Trace the chain of redirects for a set of URLs

UrlRedirectTracer.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Xml.Linq;

namespace RedirectTracer
{
    class Program
    {
        private static readonly string _outputFile = "output.csv";

        static void Main()
        {
            var urls = GetURLs();

            File.WriteAllText(_outputFile, "Page,FinalTarget,FinalStatusCode,TotalRedirects,UrlChain\r\n");

            using (var client = new HttpClient(new HttpClientHandler { AllowAutoRedirect = false }))
            {
                foreach (var url in urls)
                {
                    var results = GetTarget(url, client).ToArray();
                    string data = BuildCSV(url, results);
                    File.AppendAllLines(_outputFile, new[] { data });
                    Console.WriteLine(data);
                }
            }
        }

        private static IEnumerable<UrlFrame> GetTarget(string url, HttpClient client)
        {
            var response = client.GetAsync(url).Result;
            yield return new UrlFrame
            {
                Url = response.RequestMessage.RequestUri.ToString(),
                StatusCode = (int)response.StatusCode
            };

            if ((int)response.StatusCode / 100 == 3)
            {
                var target = response.Headers.Location.IsAbsoluteUri
                    ? response.Headers.Location.ToString()
                    : new Uri(response.RequestMessage.RequestUri, response.Headers.Location.ToString()).ToString();

                foreach (var item in GetTarget(target, client))
                {
                    yield return item;
                }
            }
        }

        private static IEnumerable<string> GetURLs()
        {
            // TODO Return starting URLs
        }

        private static string BuildCSV(string url, UrlFrame[] results)
        {
            return $"{url}, {results.Last().Url},{results.Last().StatusCode},{results.Count() - 1},{string.Join(" => ", results.Select(f => $"{f.Url} {f.StatusCode}"))}";
        }

        private class UrlFrame
        {
            public string Url { get; set; }
            public int StatusCode { get; set; }
        }
    }
}