Check if the clone target directory already exists.

And show a validation error if it doesn't. Fixes #360.

src/GitHub.App/ViewModels/RepositoryCloneViewModel.cs

@@ -3,8 +3,11 @@
 using System.ComponentModel.Composition;
 using System.Diagnostics;
 using System.Globalization;
+using System.IO;
+using System.Linq;
 using System.Reactive;
 using System.Reactive.Linq;
+using System.Text.RegularExpressions;
 using System.Windows.Input;
 using GitHub.App;
 using GitHub.Exports;
@@ -80,7 +83,17 @@ public RepositoryCloneViewModel(
                 signalReset: filterResetSignal
             );
 
-            BaseRepositoryPathValidator = this.CreateBaseRepositoryPathValidator();
+            var baseRepositoryPath = this.WhenAny(
+                x => x.BaseRepositoryPath,
+                x => x.SelectedRepository,
+                (x, y) => x.Value);
+
+            BaseRepositoryPathValidator = ReactivePropertyValidator.ForObservable(baseRepositoryPath)
+                .IfNullOrEmpty("Please enter a repository path")
+                .IfTrue(x => x.Length > 200, "Path too long")
+                .IfContainsInvalidPathChars("Path contains invalid characters")
+                .IfPathNotRooted("Please enter a valid path")
+                .IfTrue(IsAlreadyRepoAtPath, Resources.RepositoryNameValidatorAlreadyExists);
 
             var canCloneObservable = this.WhenAny(
                 x => x.SelectedRepository,
@@ -140,6 +153,35 @@ IObservable<Unit> OnCloneRepository(object state)
             });
         }
 
+        bool IsAlreadyRepoAtPath(string baseRepositoryPath)
+        {
+            bool isAlreadyRepoAtPath = false;
+
+            if (SelectedRepository != null)
+            {
+                var validationResult = BaseRepositoryPathValidator.ValidationResult;
+                if (validationResult != null && validationResult.IsValid)
+                {
+                    string potentialPath = Path.Combine(baseRepositoryPath, SelectedRepository.Name);
+                    isAlreadyRepoAtPath = IsGitRepo(potentialPath);
+                }
+            }
+
+            return isAlreadyRepoAtPath;
+        }
+
+        bool IsGitRepo(string path)
+        {
+            try
+            {
+                return operatingSystem.File.Exists(Path.Combine(path, ".git", "HEAD"));
+            }
+            catch (PathTooLongException)
+            {
+                return false;
+            }
+        }
+
         /// <summary>
         /// Path to clone repositories into
         /// </summary>

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

@@ -5,6 +5,7 @@
 using System.Threading.Tasks;
 using GitHub.Models;
 using GitHub.Services;
+using GitHub.Validation;
 using GitHub.ViewModels;
 using NSubstitute;
 using Rothko;
@@ -196,6 +197,33 @@ public void IsTrueIfLoadingReposFails()
         }
     }
 
+    public class TheBaseRepositoryPathValidator
+    {
+        [Fact]
+        public void IsInvalidWhenDestinationRepositoryExists()
+        {
+            var repo = Substitute.For<IRepositoryModel>();
+            repo.Name.Returns("bar");
+            var repositoryHost = Substitute.For<IRepositoryHost>();
+            repositoryHost.ModelService.GetRepositories().Returns(Observable.Return(new[] { repo }));
+            var cloneService = Substitute.For<IRepositoryCloneService>();
+            var os = Substitute.For<IOperatingSystem>();
+            var files = Substitute.For<IFileFacade>();
+            os.File.Returns(files);
+            files.Exists(@"c:\foo\bar\.git\HEAD").Returns(true);
+            var vm = new RepositoryCloneViewModel(
+                repositoryHost,
+                cloneService,
+                os,
+                Substitute.For<INotificationService>());
+
+            vm.BaseRepositoryPath = @"c:\foo";
+            vm.SelectedRepository = repo;
+
+            Assert.Equal(ValidationStatus.Invalid, vm.BaseRepositoryPathValidator.ValidationResult.Status);
+        }
+    }
+
     public class TheCloneCommand : TestBaseClass
     {
         [Fact]