FModel/FModel/Helper.cs

using System;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows;

namespace FModel
{
    public static class Helper
    {
        [StructLayout(LayoutKind.Explicit)]
        private struct NanUnion
        {
            [FieldOffset(0)]
            internal double DoubleValue;
            [FieldOffset(0)]
            internal readonly ulong UlongValue;
        }

        public static void OpenWindow<T>(string windowName, Action action) where T : Window
        {
            if (!IsWindowOpen<T>(windowName))
            {
                action();
            }
            else
            {
                var w = GetOpenedWindow<T>(windowName);
                if (windowName == "Search View") w.WindowState = WindowState.Normal;
                w.Focus();
            }
        }

        public static T GetWindow<T>(string windowName, Action action) where T : Window
        {
            if (!IsWindowOpen<T>(windowName))
            {
                action();
            }

            var ret = (T) GetOpenedWindow<T>(windowName);
            ret.Focus();
            ret.Activate();
            return ret;
        }

        public static void CloseWindow<T>(string windowName) where T : Window
        {
            if (!IsWindowOpen<T>(windowName)) return;
            GetOpenedWindow<T>(windowName).Close();
        }

        private static bool IsWindowOpen<T>(string name = "") where T : Window
        {
            return string.IsNullOrEmpty(name)
                ? Application.Current.Windows.OfType<T>().Any()
                : Application.Current.Windows.OfType<T>().Any(w => w.Title.Equals(name));
        }

        private static Window GetOpenedWindow<T>(string name) where T : Window
        {
            return Application.Current.Windows.OfType<T>().FirstOrDefault(w => w.Title.Equals(name));
        }

        public static bool IsNaN(double value)
        {
            var t = new NanUnion {DoubleValue = value};
            var exp = t.UlongValue & 0xfff0000000000000;
            var man = t.UlongValue & 0x000fffffffffffff;
            return exp is 0x7ff0000000000000 or 0xfff0000000000000 && man != 0;
        }

        public static bool AreVirtuallyEqual(double d1, double d2)
        {
            if (double.IsPositiveInfinity(d1))
                return double.IsPositiveInfinity(d2);

            if (double.IsNegativeInfinity(d1))
                return double.IsNegativeInfinity(d2);

            if (IsNaN(d1))
                return IsNaN(d2);

            var n = d1 - d2;
            var d = (Math.Abs(d1) + Math.Abs(d2) + 10) * 1.0e-15;
            return -d < n && d > n;
        }
    }
}