I was in need of a CopyFolder function for the FolderManager --- FolderManager.Instance.CopyFolder().

Not having found one, I wrote one. If this is useful, please feel free to use it. If you have any suggestions or modifications, let me know.

//Usage

     var sourceFolder = FolderManager.Instance.GetFolder(PortalId, "Assets/_default/");
     var rootDestFolder = FolderManager.Instance.GetFolder(PortalId, "Assets/");
     
     //Copy a folder to a different root folder with a new folder name
     FolderManager.Instance.CopyFolder(sourceFolder, rootDestFolder,"myNewFolderName");
     
     //copy a folder to the same root folder with a new foldername
     FolderManager.Instance.CopyFolder(sourceFolder, sourceFolder, "myNewFolderName");
     
     //copy a folder to a new destination within the same portal
     FolderManager.Instance.CopyFolder(PortalId, sourceFolder, "Assets/myNewFolderName/");

//Implementation

using System;
using System.IO;
using System.Linq;
using System.Web;
using DotNetNuke.Services.FileSystem;

namespace DNNExtensions
{
    public static class Extensions
    {
        /// <summary>
        /// Copy an existing folder and contents to the a new folder in the destination. After copying, the destination will
        /// contain a folder with the same name as the source folder.
        /// </summary>
        /// <param name="ifm"></param>
        /// <param name="source">An exising folder</param>
        /// <param name="rootDest">The parent folder into which the new folder will be created</param>
        public static void CopyFolder(this IFolderManager ifm, IFolderInfo source, IFolderInfo rootDest)
        {
            if (!ifm.FolderExists(rootDest.PortalID, rootDest.FolderPath+$"{source.FolderName}/"))
            {
                rootDest=  ifm.AddFolder(rootDest.PortalID, rootDest.FolderPath+$"{source.FolderName}/");
            }
            var diSource = source.PhysicalPath;
            var diDest = rootDest.PhysicalPath;
            _copyFolder(diSource,diDest,rootDest.PortalID);
            ifm.Synchronize(rootDest.PortalID,rootDest.FolderPath);
        }

        /// <summary>
        /// Copy an existing folder and contents to the a new folder in the destination. After copying, the destination will
        /// contain a folder with the specifed newFolderName.
        /// </summary>
        /// <param name="ifm"></param>
        /// <param name="source">An exising folder</param>
        /// <param name="rootDest">The parent folder info into which the new folder will be created</param>
        /// <param name="newFolderName">The name of the new folder</param>
        public static IFolderInfo CopyFolder(this IFolderManager ifm, IFolderInfo source, IFolderInfo rootDest, string newFolderName)
        {
            var newDest=!ifm.FolderExists(rootDest.PortalID, rootDest.FolderPath+newFolderName+"/")?ifm.AddFolder(rootDest.PortalID, rootDest.FolderPath+newFolderName+"/"):ifm.GetFolder(rootDest.PortalID, rootDest.FolderPath+newFolderName+"/");

            var diSource = source.PhysicalPath;
            var diDest = newDest.PhysicalPath;
            _copyFolder(diSource,diDest,newDest.PortalID);
            ifm.Synchronize(rootDest.PortalID,rootDest.FolderPath,true,true);
            return newDest;

        }
        /// <summary>
        /// Copy an existing folder and contents to a new folder using the destination path.
        /// </summary>
        /// <param name="ifm"></param>
        /// <param name="portalId">The portal for the new folder</param>
        /// <param name="source">An exising folder</param>
        /// <param name="destPath">The path and name of the new folder within the portal</param>
        public static IFolderInfo CopyFolder(this IFolderManager ifm, int portalId, IFolderInfo source, string destPath)
        {
            var newDest=!ifm.FolderExists(portalId, destPath)?ifm.AddFolder(portalId, destPath):ifm.GetFolder(portalId,destPath);
            var diSource=source.PhysicalPath;
            _copyFolder(diSource,newDest.PhysicalPath,portalId);
            ifm.Synchronize(portalId,newDest.FolderPath,true,true);
            return newDest;
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="ifm"></param>
        /// <param name="source"></param>
        /// <param name="dest"></param>
        /// <param name="recurse">Copy subfolders and files, too</param>
        /// <returns></returns>
        public static IFolderInfo CopyFiles(this IFileManager ifm, IFolderInfo source, IFolderInfo dest, Boolean recurse=false)
        {
            var diSource = new DirectoryInfo(source.PhysicalPath);
            var diDest = new DirectoryInfo(dest.PhysicalPath);
            _copyAll(diSource, diDest, recurse);
            return dest;
        }

        private static void _copyFolder(string sourceDirectory, string targetDirectory, int portalId)
        {
            DirectoryInfo diSource = new DirectoryInfo(sourceDirectory);
            DirectoryInfo diTarget = new DirectoryInfo(targetDirectory);

            _copyAll(diSource, diTarget);
           
        }

        private static void _copyAll(DirectoryInfo source, DirectoryInfo target, Boolean recurse=true)
        {
            var dirList = source.GetDirectories().Where(p=>p.FullName+@"\"!=target.FullName&&p.FullName!=target.FullName);
            // Copy each file into the new directory.
            foreach (System.IO.FileInfo fi in source.GetFiles())
            {
                fi.CopyTo(Path.Combine(target.FullName, fi.Name), true);
            }

            // Copy each subdirectory using recursion.
            if (!recurse) return;
            foreach (DirectoryInfo diSourceSubDir in dirList)
            {
                DirectoryInfo nextTargetSubDir =
                    target.CreateSubdirectory(diSourceSubDir.Name);
                _copyAll(diSourceSubDir, nextTargetSubDir);
            }
        }
    }
}

In space, no one can hear you scream? 

I'll take a look at it. I've never posted anything there.

Thanks!