/* Sparx
 * Copyright August Zinsser 2007
 * This program is distributed under the terms of the GNU General Public License
 */


using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Xna.Framework;


namespace Pina3D.Particles
{
    public class Gravitational : Force
    {
        private Emitter mCenter;
        private Vector3 mCentralDisplacement;

        public Emitter Center { set { mCenter = value; } get { return mCenter; } }
        /// <summary>
        /// Displaces the center of gravity from the central object by this amount
        /// </summary>
        public Vector3 CentralDisplacement { set { mCentralDisplacement = value; } get { return mCentralDisplacement; } }


        public Gravitational(string name, float lifeSpan, float delay, Emitter center, Vector3 centralDisplacement, float magnitude)
            : base (name, lifeSpan, delay)
        {
            mCenter = center;
            mMagnitude = magnitude;
            mCentralDisplacement = centralDisplacement;
        }


        public override Object Clone()
        {
            Gravitational retFo = new Gravitational(mName + "_clone", mAge, mDelay, mCenter, mCentralDisplacement, mMagnitude);
            return retFo;
        }


        public override void Update(Emission emission)
        {
            if (mCenter != null && emission.Age > mDelay && emission.Age < mLifeExpectancy + mDelay)
            {
                RecalculateForceVector(emission);
                emission.Velocity3D += Vector3.Multiply(mForceVector, Pina.ElapsedSeconds);
            }
        }


        /// <summary>
        /// Makes a force vector that points from this emission to the center
        /// </summary>
        /// <param name="emission"></param>
        private void RecalculateForceVector(Emission newCenter)
        {
            // Doing real gravity makes it freak out a bit, and it looks cooler without it... so do it without real gravity!
            mForceVector = mCenter.Position3D + mCentralDisplacement - newCenter.Position3D;
            //float distanceSquared = (float)mForceVector.LengthSquared();
            mForceVector.Normalize();
            //mForceVector = Vector2.Multiply(mForceVector, mMagnitude * (1 / distanceSquared));
            mForceVector = Vector3.Multiply(mForceVector, mMagnitude);
        }
    }
}