EPLMetadataGenerator/Program.cs

using System.Net;
using System.Security.Cryptography;
using System.Text.Json;
using System.Text.Json.Nodes;
using System.Xml;

const string mavenMetadataUrl = "https://maven.ely.by/releases/by/ely/authlib/maven-metadata.xml";
const string authlibInjectorUrl =
    "https://github.com/yushijinhun/authlib-injector/releases/download/v1.2.5/authlib-injector-1.2.5.jar";

var client = new HttpClient();
var metadataXml = await client.GetStringAsync(mavenMetadataUrl);

var document = new XmlDocument();
document.LoadXml(metadataXml);

var versioning = document["metadata"]!["versioning"];
var versions = versioning!["versions"]!.GetElementsByTagName("version");

var versionsDict = new Dictionary<string, string>();
foreach (var versionObject in versions)
{
    var versionElement = versionObject as XmlElement;
    var fullVersion = versionElement!.InnerText;
    var authlibVersion = fullVersion.Split('-').First();
    if (versionsDict.TryGetValue(authlibVersion, out var existing))
    {
        var newElyPatchNumber = Convert.ToInt32(fullVersion.Split('.').Last());
        var existingElyPatchNumber = Convert.ToInt32(existing.Split('.').Last());
        if (newElyPatchNumber > existingElyPatchNumber)
        {
            versionsDict.Remove(authlibVersion);
        }
        else
        {
            continue;
        }
    }

    versionsDict.Add(authlibVersion, fullVersion);
}

versionsDict = versionsDict.OrderByDescending(kvp =>
{
    var versionNumbers = kvp.Key.Split('.');
    var score = 0;
    if (versionNumbers.Length > 0)
    {
        score += 1_000_000 * Convert.ToInt32(versionNumbers[0]);
    }
    if (versionNumbers.Length > 1)
    {
        score += 1_000 * Convert.ToInt32(versionNumbers[1]);
    }
    if (versionNumbers.Length > 2)
    {
        score += Convert.ToInt32(versionNumbers[2]);
    }

    return score;
}).ToDictionary();

var overrides = new JsonObject();
foreach (var version in versionsDict)
{
    // TODO: replace with GitHub repo
    var downloadUrl = $"https://llaun.ch/repo/libraries/by/ely/authlib/{version.Value}/authlib-{version.Value}.jar";
    byte[] result;
    try
    {
        result = await client.GetByteArrayAsync(downloadUrl);
    }
    catch (HttpRequestException e)
    {
        if (e.StatusCode != HttpStatusCode.NotFound) throw;
        continue;
    }

    var sha1 = Convert.ToHexStringLower(SHA1.HashData(result));
    var size = result.Length;
    overrides[version.Key] = new JsonObject
    {
        ["url"] = downloadUrl,
        ["sha1"] = sha1,
        ["size"] = size
    };
}

var root = new JsonObject
{
    ["overrides"] = new JsonObject
    {
        ["com.mojang:authlib"] = overrides
    },
    ["extras"] = new JsonObject
    {
        ["authlib-injector"] = authlibInjectorUrl
    }
};

await using var output = File.Create("epl_metadata.json");
await JsonSerializer.SerializeAsync(output, root, new JsonSerializerOptions { WriteIndented = true });