Add checkout command

git tfs checkout changesetId [-b=branch_name]
ex: git-tfs checkout 2365
      git-tfs checkout 2365 -b=bugfix_2365

Solve git-tfs#563

GitTfs/Commands/Checkout.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.IO;
+using NDesk.Options;
+using Sep.Git.Tfs.Core;
+using StructureMap;
+
+namespace Sep.Git.Tfs.Commands
+{
+    [Pluggable("checkout")]
+    [RequiresValidGitRepository]
+    [Description("checkout changesetId [-b=branch_name]\n   ex: git-tfs checkout 2365\n       git-tfs checkout 2365 -b=bugfix_2365\n")]
+    public class Checkout : GitTfsCommand
+    {
+        private readonly Globals _globals;
+        private readonly TextWriter _stdout;
+
+        public Checkout(Globals globals, TextWriter stdout)
+        {
+            _globals = globals;
+            _stdout = stdout;
+        }
+
+        public OptionSet OptionSet
+        {
+            get
+            {
+                return new OptionSet
+                {
+                    { "b|branch=", "Name of the branch to create", v => BranchName = v },
+                };
+            }
+        }
+
+        protected string BranchName { get; set; }
+
+        public int Run(string id)
+        {
+            long changesetId;
+            if(!long.TryParse(id, out changesetId))
+                throw new GitTfsException("error: wrong format for changeset id...");
+            var sha = _globals.Repository.FindCommitHashByChangesetId(changesetId);
+            if (string.IsNullOrEmpty(sha))
+                throw new GitTfsException("error: commit not found for this changeset id...");
+            string commitishToCheckout = sha;
+            if (!string.IsNullOrEmpty(BranchName))
+            {
+                BranchName = _globals.Repository.AssertValidBranchName(BranchName);
+                if(!_globals.Repository.CreateBranch(BranchName.ToLocalGitRef(), sha))
+                    throw new GitTfsException("error: can not create branch '" + BranchName + "'");
+                _stdout.WriteLine("Branch '" + BranchName + "' created...");
+                commitishToCheckout = BranchName;
+            }
+            if(!_globals.Repository.Checkout(commitishToCheckout))
+                throw new GitTfsException("error: unable to checkout '" + commitishToCheckout + "' due to changes in your workspace!",
+                    new List<string> { "commit or stash your changes before retrying..."});
+            return GitTfsExitCodes.OK;
+        }
+    }
+}

GitTfs/Commands/Init.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
@@ -171,5 +171,11 @@ public static string ToGitBranchNameFromTfsRepositoryPath(this string tfsReposit
                 : tfsRepositoryPath;
             return gitBranchNameExpected.ToGitRefName();
         }
+
+        public static string ToLocalGitRef(this string refName)
+        {
+            return "refs/heads/" + refName;
+        }
+
     }
 }

GitTfs/Commands/InitBranch.cs

@@ -380,7 +380,7 @@ private IFetchResult FetchRemote(IGitTfsRemote tfsRemote, bool stopOnFailMergeCo
                 if (fetchResult.IsSuccess && createBranch && tfsRemote.Id != GitTfsConstants.DefaultRepositoryId)
                 {
                     Trace.WriteLine("Try creating the local branch...");
-                    var branchRef = "refs/heads/" + tfsRemote.Id;
+                    var branchRef = tfsRemote.Id.ToLocalGitRef();
                     if (!_globals.Repository.HasRef(branchRef))
                     {
                         if (!_globals.Repository.CreateBranch(branchRef, tfsRemote.MaxCommitHash))

GitTfs/Core/GitRepository.cs

@@ -619,5 +619,18 @@ public void GarbageCollect(bool auto, string additionalMessage)
                 realStdout.WriteLine("Warning: `git gc` failed! " + additionalMessage);
             }
         }
+
+        public bool Checkout(string commitish)
+        {
+            try
+            {
+                _repository.Checkout(commitish);
+                return true;
+            }
+            catch (MergeConflictException ex)
+            {
+                return false;
+            }
+        }
     }
 }

GitTfs/Core/IGitRepository.cs

@@ -51,5 +51,6 @@ public interface IGitRepository : IGitHelpers
         void ResetRemote(IGitTfsRemote remoteToReset, string target);
         string GetCurrentBranch();
         void GarbageCollect(bool auto = false, string additionalMessage = null);
+        bool Checkout(string commitish);
     }
 }

GitTfs/GitTfs.csproj

@@ -97,6 +97,7 @@
     <Compile Include="..\Version.cs">
       <Link>Properties\Version.cs</Link>
     </Compile>
+    <Compile Include="Commands\Checkout.cs" />
     <Compile Include="Commands\ResetRemote.cs" />
     <Compile Include="Commands\Create.cs" />
     <Compile Include="Commands\ListRemoteBranches.cs" />