using System;
using System.Linq;
using Sandbox.Diagnostics;

namespace BetterUI;

/// <summary>
/// A panel that will only render if a condition is true. The condition is a
/// function that is called every frame to check if the panel should be
/// rendered.
/// </summary>
public partial class ConditionalRender : Panel
{
	private bool _previousCondition;

	/// <summary>
	/// The condition function that determines if the panel should be rendered.
	/// </summary>
	public Func<bool> Condition { get; set; } = null!;

	protected override void OnAfterTreeRender( bool firstTime )
	{
		Assert.NotNull( Condition, "ConditionalRender must have a condition function" );
	}

	public override void Tick()
	{
		var condition = Condition();

		if ( _previousCondition == condition ) return;
		_previousCondition = condition;

		for ( var i = 0; i < Children.Count(); i++ )
		{
			var child = Children.ElementAt(i);
			if ( !child.IsValid() ) continue;
			
			child.BindClass("hidden", () => !condition);
		}
	}

	protected override int BuildHash() => HashCode.Combine( Condition.Invoke() );
}