Migrating blogger to Vuepress

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.Json;
using System.Text.RegularExpressions;
using ServiceStack;

namespace BloggerMigration
{
    class Program
    {
        private static string mdTemplate = @"---
title: {0}
date: {1}
{2}
---

{3}";

        static void Main(string[] args)
        {
            var initialResponse =
                "https://www.googleapis.com/blogger/v3/blogs/<YourBlogId>/posts?key=<APIKEY>"
                    .GetJsonFromUrl()
                    .FromJson<BloggerPostsResponse>();

            var posts = initialResponse.Items;

            while (initialResponse.NextPageToken != null)
            {
                initialResponse =
                    $"https://www.googleapis.com/blogger/v3/blogs/<YourBlogId>/posts?key=<APIKEY>&pageToken={initialResponse.NextPageToken}"
                        .GetJsonFromUrl()
                        .FromJson<BloggerPostsResponse>();

                posts.AddRange(initialResponse.Items);
            }

            var uniquePosts = posts.GroupBy(x => x.Id)
                .Select(x => x.First())
                .ToList();

            var converter = new ReverseMarkdown.Converter();
            foreach (var postItem in uniquePosts)
            {
                var imgDirName = postItem.Url.Split("/").Last().Replace(".html", "");
                var images = GetImageLinks(postItem.Content).Where(x => x.Contains("blogspot.com")).ToList();
                var imgDirPath = ($"..\\..\\..\\images\\archive\\{imgDirName}\\").MapAbsolutePath();

                foreach (var img in images)
                {
                    Directory.CreateDirectory(imgDirPath);
                    var scale = img.Split("/")[7];
                    var bytes = img.Replace($"/{scale}/", "/s10000/").GetBytesFromUrl();
                    var imgName = img.Split("/")[8];
                    File.WriteAllBytes((Path.Join(imgDirPath, imgName)).MapAbsolutePath(), bytes);
                    postItem.Content = postItem.Content.Replace(img, $"/images/archive/{imgDirName}/{imgName}");
                }

                // Update links
                var anchorLinks = GetAnchorLinks(postItem.Content)
                    .Where(x => x.Contains("blogspot.com"))
                    .ToList();

                foreach (var link in anchorLinks)
                {
                    var imgName = link.Split("/")[8];
                    postItem.Content = postItem.Content.Replace(link, $"/images/archive/{imgDirName}/{imgName}");
                }

                // HTML -> MarkDown
                postItem.Content = converter.Convert(postItem.Content);

                // Replace Gist embed scripts with code fence.
                var scripts = GetScriptUrls(postItem.Content)
                    .Where(x => x.Contains("gist.github.com"))
                    .ToList();

                foreach (var script in scripts)
                {
                    var url = script.Substring(0, script.Length - 3);
                    var gistId = url.Split("/").Last();
                    var gistJson = ("https://api.github.com/gists/" + gistId).GetJsonFromUrl(request =>
                    {
                        request.Headers.Add("User-Agent","Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:93.0) Gecko/20100101 Firefox/93.0");
                    });
                    var gistDoc = JsonDocument.Parse(gistJson);
                    GistFile gistFile = new GistFile();
                    foreach (var file in gistDoc.RootElement.GetProperty("files").EnumerateObject())
                    {
                        gistFile = file.Value.ToString().FromJson<GistFile>();
                    }

                    postItem.Content = postItem.Content.Replace($"<script src=\"{script}\"></script>", 
                        $@"
```
{gistFile.content}
```
");
                }

                // Write modified MD
                var tags = postItem.Labels != null ? "tags:\n- " + postItem.Labels.Join("\n- ") : "";
                var mdOutput = mdTemplate.Fmt(postItem.Title, postItem.Published.ToString("yyyy-MM-dd"),
                    tags,
                    postItem.Content);

                var fileName = postItem.Url.Split("/").Last().Replace(".html", ".md");

                File.WriteAllText(("..\\..\\..\\_archive\\" + fileName).MapAbsolutePath(), mdOutput);
            }
        }
        
        static IEnumerable<String> GetScriptUrls(String inputHTML)
        {
            const string pattern = @"<script\b[^\<\>]+?\bsrc\s*=\s*[""'](?<L>.+?)[""'][^\<\>]*?\>";

            foreach (Match match in Regex.Matches(inputHTML, pattern, RegexOptions.IgnoreCase))
            {
                var imageLink = match.Groups["L"].Value;
                yield return imageLink;
            }
        }

        static IEnumerable<String> GetImageLinks(String inputHTML)
        {
            const string pattern = @"<img\b[^\<\>]+?\bsrc\s*=\s*[""'](?<L>.+?)[""'][^\<\>]*?\>";

            foreach (Match match in Regex.Matches(inputHTML, pattern, RegexOptions.IgnoreCase))
            {
                var imageLink = match.Groups["L"].Value;
                yield return imageLink;
            }
        }

        static IEnumerable<String> GetAnchorLinks(String inputHTML)
        {
            const string pattern = @"<a\b[^\<\>]+?\bhref\s*=\s*[""'](?<L>.+?)[""'][^\<\>]*?\>";

            foreach (Match match in Regex.Matches(inputHTML, pattern, RegexOptions.IgnoreCase))
            {
                var anchorLinks = match.Groups["L"].Value;
                yield return anchorLinks;
            }
        }
    }

    public class BloggerPostsResponse
    {
        public string NextPageToken { get; set; }
        public List<PostItem> Items { get; set; }
    }

    public class PostItem
    {
        public string Id { get; set; }
        public DateTime Published { get; set; }
        public string Url { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }
        public List<string> Labels { get; set; }
    }

    public class GistFile
    {
        public string filename { get; set; }
        public string type { get; set; }
        public string content { get; set; }
        public string raw_url { get; set; }
    }
}