Make GitReferenceModel immutable.

To try and minimize the chances of null exceptions.

Author: grokys

src/GitHub.App/Services/ModelService.cs

@@ -354,6 +354,11 @@ IRemoteRepositoryModel Create(RepositoryCacheItem item)
             };
         }
 
+        private GitReferenceModel Create(GitReferenceCacheItem item)
+        {
+            return item != null ? new GitReferenceModel(item.Ref, item.Label, item.RepositoryCloneUrl) : null;
+        }
+
         IPullRequestModel Create(PullRequestCacheItem prCacheItem)
         {
             return new PullRequestModel(
@@ -364,13 +369,13 @@ IPullRequestModel Create(PullRequestCacheItem prCacheItem)
                 prCacheItem.UpdatedAt)
             {
                 Assignee = prCacheItem.Assignee != null ? Create(prCacheItem.Assignee) : null,
-                Base = prCacheItem.Base ?? new GitReferenceModel(),
+                Base = Create(prCacheItem.Base),
                 Body = prCacheItem.Body ?? string.Empty,
                 ChangedFiles = prCacheItem.ChangedFiles.Select(x => (IPullRequestFileModel)new PullRequestFileModel(x.FileName, x.Status)).ToList(),
                 CommentCount = prCacheItem.CommentCount,
                 CommitCount = prCacheItem.CommitCount,
                 CreatedAt = prCacheItem.CreatedAt,
-                Head = prCacheItem.Head,
+                Head = Create(prCacheItem.Head),
                 State = prCacheItem.State.HasValue ? 
                     prCacheItem.State.Value : 
                     prCacheItem.IsOpen.Value ? PullRequestStateEnum.Open : PullRequestStateEnum.Closed,                
@@ -475,10 +480,8 @@ public PullRequestCacheItem(PullRequest pr, IReadOnlyList<PullRequestFile> files
             {
                 Title = pr.Title;
                 Number = pr.Number;
-                Base = new GitReferenceModel { Label = pr.Base.Label, Ref = pr.Base.Ref, RepositoryCloneUrl = pr.Base.Repository.CloneUrl };
-                Head = pr.Head != null ?
-                    new GitReferenceModel { Label = pr.Head.Label, Ref = pr.Head.Ref, RepositoryCloneUrl = pr.Head.Repository.CloneUrl } :
-                    null;
+                Base = new GitReferenceCacheItem { Label = pr.Base.Label, Ref = pr.Base.Ref, RepositoryCloneUrl = pr.Base.Repository.CloneUrl };
+                Head = pr.Head != null ? new GitReferenceCacheItem { Label = pr.Head.Label, Ref = pr.Head.Ref, RepositoryCloneUrl = pr.Head.Repository.CloneUrl } : null;
                 CommentCount = pr.Comments + pr.ReviewComments;
                 CommitCount = pr.Commits;
                 Author = new AccountCacheItem(pr.User);
@@ -496,8 +499,8 @@ public PullRequestCacheItem(PullRequest pr, IReadOnlyList<PullRequestFile> files
 
             public string Title {get; set; }
             public int Number { get; set; }
-            public GitReferenceModel Base { get; set; }
-            public GitReferenceModel Head { get; set; }
+            public GitReferenceCacheItem Base { get; set; }
+            public GitReferenceCacheItem Head { get; set; }
             public int CommentCount { get; set; }
             public int CommitCount { get; set; }
             public AccountCacheItem Author { get; set; }
@@ -531,6 +534,7 @@ static PullRequestStateEnum GetState(PullRequest pullRequest)
             }
         }
 
