// @if DEBUG
                        /**
                        * _Internal Class_, not generally used outside of the engine's internals.
                        *
                        */
                        
                        var Metrics = {};
                        
                        module.exports = Metrics;
                        
                        var Composite = require('../body/Composite');
                        var Common = require('./Common');
                        
                        (function() {
                        
                            /**
                             * Creates a new metrics.
                             * @method create
                             * @private
                             * @return {metrics} A new metrics
                             */
                            Metrics.create = function(options) {
                                var defaults = {
                                    extended: false,
                                    narrowDetections: 0,
                                    narrowphaseTests: 0,
                                    narrowReuse: 0,
                                    narrowReuseCount: 0,
                                    midphaseTests: 0,
                                    broadphaseTests: 0,
                                    narrowEff: 0.0001,
                                    midEff: 0.0001,
                                    broadEff: 0.0001,
                                    collisions: 0,
                                    buckets: 0,
                                    bodies: 0,
                                    pairs: 0
                                };
                        
                                return Common.extend(defaults, false, options);
                            };
                        
                            /**
                             * Resets metrics.
                             * @method reset
                             * @private
                             * @param {metrics} metrics
                             */
                            Metrics.reset = function(metrics) {
                                if (metrics.extended) {
                                    metrics.narrowDetections = 0;
                                    metrics.narrowphaseTests = 0;
                                    metrics.narrowReuse = 0;
                                    metrics.narrowReuseCount = 0;
                                    metrics.midphaseTests = 0;
                                    metrics.broadphaseTests = 0;
                                    metrics.narrowEff = 0;
                                    metrics.midEff = 0;
                                    metrics.broadEff = 0;
                                    metrics.collisions = 0;
                                    metrics.buckets = 0;
                                    metrics.pairs = 0;
                                    metrics.bodies = 0;
                                }
                            };
                        
                            /**
                             * Updates metrics.
                             * @method update
                             * @private
                             * @param {metrics} metrics
                             * @param {engine} engine
                             */
                            Metrics.update = function(metrics, engine) {
                                if (metrics.extended) {
                                    var world = engine.world,
                                        bodies = Composite.allBodies(world);
                        
                                    metrics.collisions = metrics.narrowDetections;
                                    metrics.pairs = engine.pairs.list.length;
                                    metrics.bodies = bodies.length;
                                    metrics.midEff = (metrics.narrowDetections / (metrics.midphaseTests || 1)).toFixed(2);
                                    metrics.narrowEff = (metrics.narrowDetections / (metrics.narrowphaseTests || 1)).toFixed(2);
                                    metrics.broadEff = (1 - (metrics.broadphaseTests / (bodies.length || 1))).toFixed(2);
                                    metrics.narrowReuse = (metrics.narrowReuseCount / (metrics.narrowphaseTests || 1)).toFixed(2);
                                    //var broadphase = engine.broadphase[engine.broadphase.current];
                                    //if (broadphase.instance)
                                    //    metrics.buckets = Common.keys(broadphase.instance.buckets).length;
                                }
                            };
                        
                        })();
                        // @endif