DiscordChatExporter/DiscordChatExporter.Gui/Converters/TimeSpanToDateTimeConverter.cs

using System;
using System.Globalization;
using System.Windows.Data;

namespace DiscordChatExporter.Gui.Converters;

[ValueConversion(typeof(TimeSpan?), typeof(DateTime?))]
public class TimeSpanToDateTimeConverter : IValueConverter
{
    public static TimeSpanToDateTimeConverter Instance { get; } = new();

    public object? Convert(object value, Type targetType, object parameter, CultureInfo culture) => 
        value is TimeSpan timeSpanValue
            ? DateTime.Today.Add(timeSpanValue)
            : default(DateTime?);

    public object? ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) => 
        value is DateTime dateTimeValue
            ? dateTimeValue.TimeOfDay 
            : default(TimeSpan?);
}