using Microsoft.Xaml.Behaviors;

using System.Windows;
using System.Windows.Controls;

namespace Sai.Toolkit.Mvvm.Behaviors;

/// <summary>
///     在xaml的资源中声明，viewModel继承IValidationExceptionHandler，通过IsValid判断能否执行
/// </summary>
public class ValidationRuleBehavior : Behavior<FrameworkElement>
{
	private int errorCount;

	protected override void OnAttached()
	{
		base.OnAttached();
		AssociatedObject.AddHandler(Validation.ErrorEvent, new EventHandler<ValidationErrorEventArgs>(OnValidationError));
	}

	protected override void OnDetaching()
	{
		AssociatedObject.RemoveHandler(Validation.ErrorEvent, new EventHandler<ValidationErrorEventArgs>(OnValidationError));
	}

	private void OnValidationError(object sender, ValidationErrorEventArgs e)
	{
		if (AssociatedObject.DataContext is IValidationExceptionHandler handler)
		{
			if (e.OriginalSource is UIElement elem)
			{
				if (e.Action == ValidationErrorEventAction.Added)
				{
					errorCount++;
				}
				else if (e.Action == ValidationErrorEventAction.Removed)
				{
					errorCount--;
				}
			}

			handler.IsValid = errorCount == 0;
		}
	}
}