using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Data;

namespace WpfAppTest
{
    internal class UnitConverter : IValueConverter
    {
        private string DefaultUnit { get; set; } = "mm";

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value == null)
                return null;

            if (value is double d)
            {
                string unit = parameter as string ?? DefaultUnit;
                // 使用StringFormat时，value会先被格式化，这里直接拼接单位
                return $"{d.ToString(culture)} {unit}";
            }

            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is string str)
            {
                // 提取纯数字字符串（允许中间态如 '1.', '-.'）
                str = str.Trim();

                var match = Regex.Match(str, @"[-+]?[0-9]*\.?[0-9]*");
                if (match.Success)
                {
                    string numberPart = match.Value;

                    // 处理中间态输入，允许返回未完成的文本（让 UI 不抖动）
                    if (string.IsNullOrEmpty(numberPart) || numberPart.EndsWith("-") || numberPart.EndsWith(".") || numberPart.EndsWith("-."))
                        return DependencyProperty.UnsetValue;

                    if (double.TryParse(numberPart, NumberStyles.Any, culture, out double result))
                        return result;
                }
            }

            return DependencyProperty.UnsetValue;
        }
    }
}