using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Aiwaz.Contracts;
using SlimDX;

namespace Aiwaz.Resources
{
    public class PickHull : IPickHull
    {
        private VertexElement positionElement;
        private int strideToPosition;

        private DataStream vertexData;
        private int vertexCount;
        private VertexElement[] vertexElements;
        private int vertexElementSize;

        private DataStream indexData;
        private int indexCount;

        private Vector3 boxMaxVector;
        private Vector3 boxMinVector;

        public PickHull(DataStream vertexData, int vertexCount, VertexElement[] vertexElements, DataStream indexData, int indexCount)
        {
            this.vertexData = vertexData;
            this.vertexCount = vertexCount;
            this.vertexElements = vertexElements;
            this.indexData = indexData;
            this.indexCount = indexCount;

            this.vertexElementSize = (int)vertexData.Length / vertexCount;

            this.positionElement = vertexElements.First(e => e.WellKnownFormat == VertexElement.Format.Position);
            foreach (var element in vertexElements)
            {
                if (!element.Equals(positionElement))
                    strideToPosition += element.Size;
                else
                    break;
            }

            this.Precalculate();
        }

        public bool TryPick(Ray pickRay, Matrix worldMatrix, out float distance)
        {
            distance = float.MaxValue;

            var boundingSphere = CalcBoundingSphere(worldMatrix);
            if (!Ray.Intersects(pickRay, boundingSphere, out distance))
                return false;

            distance = float.MaxValue;
            indexData.Position = 0;
		    for (var i = 0; i < indexCount / 3; ++i)
		    {
			    var triangle = new Vector3[3];
                triangle[0] = Vector3.TransformCoordinate(this.GetPositionFromData(indexData.Read<uint>()), worldMatrix);
                triangle[1] = Vector3.TransformCoordinate(this.GetPositionFromData(indexData.Read<uint>()), worldMatrix);
                triangle[2] = Vector3.TransformCoordinate(this.GetPositionFromData(indexData.Read<uint>()), worldMatrix);

                float newDistance;
                if (!Ray.Intersects(pickRay, triangle[0], triangle[1], triangle[2], out newDistance)
                    || newDistance > distance)
                    continue;
                distance = newDistance;
		    }

            return distance != float.MaxValue;
        }

        private Vector3 GetPositionFromData(uint index)
        {
            vertexData.Position = index * vertexElementSize + strideToPosition;
            return vertexData.Read<Vector3>();
        }

        protected void Precalculate()
        {
            boxMinVector = Vector3.Zero;
            boxMaxVector = Vector3.Zero;
            for (uint i = 0; i < vertexCount; ++i)
            {
                boxMinVector = i == 0 ? this.GetPositionFromData(i) : Vector3.Maximize(boxMinVector, this.GetPositionFromData(i));
                boxMaxVector = i == 0 ? this.GetPositionFromData(i) : Vector3.Minimize(boxMaxVector, this.GetPositionFromData(i));
            }
        }

        public BoundingSphere CalcBoundingSphere(Matrix worldMatrix)
        {
            var centerPosition = Vector3.TransformCoordinate(Vector3.Zero, worldMatrix);
            var maxVec = Vector3.TransformCoordinate(boxMaxVector, worldMatrix);
            return new BoundingSphere(centerPosition, maxVec.Length());
        }

        public BoundingBox CalcBoundingBox(Matrix worldMatrix)
        {
            var minVec = Vector3.TransformCoordinate(boxMinVector, worldMatrix);
            var maxVec = Vector3.TransformCoordinate(boxMaxVector, worldMatrix);
            return new BoundingBox(minVec, maxVec);
        }
    }
}