Converts Blogger export XML and converts to Markdown

BloggerToMarkdown.cs

// Requires nuget Package https://www.nuget.org/packages/Html2Markdown/

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml;
using Html2Markdown;

namespace BloggerToMd
{
    public static class BloggerToMarkdown
    {
        public static void Convert(string bloggerFileName)
        {
            var document = Load(bloggerFileName);
            var manager = BloggerNameSpaceManager(document);
            var blogPosts = document.DocumentElement.SelectNodes("atom:entry[contains(atom:id, 'post')]", manager);

            var folder = Path.GetDirectoryName(bloggerFileName);
            foreach (XmlNode blogPost in blogPosts)
            {
                var post = ToBlogPost(blogPost, manager);
                SaveToFile(post, folder);
            }
        }

        private static XmlDocument Load(string bloggerFileName)
        {
            var doc = new XmlDocument();
            doc.Load(bloggerFileName);
            return doc;
        }

        private static XmlNamespaceManager BloggerNameSpaceManager(XmlDocument bloggerDocument)
        {
            var manager = new XmlNamespaceManager(bloggerDocument.NameTable);
            manager.AddNamespace("openSearch", "http://a9.com/-/spec/opensearchrss/1.0/");
            manager.AddNamespace("gd", "http://schemas.google.com/g/2005");
            manager.AddNamespace("thr", "http://purl.org/syndication/thread/1.0");
            manager.AddNamespace("georss", "http://www.georss.org/georss");
            manager.AddNamespace("atom", "http://www.w3.org/2005/Atom");
            return manager;
        }

        private static BlogPost ToBlogPost(XmlNode blogPost, XmlNamespaceManager manager)
        {
            var converter = new Converter();
            var title = blogPost.SelectSingleNode("atom:title", manager).InnerText;
            var date = DateTimeOffset.Parse(blogPost.SelectSingleNode("atom:published", manager).InnerText);
            var tagNodes = blogPost.SelectNodes("atom:category[@scheme='http://www.blogger.com/atom/ns#']/@term",
                manager);

            var tags = new List<string>();
            foreach (XmlNode tag in tagNodes)
            {
                tags.Add(tag.Value);
            }

            var content = blogPost.SelectSingleNode("atom:content", manager).InnerText;
            var markdown = converter.Convert(content);

            return new BlogPost(title, date, tags.ToArray(), markdown);
        }

        private static void SaveToFile(BlogPost post, string folder)
        {
            var fileName = $"{post.Date:yyyy-MM-dd}-{SafeFileName(post.Title)}.md";
            var sb = new StringBuilder();
            sb.Append($@"Title: {post.Title}
Date: {post.Date:dd/MM/yy}
---
");
            sb.Append(post.Markdown);

            var fullPath = Path.Combine(folder, fileName);
            File.WriteAllText(fullPath, sb.ToString());
        }

        private static string SafeFileName(string fileName) =>
            Path.GetInvalidFileNameChars()
                .Aggregate(fileName, (current, c) => current.Replace(c, '-'))
                .Substring(0,10);

        private class BlogPost
        {
            public BlogPost(string title, DateTimeOffset date, string[] tags, string markdown)
            {
                Title = title;
                Date = date;
                Tags = tags;
                Markdown = markdown;
            }

            public string Title { get; }
            public DateTimeOffset Date { get; }
            public string[] Tags { get; }
            public string Markdown { get; }
        }
    }
}