using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Graphics.PackedVector;
using nulltech.Cameras;
using nulltech.Services;

namespace nulltech.Illumination.AO
{
    public abstract class AmbientOcclusion
    {
        private const int RandomTextureSize = 64;
        protected readonly VertexPositionTexture[] Vertices = new VertexPositionTexture[4];
        private readonly Vector3[] _cornersViewSpace = new Vector3[8];
        private readonly Vector3[] _cornersWorldSpace = new Vector3[8];
        private readonly Vector3[] _currentFrustumCorners = new Vector3[4];
        private readonly BoundingFrustum _frustum = new BoundingFrustum(Matrix.Identity);
        protected Effect AOEffect;
        private EffectParameter _cornerParam;
        private EffectParameter _farParam;
        private EffectParameter _inverseViewportParam;
        private EffectParameter _randomTextureParam;
        private EffectParameter _rayParam;
        private Texture2D _randomTexture;

        protected AmbientOcclusion(EngineServices services)
        {
            GraphicsDevice = services.GraphicsDevice;
            Content = services.ContentManager;

            GenerateQuad();

            GenerateRandomTexture();
        }

        public ContentManager Content { get; private set; }

        public GraphicsDevice GraphicsDevice { get; private set; }

        public abstract void Calculate(CameraEntity camera);

        public abstract void Draw(CameraEntity camera);

        private void GenerateRandomTexture()
        {
            _randomTexture = new Texture2D(GraphicsDevice, RandomTextureSize, RandomTextureSize, false,
                                           SurfaceFormat.HalfVector2);

            var rand = new Random();

            var samples = new HalfVector2[RandomTextureSize * RandomTextureSize];

            for (int i = 0; i < RandomTextureSize * RandomTextureSize; i++)
            {
                Vector2 sVec = Vector2.Zero;
                sVec.X = (float)((rand.NextDouble() - .5) * 2.0);
                sVec.Y = (float)((rand.NextDouble() - .5) * 2.0);
                sVec.Normalize();
                samples[i] = new HalfVector2(sVec);
            }

            _randomTexture.SetData(samples);
        }

        protected void GenerateQuad()
        {
            Vertices[0].Position = new Vector3(-1, 1, 1);
            Vertices[1].Position = new Vector3(1, 1, 1);
            Vertices[2].Position = new Vector3(-1, -1, 1);
            Vertices[3].Position = new Vector3(1, -1, 1);

            Vertices[0].TextureCoordinate = new Vector2(0, 0);
            Vertices[1].TextureCoordinate = new Vector2(1, 0);
            Vertices[2].TextureCoordinate = new Vector2(0, 1);
            Vertices[3].TextureCoordinate = new Vector2(1, 1);
        }

        protected void GenerateCorners(CameraEntity camera)
        {
            _inverseViewportParam.SetValue(camera.InverseViewport);

            _farParam.SetValue(camera.ProjectionController.Far);

            _frustum.Matrix = camera.ViewProjection;
            _frustum.GetCorners(_cornersWorldSpace);

            Matrix matView = camera.View;

            Vector3.Transform(_cornersWorldSpace, ref matView, _cornersViewSpace);

            for (int i = 0; i < 4; i++) //take only the 4 farthest points
            {
                _currentFrustumCorners[i] = _cornersViewSpace[i + 4];
            }

            Vector3 temp = _currentFrustumCorners[3];
            _currentFrustumCorners[3] = _currentFrustumCorners[2];
            _currentFrustumCorners[2] = temp;

            _cornerParam.SetValue(_currentFrustumCorners);

            _rayParam.SetValue(_currentFrustumCorners[1]);
        }

        protected virtual void ProcessEffect()
        {
            _inverseViewportParam = AOEffect.Parameters["InverseViewportDimensions"];
            _cornerParam = AOEffect.Parameters["FrustumCorners"];
            _rayParam = AOEffect.Parameters["FrustumRay"];
            _farParam = AOEffect.Parameters["Far"];
            _randomTextureParam = AOEffect.Parameters["RandomTexture"];

            _randomTextureParam.SetValue(_randomTexture);
        }
    }
}