enhance: slightly improve statistics (#711)

* use preference MaxHistoryCommits
* use current culture to adjust first days of the week

Author: czarkoff

src/Commands/Statistics.cs

@@ -1,4 +1,5 @@
 using System;
+using SourceGit.ViewModels;
 
 namespace SourceGit.Commands
 {
@@ -8,7 +9,7 @@ public Statistics(string repo)
         {
             WorkingDirectory = repo;
             Context = repo;
-            Args = $"log --date-order --branches --remotes -40000 --pretty=format:\"%ct$%aN\"";
+            Args = $"log --date-order --branches --remotes -{Preference.Instance.MaxHistoryCommits} --pretty=format:\"%ct$%aN\"";
         }
 
         public Models.Statistics Result()

src/Models/Statistics.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-
+using System.Globalization;
 using LiveChartsCore;
 using LiveChartsCore.Defaults;
 using LiveChartsCore.SkiaSharpView;
@@ -138,7 +138,7 @@ public class Statistics
         public Statistics()
         {
             _today = DateTime.Now.ToLocalTime().Date;
-            _thisWeekStart = _today.AddSeconds(-(int)_today.DayOfWeek * 3600 * 24);
+            _thisWeekStart = _today.AddDays(((int)_today.DayOfWeek + (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek) % 7 - 7);
             _thisMonthStart = _today.AddDays(1 - _today.Day);
 
             All = new StatisticsReport(StaticsticsMode.All, DateTime.MinValue);