/**
 * System takes care of updating all the entities (based on their component data)
 * @param apiSystem GameLib.API.System
 * @constructor
 */
GameLib.System.Physics = function(
    apiSystem
) {

    GameLib.System.call(
        this,
        apiSystem
    );

    this.worldSubscription = null;
    this.rigidBodySubscription = null;
};

GameLib.System.Physics.prototype = Object.create(GameLib.System.prototype);
GameLib.System.Physics.prototype.constructor = GameLib.System.Physics;

GameLib.System.Physics.prototype.updateWorlds = function() {
    this.worlds = GameLib.EntityManager.Instance.query(
        [
            GameLib.D3.World
        ]
    );
};

GameLib.System.Physics.prototype.updateRigidBodies = function() {
    this.rigidBodyEntities = GameLib.EntityManager.Instance.query(
        [
            GameLib.D3.RigidBody
        ]
    );
};

GameLib.System.Physics.prototype.start = function() {

    this.worldSubscription = this.subscribe(
        GameLib.Event.WORLD_INSTANCE_CREATED,
        this.updateWorlds
    );

    this.rigidBodySubscription = this.subscribe(
        GameLib.Event.RIGID_BODY_INSTANCE_CREATED,
        this.updateRigidBodies
    );

    this.updateWorlds();

    this.updateRigidBodies();

};

/**
 * Update script
 */
GameLib.System.Physics.prototype.update = function() {

    /**
     * TODO: progress the world according to delta time
     */
    this.worlds.map(function(
        world
    ){
        world.step(1 / 60.0);
    });

	this.rigidBodyEntities.map(

		function (rigidBody) {

            /**
             * TODO: update mesh position based on rigidbody position
             */
		}
	);

};

GameLib.System.Physics.prototype.stop = function() {

    this.worlds = [];
	this.rigidBodyEntities	= [];

	if (this.worldSubscription) {
        this.worldSubscription.remove();
    }

    if (this.rigidBodySubscription) {
        this.rigidBodySubscription.remove();
    }
};