Convert IFileInfo to FileInfo or DirectoryInfo objects.

FileProviderConvertersExtensions.cs

using System;
using System.IO;

using Microsoft.Extensions.FileProviders;

// ReSharper disable once CheckNamespace
namespace kwd.gist
{
    /// <summary>
    /// Extensions to convert <see cref="IFileInfo"/> to
    /// <see cref="FileInfo"/> and <see cref="DirectoryInfo"/> objects.
    /// </summary>
    public static class FileProviderConvertersExtensions
    {
        /// <summary>
        /// Convert <see cref="IFileInfo"/> to <see cref="DirectoryInfo"/>
        /// </summary>
        /// <exception cref="NotPhysicalFile"></exception>
        /// <exception cref="IsFile"></exception>
        public static DirectoryInfo AsDirectory(this IFileInfo fileInfo)
        {
            if (fileInfo.PhysicalPath == null) { throw new NotPhysicalFile(); }
            if (File.Exists(fileInfo.PhysicalPath)) { throw new IsDirectory(); }

            return new DirectoryInfo(fileInfo.PhysicalPath);
        }

        /// <summary>
        /// Try convert <see cref="IFileInfo"/> to <see cref="DirectoryInfo"/>.
        /// </summary>
        /// <returns>
        /// <see cref="DirectoryInfo"/> or null.
        /// </returns>
        public static DirectoryInfo TryAsDirectory(this IFileInfo file)
            => file.PhysicalPath == null ||
               File.Exists(file.PhysicalPath) ? null : new DirectoryInfo(file.PhysicalPath);

        /// <summary>
        /// Convert <see cref="IFileInfo"/> to <see cref="FileInfo"/>
        /// </summary>
        /// <exception cref="NotPhysicalFile"></exception>
        /// <exception cref="IsDirectory"></exception>
        public static FileInfo AsFile(this IFileInfo file)
        {
            if (file.PhysicalPath == null) { throw new NotPhysicalFile(); }
            if (Directory.Exists(file.PhysicalPath)) { throw new IsFile(); }

            return new FileInfo(file.PhysicalPath);
        }

        /// <summary>
        /// Try convert <see cref="IFileInfo"/> to a <see cref="FileInfo"/>
        /// </summary>
        /// <returns>
        /// <see cref="FileInfo"/> or null;
        /// </returns>
        public static FileInfo TryAsFile(this IFileInfo file) =>
            file.PhysicalPath == null ||
            Directory.Exists(file.PhysicalPath) ? null : new FileInfo(file.PhysicalPath);
    }

    public class NotPhysicalFile : Exception { }
    public class IsDirectory : Exception { }
    public class IsFile : Exception { }
}