feature: merge multiple heads (#793)

* feature: allow merging multiple heads
* feature: allow merging multiple branches from branch tree

src/ViewModels/MergeMultiple.cs

@@ -0,0 +1,59 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using SourceGit.Models;
+
+namespace SourceGit.ViewModels
+{
+    public class MergeMultiple : Popup
+    {
+        public List<string> Strategies = ["octopus", "ours"];
+
+        public List<Commit> Targets
+        {
+            get;
+            private set;
+        }
+
+        public bool AutoCommit
+        {
+            get;
+            set;
+        }
+
+        public MergeStrategy Strategy
+        {
+            get;
+            set;
+        }
+
+        public MergeMultiple(Repository repo, List<Commit> targets)
+        {
+            _repo = repo;
+            Targets = targets;
+            AutoCommit = true;
+            Strategy = MergeStrategy.ForMultiple.Find(s => s.Arg == null);
+            View = new Views.MergeMultiple() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = "Merge head(s) ...";
+
+            return Task.Run(() =>
+            {
+                var succ = new Commands.Merge(
+                    _repo.FullPath,
+                    string.Join(" ", Targets.ConvertAll(c => c.Decorators.Find(d => d.Type == DecoratorType.RemoteBranchHead || d.Type == DecoratorType.LocalBranchHead)?.Name ?? c.Decorators.Find(d => d.Type == DecoratorType.Tag)?.Name ?? c.SHA)),
+                    AutoCommit ? string.Empty : "--no-commit",
+                    Strategy?.Arg,
+                    SetProgressDescription).Exec();
+
+                CallUIThread(() => _repo.SetWatcherEnabled(true));
+                return succ;
+            });
+        }
+
+        private readonly Repository _repo = null;
+    }
+}