project: reorganize the structure of the project.

* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.

src/Commands/Fetch.cs

@@ -0,0 +1,158 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SourceGit.Commands
+{
+    public class Fetch : Command
+    {
+        public Fetch(string repo, string remote, bool prune, Action<string> outputHandler)
+        {
+            _outputHandler = outputHandler;
+            WorkingDirectory = repo;
+            Context = repo;
+            TraitErrorAsOutput = true;
+
+            var sshKey = new Config(repo).Get($"remote.{remote}.sshkey");
+            if (!string.IsNullOrEmpty(sshKey))
+            {
+                Args = $"-c core.sshCommand=\"ssh -i '{sshKey}'\" ";
+            }
+            else
+            {
+                Args = "-c credential.helper=manager ";
+            }
+
+            Args += "fetch --progress --verbose ";
+            if (prune)
+                Args += "--prune ";
+            Args += remote;
+
+            AutoFetch.MarkFetched(repo);
+        }
+
+        public Fetch(string repo, string remote, string localBranch, string remoteBranch, Action<string> outputHandler)
+        {
+            _outputHandler = outputHandler;
+            WorkingDirectory = repo;
+            Context = repo;
+            TraitErrorAsOutput = true;
+
+            var sshKey = new Config(repo).Get($"remote.{remote}.sshkey");
+            if (!string.IsNullOrEmpty(sshKey))
+            {
+                Args = $"-c core.sshCommand=\"ssh -i '{sshKey}'\" ";
+            }
+            else
+            {
+                Args = "-c credential.helper=manager ";
+            }
+
+            Args += $"fetch --progress --verbose {remote} {remoteBranch}:{localBranch}";
+        }
+
+        protected override void OnReadline(string line)
+        {
+            _outputHandler?.Invoke(line);
+        }
+
+        private readonly Action<string> _outputHandler;
+    }
+
+    public class AutoFetch
+    {
+        private const double INTERVAL = 10 * 60;
+
+        public static bool IsEnabled
+        {
+            get;
+            set;
+        } = false;
+
+        class Job
+        {
+            public Fetch Cmd = null;
+            public DateTime NextRunTimepoint = DateTime.MinValue;
+        }
+
+        static AutoFetch()
+        {
+            Task.Run(() =>
+            {
+                while (true)
+                {
+                    if (!IsEnabled)
+                    {
+                        Thread.Sleep(10000);
+                        continue;
+                    }
+
+                    var now = DateTime.Now;
+                    var uptodate = new List<Job>();
+                    lock (_lock)
+                    {
+                        foreach (var job in _jobs)
+                        {
+                            if (job.Value.NextRunTimepoint.Subtract(now).TotalSeconds <= 0)
+                            {
+                                uptodate.Add(job.Value);
+                            }
+                        }
+                    }
+
+                    foreach (var job in uptodate)
+                    {
+                        job.Cmd.Exec();
+                        job.NextRunTimepoint = DateTime.Now.AddSeconds(INTERVAL);
+                    }
+
+                    Thread.Sleep(2000);
+                }
+            });
+        }
+
+        public static void AddRepository(string repo)
+        {
+            var job = new Job
+            {
+                Cmd = new Fetch(repo, "--all", true, null) { RaiseError = false },
+                NextRunTimepoint = DateTime.Now.AddSeconds(INTERVAL),
+            };
+
+            lock (_lock)
+            {
+                if (_jobs.ContainsKey(repo))
+                {
+                    _jobs[repo] = job;
+                }
+                else
+                {
+                    _jobs.Add(repo, job);
+                }
+            }
+        }
+
+        public static void RemoveRepository(string repo)
+        {
+            lock (_lock)
+            {
+                _jobs.Remove(repo);
+            }
+        }
+
+        public static void MarkFetched(string repo)
+        {
+            lock (_lock)
+            {
+                if (_jobs.TryGetValue(repo, out var value))
+                {
+                    value.NextRunTimepoint = DateTime.Now.AddSeconds(INTERVAL);
+                }
+            }
+        }
+
+        private static readonly Dictionary<string, Job> _jobs = new Dictionary<string, Job>();
+        private static readonly object _lock = new object();
+    }
+}