MainWindow.xaml.cs

using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WindowResizer
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void TitleBar_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            if (e.ClickCount == 2)
            {
                ToggleMaximize();
                return;
            }

            DragMove();
        }

        private void ToggleMaximize()
        {
            if (WindowState == WindowState.Maximized)
                WindowState = WindowState.Normal;
            else
                WindowState = WindowState.Maximized;
        }

        private void Min_Click(object sender, RoutedEventArgs e) => WindowState = WindowState.Minimized;
        private void Max_Click(object sender, RoutedEventArgs e) => ToggleMaximize();
        private void Close_Click(object sender, RoutedEventArgs e) => Close();
    }
}