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

namespace Melskin.Converters;

/// <summary>
/// 支持判断是否为 null 或空字符串，以及是否为非 null 且非空字符串的转换器
/// </summary>
public class NullOrEmptyConverter : IValueConverter
{
    private readonly bool isNotNullOrEmpty;

    /// <summary>
    /// 判断对象是否为 null 或空字符串的单例实例
    /// </summary>
    public static readonly NullOrEmptyConverter Instance = new(false);

    /// <summary>
    /// 判断对象是否为非 null 且非空字符串的单例实例
    /// </summary>
    public static readonly NullOrEmptyConverter NotInstance = new(true);

    private NullOrEmptyConverter(bool isNotNullOrEmpty = false)
    {
        this.isNotNullOrEmpty = isNotNullOrEmpty;
    }

    /// <inheritdoc/>
    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        // 如果值为 null 或空字符串，则返回 true；否则返回 false
        var result = value == null || string.IsNullOrEmpty(value.ToString());
        return isNotNullOrEmpty ? !result : result;
    }

    /// <inheritdoc/>
    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        return DependencyProperty.UnsetValue;
    }
}