com/codeyu/nanoid-net

You can do something like:

var id = Nanoid.Generate('1234567890abcdef', 10) //=> "4f90d13a42"

And you can check the collision probability here: https://alex7kom.github.io/nano-nanoid-cc/