// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using osu.Framework.Allocation;
using osu.Framework.Bindables;
using osu.Framework.Extensions.Color4Extensions;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Colour;
using osu.Framework.Graphics.Containers;
using osu.Framework.Graphics.Shapes;
using osu.Game.Rulesets.UI.Scrolling;
using osuTK.Graphics;

namespace osu.Game.Rulesets.Mania.UI
{
    /// <summary>
    /// A <see cref="Container"/> that has its contents partially hidden by an adjustable "cover". This is intended to be used in a playfield.
    /// </summary>
    /// <remarks>
    /// The covered area extends in the scrolling direction, with its size depending on <see cref="Coverage"/>.
    /// </remarks>
    public class PlayfieldCoveringContainer : CompositeDrawable
    {
        /// <summary>
        /// The complete cover, including gradient and fill.
        /// </summary>
        protected readonly Drawable Cover;

        /// <summary>
        /// The gradient portion of the cover.
        /// </summary>
        private readonly Box gradient;

        /// <summary>
        /// The fully-opaque portion of the cover.
        /// </summary>
        private readonly Box filled;

        private readonly IBindable<ScrollingDirection> scrollDirection = new Bindable<ScrollingDirection>();

        public PlayfieldCoveringContainer(Drawable content)
        {
            InternalChild = new BufferedContainer
            {
                RelativeSizeAxes = Axes.Both,
                Children = new[]
                {
                    content,
                    Cover = new Container
                    {
                        Anchor = Anchor.Centre,
                        Origin = Anchor.Centre,
                        RelativeSizeAxes = Axes.Both,
                        Blending = new BlendingParameters
                        {
                            // Don't change the destination colour.
                            RGBEquation = BlendingEquation.Add,
                            Source = BlendingType.Zero,
                            Destination = BlendingType.One,
                            // Subtract the cover's alpha from the destination (points with alpha 1 should make the destination completely transparent).
                            AlphaEquation = BlendingEquation.Add,
                            SourceAlpha = BlendingType.Zero,
                            DestinationAlpha = BlendingType.OneMinusSrcAlpha
                        },
                        Children = new Drawable[]
                        {
                            gradient = new Box
                            {
                                Anchor = Anchor.BottomLeft,
                                Origin = Anchor.BottomLeft,
                                RelativeSizeAxes = Axes.Both,
                                RelativePositionAxes = Axes.Both,
                                Height = 0.25f,
                                Colour = ColourInfo.GradientVertical(
                                    Color4.White.Opacity(0f),
                                    Color4.White.Opacity(1f)
                                )
                            },
                            filled = new Box
                            {
                                Anchor = Anchor.BottomLeft,
                                Origin = Anchor.BottomLeft,
                                RelativeSizeAxes = Axes.Both,
                                Height = 0
                            }
                        }
                    }
                }
            };
        }

        [BackgroundDependencyLoader]
        private void load(IScrollingInfo scrollingInfo)
        {
            scrollDirection.BindTo(scrollingInfo.Direction);
            scrollDirection.BindValueChanged(onScrollDirectionChanged, true);
        }

        private void onScrollDirectionChanged(ValueChangedEvent<ScrollingDirection> direction)
            => Cover.Rotation = direction.NewValue == ScrollingDirection.Up ? 0 : 180f;

        /// <summary>
        /// The relative area that should be completely covered. This does not include the fade.
        /// </summary>
        public float Coverage
        {
            set
            {
                filled.Height = value;
                gradient.Y = -value;
            }
        }
    }
}