+        [NullGuard(ValidationFlags.None)]
         public class PullRequestFileCacheItem
         {
             public PullRequestFileCacheItem()
@@ -546,5 +550,13 @@ public PullRequestFileCacheItem(PullRequestFile file)
             public string FileName { get; set; }
             public PullRequestFileStatus Status { get; set; }
         }
+
+        [NullGuard(ValidationFlags.None)]
+        public class GitReferenceCacheItem
+        {
+            public string Ref { get; set; }
+            public string Label { get; set; }
+            public string RepositoryCloneUrl { get; set; }
+        }
     }
 }

src/GitHub.Exports/Models/GitReferenceModel.cs

@@ -1,11 +1,29 @@
-using GitHub.Primitives;
+using GitHub.Extensions;
+using GitHub.Primitives;
 
 namespace GitHub.Models
 {
     public class GitReferenceModel
     {
-        public string Ref { get; set; }
-        public string Label { get; set; }
-        public UriString RepositoryCloneUrl { get; set; }
+        public GitReferenceModel(string @ref, string label, string repositoryCloneUri)
+            : this(@ref, label, new UriString(repositoryCloneUri))
+        {
+        }
+
+        public GitReferenceModel(string @ref, string label, UriString repositoryCloneUri)
+        {
+            Guard.ArgumentNotEmptyString(@ref, nameof(@ref));
+            Guard.ArgumentNotEmptyString(label, nameof(label));
+            Guard.ArgumentNotNull(repositoryCloneUri, nameof(repositoryCloneUri));
+            Guard.ArgumentNotEmptyString(repositoryCloneUri.ToString(), nameof(repositoryCloneUri));
+
+            Ref = @ref;
+            Label = label;
+            RepositoryCloneUrl = repositoryCloneUri;
+        }
+
+        public string Ref { get; }
+        public string Label { get; }
+        public UriString RepositoryCloneUrl { get; }
     }
 }

src/UnitTests/GitHub.App/Services/PullRequestServiceTests.cs

@@ -158,8 +158,8 @@ static IPullRequestModel CreatePullRequest()
             {
                 State = PullRequestStateEnum.Open,
                 Body = string.Empty,
-                Head = new GitReferenceModel { Label = "foo:baz", Ref = "source", RepositoryCloneUrl = "https://github.com/foo/bar.git" },
-                Base = new GitReferenceModel { Label = "foo:bar", Ref = "source", RepositoryCloneUrl = "https://github.com/foo/bar.git" },
+                Head = new GitReferenceModel("source", "foo:baz", "https://github.com/foo/bar.git"),
+                Base = new GitReferenceModel("dest", "foo:bar", "https://github.com/foo/bar.git"),
             };
         }
 

src/UnitTests/GitHub.App/ViewModels/PullRequestDetailViewModelTests.cs

@@ -368,8 +368,8 @@ PullRequestModel CreatePullRequest(string body = "PR Body")
             {
                 State = PullRequestStateEnum.Open,
                 Body = string.Empty,
-                Head = new GitReferenceModel { Label = "foo:baz", Ref = "source", RepositoryCloneUrl = "https://github.com/foo/bar.git" },
-                Base = new GitReferenceModel { Label = "foo:bar", Ref = "source", RepositoryCloneUrl = "https://github.com/foo/bar.git" },
+                Head = new GitReferenceModel("source", "foo:baz", "https://github.com/foo/bar.git"),
+                Base = new GitReferenceModel("dest", "foo:bar", "https://github.com/foo/bar.git"),
             };
         }
     }

src/UnitTests/Helpers/TestBaseClass.cs

@@ -58,7 +58,13 @@ protected static PullRequest CreatePullRequest(User user, int id, ItemState stat
         DateTimeOffset createdAt, DateTimeOffset updatedAt, int commentCount = 0, int reviewCommentCount = 0)
     {
         var uri = new Uri("https://url");
-        var repo = new Repository();
+        var uris = uri.ToString();
+        var repo = new Repository(uris, uris, uris, uris, uris, uris, uris,
+            1, user, "Repo", "Repo", string.Empty, string.Empty, string.Empty,
+            false, false, 0, 0, "master",
+            0, null, createdAt, updatedAt,
+            null, null, null,
+            false, false, false);
         return new PullRequest(uri, uri, uri, uri, uri, uri,
             id, state, title, "", createdAt, updatedAt,
             null, null,