feature: git command logs

Signed-off-by: leo <longshuang@msn.cn>

src/ViewModels/CommandLog.cs

@@ -0,0 +1,87 @@
+using System;
+using System.Text;
+using Avalonia.Threading;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace SourceGit.ViewModels
+{
+    public class CommandLog : ObservableObject, Models.ICommandLog
+    {
+        public string Name
+        {
+            get;
+            private set;
+        } = string.Empty;
+
+        public DateTime Time
+        {
+            get;
+        } = DateTime.Now;
+
+        public string TimeStr
+        {
+            get => Time.ToString("T");
+        }
+
+        public bool IsComplete
+        {
+            get;
+            private set;
+        } = false;
+
+        public string Content
+        {
+            get
+            {
+                return IsComplete ? _content : _builder.ToString();
+            }
+        }
+
+        public CommandLog(string name)
+        {
+            Name = name;
+        }
+
+        public void Register(Action<string> handler)
+        {
+            if (!IsComplete)
+                _onNewLineReceived += handler;
+        }
+
+        public void AppendLine(string line = null)
+        {
+            var newline = line ?? string.Empty;
+
+            Dispatcher.UIThread.Invoke(() =>
+            {
+                _builder.AppendLine(newline);
+                _onNewLineReceived?.Invoke(newline);
+            });
+        }
+
+        public void Complete()
+        {
+            IsComplete = true;
+
+            Dispatcher.UIThread.Invoke(() =>
+            {
+                _content = _builder.ToString();
+                _builder.Clear();
+                _builder = null;
+
+                OnPropertyChanged(nameof(IsComplete));
+
+                if (_onNewLineReceived != null)
+                {
+                    var dumpHandlers = _onNewLineReceived.GetInvocationList();
+                    foreach (var d in dumpHandlers)
+                        _onNewLineReceived -= (Action<string>)d;
+                }
+            });
+        }
+
+        private string _content = string.Empty;
+        private StringBuilder _builder = new StringBuilder();
+        private event Action<string> _onNewLineReceived; 
+    }
+}