NugetConfigReader.cs

using System;
using System.IO;
using System.Linq;
using System.Xml;
using System.Xml.Linq;

public static class NugetConfigReader
{

    public static string GetPackagesPathFromConfig(string currentDirectory)
    {
        while (true)
        {
            var packagePath = GetPackagePath(Path.Combine(currentDirectory, "nuget.config"));
            if (packagePath != null)
            {
                return packagePath;
            }
            packagePath = GetPackagePath(Path.Combine(currentDirectory, ".nuget", "nuget.config"));
            if (packagePath != null)
            {
                return packagePath;
            }
            try
            {
                var directoryInfo = Directory.GetParent(currentDirectory);
                if (directoryInfo == null)
                {
                    return null;
                }
                currentDirectory = directoryInfo.FullName;
            }
            catch
            {
                // trouble with tree walk. ignore
                return null;
            }
        }
    }

    public static string GetPackagePath(string nugetConfigPath)
    {
        var packagePath = Inner(nugetConfigPath);
        if (packagePath == null)
        {
            return null;
        }

        return Path.GetFullPath(packagePath);
    }

    static string Inner(string nugetConfigPath)
    {
        if (!File.Exists(nugetConfigPath))
        {
            return null;
        }

        XDocument xDocument;
        try
        {
            xDocument = XDocument.Load(nugetConfigPath);
        }
        catch (XmlException)
        {
            return null;
        }

        var repositoryPath = xDocument.Descendants("repositoryPath")
            .Select(x => x.Value)
            .FirstOrDefault(x => !string.IsNullOrWhiteSpace(x));
        if (repositoryPath != null)
        {
            return Path.Combine(Path.GetDirectoryName(nugetConfigPath), repositoryPath);
        }

        repositoryPath = xDocument.Descendants("add")
            .Where(x => string.Equals((string) x.Attribute("key"), "repositoryPath", StringComparison.OrdinalIgnoreCase))
            .Select(x => x.Attribute("value"))
            .Where(x => x != null)
            .Select(x => x.Value)
            .FirstOrDefault();
        if (repositoryPath == null)
        {
            return null;
        }

        if (repositoryPath.StartsWith("$\\"))
        {
            return repositoryPath.Replace("$", Path.Combine(Path.GetDirectoryName(nugetConfigPath)));
        }

        return Path.Combine(Path.GetDirectoryName(nugetConfigPath), repositoryPath);
    }
}