//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE

using System.Linq;
using osu.Framework.Allocation;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Batches;
using osu.Framework.Graphics.Containers;
using osu.Framework.Graphics.Shaders;
using osu.Framework.Graphics.Sprites;
using osu.Framework.Graphics.Textures;
using osu.Framework.Input;
using osu.Framework.MathUtils;
using OpenTK;
using System;
using osu.Framework.Graphics.OpenGL;
using osu.Framework.Graphics.OpenGL.Buffers;
using System.Collections.Concurrent;
using OpenTK.Graphics.ES30;
using System.Collections.Generic;
using System.Diagnostics;

namespace osu.Game.Graphics.Cursor
{
    class TrailSprite : Sprite
    {
        private Shader shader;

        public TrailSprite()
        {
            Origin = Anchor.Centre;
        }

        protected override DrawNode CreateDrawNode() => new TrailSpriteDrawNode();

        protected override void ApplyDrawNode(DrawNode node)
        {
            base.ApplyDrawNode(node);

            TrailSpriteDrawNode sNode = node as TrailSpriteDrawNode;
            sNode.RoundedTextureShader = sNode.TextureShader = shader;
            sNode.NeedsUpdate = true;
        }

        public override bool IsVisible => true;

        [BackgroundDependencyLoader]
        private void load(ShaderManager shaders, TextureStore textures)
        {
            shader = shaders?.Load(@"CursorTrail", FragmentShaderDescriptor.Texture);
            Texture = textures.Get(@"Cursor/cursortrail");
        }
    }

    class TrailSpriteDrawNode : SpriteDrawNode
    {
        public bool NeedsUpdate;
    }

    class CursorTrail : Container<TrailSprite>
    {
        public override bool Contains(Vector2 screenSpacePos) => true;

        int currentIndex;

        protected override bool CanBeFlattened => false;

        Shader shader;

        private double timeOffset;

        private float time;
        
        TrailDrawNodeSharedData trailDrawNodeSharedData = new TrailDrawNodeSharedData();
        const int MAX_SPRITES = 2048;

        Vector2? lastPosition;

        protected override DrawNode CreateDrawNode() => new TrailDrawNode();

        protected override void ApplyDrawNode(DrawNode node)
        {
            base.ApplyDrawNode(node);

            TrailDrawNode tNode = node as TrailDrawNode;
            tNode.Shader = shader;
            tNode.Time = time;
            tNode.Shared = trailDrawNodeSharedData;
        }

        public CursorTrail()
        {
            RelativeSizeAxes = Axes.Both;

            for (int i = 0; i < MAX_SPRITES; i++)
                AddInternal(new TrailSprite());
        }

        [BackgroundDependencyLoader]
        private void load(ShaderManager shaders)
        {
            shader = shaders?.Load(@"CursorTrail", FragmentShaderDescriptor.Texture);
        }

        protected override void Update()
        {
            base.Update();

            Invalidate(Invalidation.DrawNode, shallPropagate: false);

            int fadeClockResetThreshold = 1000000;

            time = (float)(Time.Current - timeOffset) / 500f;
            if (time > fadeClockResetThreshold)
                ResetTime();
        }

        private void ResetTime()
        {
            foreach (var c in Children)
                c.Alpha -= time;

            time = 0;
            timeOffset = Time.Current;
        }

        protected override bool OnMouseMove(InputState state)
        {
            if (lastPosition == null)
            {
                lastPosition = state.Mouse.Position;
                return base.OnMouseMove(state);
            }

            Vector2 pos1 = lastPosition.Value;
            Vector2 pos2 = state.Mouse.Position;

            Vector2 diff = pos2 - pos1;
            float distance = diff.Length;
            Vector2 direction = diff / distance;

            float interval = this[0].DrawSize.X / 2;

            for (float d = interval; d < distance; d += interval)
            {
                lastPosition = pos1 + direction * d;
                addPosition(lastPosition.Value);
            }

            return base.OnMouseMove(state);
        }

        private void addPosition(Vector2 pos)
        {
            var s = this[currentIndex];
            s.Position = pos;
            s.Alpha = time + 1f;

            currentIndex = (currentIndex + 1) % MAX_SPRITES;
        }

        public class TrailDrawNodeSharedData
        {
            public VertexBuffer<TexturedVertex2D> VertexBuffer;
        }

        class TrailDrawNode : ContainerDrawNode
        {
            public new Shader Shader;
            public float Time;
            public TrailDrawNodeSharedData Shared;

            public override void Draw(Action<TexturedVertex2D> vertexAction)
            {
                if (Shared.VertexBuffer == null)
                    Shared.VertexBuffer = new QuadVertexBuffer<TexturedVertex2D>(MAX_SPRITES, BufferUsageHint.DynamicDraw);

                Shader.GetUniform<float>("g_FadeClock").Value = Time;

                int updateStart = -1, updateEnd = 0;
                int test = 0;
                for (int i = 0; i < Children.Count; ++i)
                {
                    TrailSpriteDrawNode tNode = Children[i] as TrailSpriteDrawNode;
                    if (tNode.NeedsUpdate)
                    {
                        if (updateStart == -1)
                            updateStart = i;
                        updateEnd = i + 1;

                        int start = i * 4;
                        int end = start;
                        tNode.Draw(delegate (TexturedVertex2D v)
                        {
                            Shared.VertexBuffer.Vertices[end++] = v;
                        });

                        tNode.NeedsUpdate = false;
                    }
                    else if (updateStart != -1)
                    {
                        Shared.VertexBuffer.UpdateRange(updateStart * 4, updateEnd * 4);
                        updateStart = -1;
                    }
                }

                // Update all remaining vertices that have been changed.
                if (updateStart != -1)
                    Shared.VertexBuffer.UpdateRange(updateStart * 4, updateEnd * 4);

                SpriteDrawNode sNode = Children[0] as SpriteDrawNode;
                sNode.Texture.TextureGL.Bind();
                sNode.TextureShader.Bind();

                Shared.VertexBuffer.Draw();

                sNode.TextureShader.Unbind();
            }
        }
    }
}