namespace Sandbox.UI
{
	/// <summary>
	/// A generic box that displays a given texture within itself.
	/// </summary>
	[Library( "image" ), Alias( "img" ), Expose]
	public partial class Image : Panel
	{
		/// <summary>
		/// The texture being displayed by this panel.
		/// </summary>
		public Texture Texture { get; set; }

		public override bool HasContent => Texture != null;

		public Image()
		{
			YogaNode.SetMeasureFunction( MeasureTexture );
		}

		/// <summary>
		/// Set <see cref="Texture"/> from a file path. URLs supported.
		/// </summary>
		public async void SetTexture( string name )
		{
			if ( string.IsNullOrWhiteSpace( name ) ) return;
			if ( !IsValid ) return;

			Texture = await Texture.LoadAsync( name );

			if ( !IsValid ) return;
			YogaNode.MarkDirty(); // Update MeasureTexture
		}

		float oldScaleToScreen = 1.0f;
		internal override void PreLayout( LayoutCascade cascade )
		{
			base.PreLayout( cascade );

			if ( ScaleToScreen != oldScaleToScreen )
			{
				YogaNode.MarkDirty();
			}
		}

		internal override void DrawContent( PanelRenderer renderer, ref RenderState state )
		{
			if ( Texture == null )
				return;

			if ( renderer is PanelRenderer pr )
			{
				var length = ComputedStyle.ObjectFit switch
				{
					ObjectFit.Contain => Length.Contain,
					ObjectFit.Cover => Length.Cover,
					ObjectFit.Fill => Length.Percent( 100 ).Value,
					_ => Length.Auto,
				};

				pr.DrawBackgroundTexture( this, Texture, state, length );
			}
		}

		public override void SetProperty( string name, string value )
		{
			base.SetProperty( name, value );

			if ( name == "src" ) SetTexture( value );
		}

		internal Vector2 MeasureTexture( YGNodeRef node, float width, YGMeasureMode widthMode, float height, YGMeasureMode heightMode )
		{
			if ( !Texture.IsValid() ) return default;

			try
			{
				var (w, h) = (Texture.Width, Texture.Height);
				var exact = YGMeasureMode.YGMeasureModeExactly;
				var atMost = YGMeasureMode.YGMeasureModeAtMost;

				oldScaleToScreen = ScaleToScreen;
				var ideal = new Vector2( w * ScaleToScreen, h * ScaleToScreen );

				if ( widthMode == exact ) return new Vector2( width, h * width / w );
				if ( heightMode == exact ) return new Vector2( w * height / h, height );

				if ( widthMode == atMost && heightMode == atMost && (width < ideal.x || height < ideal.y) )
				{
					float scale = Math.Min( width / w, height / h );
					return new Vector2( w * scale, h * scale );
				}

				if ( widthMode == atMost && width < ideal.x ) return new Vector2( width, h * width / w );
				if ( heightMode == atMost && height < ideal.y ) return new Vector2( w * height / h, height );

				return ideal;
			}
			catch ( System.Exception e )
			{
				Log.Warning( e );
				return default;
			}
		}

	}

	namespace Construct
	{
		public static class ImageConstructor
		{
			/// <summary>
			/// Create an image with given texture and CSS classname.
			/// </summary>
			public static Image Image( this PanelCreator self, string image = null, string classname = null )
			{
				var control = self.panel.AddChild<Image>();

				if ( image != null )
					control.SetTexture( image );

				if ( classname != null )
					control.AddClass( classname );

				return control;
			}
		}
	}
}