Use GitHub url for UpdateManager

src/Squirrel/Squirrel.csproj

@@ -78,6 +78,8 @@
     <Reference Include="System" />
     <Reference Include="System.Core" />
     <Reference Include="System.Drawing" />
+    <Reference Include="System.Net.Http" />
+    <Reference Include="System.Net.Http.Formatting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
     <Reference Include="System.Runtime.Serialization" />
     <Reference Include="System.Xml.Linq" />
     <Reference Include="Microsoft.CSharp" />
@@ -106,6 +108,7 @@
     <Compile Include="UpdateInfo.cs" />
     <Compile Include="UpdateManager.CheckForUpdates.cs" />
     <Compile Include="UpdateManager.cs" />
+    <Compile Include="UpdateManager.Factory.cs" />
     <Compile Include="Utility.cs" />
   </ItemGroup>
   <ItemGroup>

src/Squirrel/UpdateManager.Factory.cs

@@ -0,0 +1,65 @@
+using Splat;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Net.Http.Formatting;
+using System.Net.Http.Headers;
+using System.Reflection;
+using System.Runtime.Serialization;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Squirrel
+{
+    public sealed partial class UpdateManager
+    {
+        const string gitHubUrl = "https://api.github.com";
+
+        [DataContract]
+        public class Release
+        {
+            [DataMember(Name = "prerelease")]
+            public bool Prerelease { get; set; }
+
+            [DataMember(Name = "published_at")]
+            public DateTime PublishedAt { get; set; }
+
+            [DataMember(Name = "html_url")]
+            public string HtmlUrl { get; set; }
+        }
+
+        public static async Task<UpdateManager> GitHubUpdateManager(
+        string repoUrl,
+        string applicationName = null,
+        string rootDirectory = null,
+        IFileDownloader urlDownloader = null,
+        bool prerelease = false)
+        {
+            var repoUri = new Uri(repoUrl);
+            var userAgent = new ProductInfoHeaderValue("Squirrel", Assembly.GetExecutingAssembly().GetName().Version.ToString());
+
+            if (repoUri.Segments.Count() != 3)
+            {
+                throw new Exception("Repo URL must be to the root URL of the repo e.g. https://github.com/myuser/myrepo");
+            }
+
+            using (var client = new HttpClient() { BaseAddress = new Uri(gitHubUrl) })
+            {
+                client.DefaultRequestHeaders.UserAgent.Add(userAgent);
+                var response = await client.GetAsync(String.Format("/repos{0}/releases", repoUri.PathAndQuery));
+                response.EnsureSuccessStatusCode();
+
+                var releases = await response.Content.ReadAsAsync<IEnumerable<Release>>();
+                var latestRelease = releases
+                .Where(x => prerelease ? x.Prerelease : !x.Prerelease)
+                .OrderByDescending(x => x.PublishedAt)
+                .First();
+
+                var latestReleaseUrl = latestRelease.HtmlUrl.Replace("/tag/", "/download/");
+
+                return new UpdateManager(latestReleaseUrl, applicationName, rootDirectory, urlDownloader);
+            }
+        }
+    }
+}