gregExtractor/Utils/SteamLocator.cs

using Microsoft.Win32;
using System.Runtime.Versioning;

namespace gregExtractor.Utils;

public static class SteamLocator
{
    private const string DataCenterFolderName = "Data Center";

    public static string? FindGamePath()
    {
        foreach (string libraryRoot in EnumerateSteamLibraryRoots())
        {
            string candidate = Path.Combine(libraryRoot, "steamapps", "common", DataCenterFolderName);
            if (Directory.Exists(candidate))
                return candidate;
        }

        return null;
    }

    public static string? FindIl2CppAssembliesPath()
    {
        string? gamePath = FindGamePath();
        if (string.IsNullOrWhiteSpace(gamePath))
            return null;

        string modernPath = Path.Combine(gamePath, "MelonLoader", "Il2CppAssemblies");
        if (Directory.Exists(modernPath))
            return modernPath;

        string legacyPath = Path.Combine(gamePath, "MelonLoader", "Managed");
        if (Directory.Exists(legacyPath))
            return legacyPath;

        return null;
    }

    private static IEnumerable<string> EnumerateSteamLibraryRoots()
    {
        var roots = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        foreach (string installPath in ReadSteamInstallPaths())
        {
            if (string.IsNullOrWhiteSpace(installPath) || !Directory.Exists(installPath))
                continue;

            roots.Add(installPath);

            string libraryFile = Path.Combine(installPath, "steamapps", "libraryfolders.vdf");
            if (!File.Exists(libraryFile))
                continue;

            string content = File.ReadAllText(libraryFile);
            foreach (Match match in Regex.Matches(content, "\"path\"\\s+\"([^\"]+)\"", RegexOptions.IgnoreCase))
            {
                string parsedPath = match.Groups[1].Value.Replace("\\\\", "\\");
                if (!string.IsNullOrWhiteSpace(parsedPath) && Directory.Exists(parsedPath))
                    roots.Add(parsedPath);
            }
        }

        return roots;
    }

    private static IEnumerable<string> ReadSteamInstallPaths()
    {
        if (!OperatingSystem.IsWindows())
            return Enumerable.Empty<string>();

        var paths = new List<string>();

        string? wowPath = ReadRegistryValue(@"SOFTWARE\WOW6432Node\Valve\Steam", "InstallPath");
        if (!string.IsNullOrWhiteSpace(wowPath))
            paths.Add(wowPath);

        string? nativePath = ReadRegistryValue(@"SOFTWARE\Valve\Steam", "InstallPath");
        if (!string.IsNullOrWhiteSpace(nativePath))
            paths.Add(nativePath);

        return paths;
    }

    private static string? ReadRegistryValue(string keyPath, string valueName)
    {
        if (!OperatingSystem.IsWindows())
            return null;

        return ReadRegistryValueWindows(keyPath, valueName);
    }

    [SupportedOSPlatform("windows")]
    private static string? ReadRegistryValueWindows(string keyPath, string valueName)
    {
        try
        {
            using RegistryKey? key = Registry.LocalMachine.OpenSubKey(keyPath);
            return key?.GetValue(valueName) as string;
        }
        catch
        {
            return null;
        }
    }
}