feature: add context menu for both branch and commit to compare selected with current HEAD

src/Commands/QuerySingleCommit.cs

@@ -0,0 +1,167 @@
+using System;
+using System.Collections.Generic;
+
+namespace SourceGit.Commands
+{
+    public class QuerySingleCommit : Command
+    {
+        private const string GPGSIG_START = "gpgsig -----BEGIN PGP SIGNATURE-----";
+        private const string GPGSIG_END = " -----END PGP SIGNATURE-----";
+
+        public QuerySingleCommit(string repo, string sha) {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"show --pretty=raw --decorate=full -s {sha}";
+        }
+
+        public Models.Commit Result()
+        {
+            var succ = Exec();
+            if (!succ)
+                return null;
+
+            _commit.Message.Trim();
+            return _commit;
+        }
+
+        protected override void OnReadline(string line)
+        {
+            if (isSkipingGpgsig)
+            {
+                if (line.StartsWith(GPGSIG_END, StringComparison.Ordinal))
+                    isSkipingGpgsig = false;
+                return;
+            }
+            else if (line.StartsWith(GPGSIG_START, StringComparison.Ordinal))
+            {
+                isSkipingGpgsig = true;
+                return;
+            }
+
+            if (line.StartsWith("commit ", StringComparison.Ordinal))
+            {
+                line = line.Substring(7);
+
+                var decoratorStart = line.IndexOf('(', StringComparison.Ordinal);
+                if (decoratorStart < 0)
+                {
+                    _commit.SHA = line.Trim();
+                }
+                else
+                {
+                    _commit.SHA = line.Substring(0, decoratorStart).Trim();
+                    ParseDecorators(_commit.Decorators, line.Substring(decoratorStart + 1));
+                }
+
+                return;
+            }
+
+            if (line.StartsWith("tree ", StringComparison.Ordinal))
+            {
+                return;
+            }
+            else if (line.StartsWith("parent ", StringComparison.Ordinal))
+            {
+                _commit.Parents.Add(line.Substring("parent ".Length));
+            }
+            else if (line.StartsWith("author ", StringComparison.Ordinal))
+            {
+                Models.User user = Models.User.Invalid;
+                ulong time = 0;
+                Models.Commit.ParseUserAndTime(line.Substring(7), ref user, ref time);
+                _commit.Author = user;
+                _commit.AuthorTime = time;
+            }
+            else if (line.StartsWith("committer ", StringComparison.Ordinal))
+            {
+                Models.User user = Models.User.Invalid;
+                ulong time = 0;
+                Models.Commit.ParseUserAndTime(line.Substring(10), ref user, ref time);
+                _commit.Committer = user;
+                _commit.CommitterTime = time;
+            }
+            else if (string.IsNullOrEmpty(_commit.Subject))
+            {
+                _commit.Subject = line.Trim();
+            }
+            else
+            {
+                _commit.Message += (line.Trim() + "\n");
+            }
+        }
+
+        private bool ParseDecorators(List<Models.Decorator> decorators, string data)
+        {
+            bool isHeadOfCurrent = false;
+
+            var subs = data.Split(new char[] { ',', ')', '(' }, StringSplitOptions.RemoveEmptyEntries);
+            foreach (var sub in subs)
+            {
+                var d = sub.Trim();
+                if (d.StartsWith("tag: refs/tags/", StringComparison.Ordinal))
+                {
+                    decorators.Add(new Models.Decorator()
+                    {
+                        Type = Models.DecoratorType.Tag,
+                        Name = d.Substring(15).Trim(),
+                    });
+                }
+                else if (d.EndsWith("/HEAD", StringComparison.Ordinal))
+                {
+                    continue;
+                }
+                else if (d.StartsWith("HEAD -> refs/heads/", StringComparison.Ordinal))
+                {
+                    isHeadOfCurrent = true;
+                    decorators.Add(new Models.Decorator()
+                    {
+                        Type = Models.DecoratorType.CurrentBranchHead,
+                        Name = d.Substring(19).Trim(),
+                    });
+                }
+                else if (d.Equals("HEAD"))
+                {
+                    isHeadOfCurrent = true;
+                    decorators.Add(new Models.Decorator()
+                    {
+                        Type = Models.DecoratorType.CurrentCommitHead,
+                        Name = d.Trim(),
+                    });
+                }
+                else if (d.StartsWith("refs/heads/", StringComparison.Ordinal))
+                {
+                    decorators.Add(new Models.Decorator()
+                    {
+                        Type = Models.DecoratorType.LocalBranchHead,
+                        Name = d.Substring(11).Trim(),
+                    });
+                }
+                else if (d.StartsWith("refs/remotes/", StringComparison.Ordinal))
+                {
+                    decorators.Add(new Models.Decorator()
+                    {
+                        Type = Models.DecoratorType.RemoteBranchHead,
+                        Name = d.Substring(13).Trim(),
+                    });
+                }
+            }
+
+            decorators.Sort((l, r) =>
+            {
+                if (l.Type != r.Type)
+                {
+                    return (int)l.Type - (int)r.Type;
+                }
+                else
+                {
+                    return l.Name.CompareTo(r.Name);
+                }
+            });
+
+            return isHeadOfCurrent;
+        }
+
+        private Models.Commit _commit = new Models.Commit();
+        private bool isSkipingGpgsig = false;
+    }
+}