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

namespace BouncyCatIsBouncy
{
    class Physics
    {
        List<PhysicsBody> m_bodies = new List<PhysicsBody>();
        PhysicsBody m_primaryBody;

        public void Add(PhysicsBody obj)
        {
            Debug.Assert(obj != null);
            m_bodies.Add(obj);
        }
        public void SetPrimary(PhysicsBody obj)
        {
            Debug.Assert(obj != null);

            m_primaryBody = obj;
        }
        public void ClearAllSecondaries()
        {
            m_bodies.Clear();
        }
        public void ClearAll()
        {
            ClearAllSecondaries();
            m_primaryBody = null;
        }

        void ResolveCollisions(List<CollidingInfo> collisions)
        {
            foreach (var info in collisions)
            {
                if (m_primaryBody.CollisionResponseEnable && info.Body.CollisionResponseEnable)
                {
                    m_primaryBody.Position -= m_primaryBody.Velocity * info.Penetration;

                    m_primaryBody.Velocity = Vector2.Reflect(m_primaryBody.Velocity, info.Normal);
                    m_primaryBody.Position += m_primaryBody.Velocity * info.Penetration;

                    m_primaryBody.Velocity *= info.Body.CoeffRestitution * m_primaryBody.CoeffRestitution;
                }

                info.Body.Collision(m_primaryBody);
                m_primaryBody.Collision(info.Body);
            }
        }
        public void Update(float dt)
        {
            if (m_primaryBody != null)
            {
                var collidingGeoms = new List<CollidingInfo>();
                m_primaryBody.Update(dt);
                foreach (var geom in m_primaryBody.Geometry)
                {
                    foreach (var body in m_bodies)
                    {
                        body.Update(dt);
                        foreach (var otherGeom in body.Geometry)
                        {
                            CollisionInfo info = otherGeom.BroadCollides(geom);
                            if (info.Collides)
                            {
                                collidingGeoms.Add(new CollidingInfo() { Body = body, Normal = info.Normal, Penetration = info.Penetration });
                            }
                        }
                    }
                }

                if (collidingGeoms.Count > 0)
                {
                    ResolveCollisions(collidingGeoms);
                }
            }
        }

        [Conditional("DEBUG")]
        public void DebugDraw(Microsoft.Xna.Framework.Graphics.SpriteBatch batch)
        {
            foreach (var geom in m_primaryBody.Geometry)
            {
                Debugging.RadialBBRenderer.Draw(batch, (RadialBB)geom.Bounding);
            }
            foreach (var body in m_bodies)
            {
                foreach (var geom in body.Geometry)
                {
                    if (geom.Bounding is OBB)
                        Debugging.OBBRenderer.Draw(batch, (OBB)geom.Bounding);
                    else if (geom.Bounding is RadialBB)
                        Debugging.RadialBBRenderer.Draw(batch, (RadialBB)geom.Bounding);
                    
                }
            }
        }
    }
}