using System;

using Microsoft.ParallelArrays;
using FPA = Microsoft.ParallelArrays.FloatParallelArray;
using PA  = Microsoft.ParallelArrays.ParallelArrays;

namespace Bodies
{
    public class Test : IDisposable
    {
        public float[] xPos { get; private set; }
        public float[] yPos { get; private set; }
        public float[] xVel { get; private set; }
        public float[] yVel { get; private set; }
        public float[] mass { get; private set; }

        public float dec = 0.9999f;
        public float g = 1.0f;

        DX9Target target;

        public int n { get; private set; }

        public Test(int n)
        {
            target = new DX9Target();

            this.n = n;
            Random r = new Random();

            xPos = new float[n];
            yPos = new float[n];
            xVel = new float[n];
            yVel = new float[n];
            mass = new float[n];

            for (int i = 0; i < n; i++)
            {
                xPos[i] = r.Next(-100, 100);
                yPos[i] = r.Next(-100, 100);
                xVel[i] = r.Next(-10, 10);
                yVel[i] = r.Next(-10, 10);
                mass[i] = (float)(r.NextDouble() + 0.5);
            }
        }

        public void Dispose()
        {
            target.Dispose();
        }

        public void Tick()
        {
            FPA fxPos = new FPA(xPos);
            FPA fyPos = new FPA(yPos);
            FPA fxVel = new FPA(xVel);
            FPA fyVel = new FPA(yVel);
            FPA fMass = new FPA(mass);

            float[] xUpd = new float[n]; // x-update for velocity
            float[] yUpd = new float[n]; // y-update for velocity

            for (int i = 0; i < n; i++)
            {
                // x- and y-pos about point i:
                FPA ixPos = PA.Subtract(fxPos, xPos[i]);
                FPA iyPos = PA.Subtract(fyPos, yPos[i]);

                // radius from point i:
                FPA iRad = PA.Sqrt(PA.Add(PA.Multiply(ixPos, ixPos), PA.Multiply(iyPos, iyPos)));

                // x- and y-pos are now unit vectors:
                ixPos = PA.Divide(ixPos, iRad);
                iyPos = PA.Divide(iyPos, iRad);

                // vectors are now scaled by mass:
                ixPos = PA.Multiply(fMass, ixPos);
                iyPos = PA.Multiply(fMass, iyPos);

                // vectors are now scaled by G and deceleration:
                ixPos = PA.Multiply(dec * g, ixPos);
                iyPos = PA.Multiply(dec * g, iyPos);

                // sum to get ith update value:
                xUpd[i] = target.ToArray1D(PA.Sum(ixPos))[0];
                yUpd[i] = target.ToArray1D(PA.Sum(iyPos))[0];
            }

            FPA fxUpd = new FPA(xUpd);
            FPA fyUpd = new FPA(yUpd);

            // update velocities:
            fxVel = PA.Add(fxUpd, fxVel);
            fyVel = PA.Add(fyUpd, fyVel);

            // update positions:
            fxPos = PA.Add(fxVel, fxPos);
            fyPos = PA.Add(fyVel, fyPos);

            xPos = target.ToArray1D(fxPos);
            yPos = target.ToArray1D(fyPos);
            xVel = target.ToArray1D(fxVel);
            yVel = target.ToArray1D(fyVel);
        }
    }
}