private static SlnFolder GetRootFolder()

in src/Microsoft.VisualStudio.SlnGen/SlnHierarchy.cs [171:206]
30 lines of code
6 McCabe index (conditional complexity)

        private static SlnFolder GetRootFolder(IEnumerable<SlnProject> projects)
        {
            List<string> paths = projects.Where(i => !i.IsMainProject).Select(i => Directory.GetParent(i.FullPath).FullName).ToList();

            if (!paths.Any())
            {
                throw new InvalidOperationException();
            }

            // TODO: Unit tests, optimize
            string commonPath = string.Empty;

            List<string> separatedPath = paths
                .First(str => str.Length == paths.Max(st2 => st2.Length))
                .Split(new[] { Path.DirectorySeparatorChar })
                .ToList();

            string nextPath = null;
            foreach (string pathSegment in separatedPath.AsEnumerable())
            {
                if (commonPath.Length == 0 && paths.All(str => str.StartsWith(pathSegment, StringComparison.OrdinalIgnoreCase)))
                {
                    commonPath = pathSegment + Path.DirectorySeparatorChar;
                }
                else if (paths.All(str => str.StartsWith(nextPath = $"{commonPath}{pathSegment}{Path.DirectorySeparatorChar}", StringComparison.OrdinalIgnoreCase)))
                {
                    commonPath = nextPath;
                }
                else
                {
                    break;
                }
            }

            return new SlnFolder(commonPath.TrimEnd(Path.DirectorySeparatorChar));
        }