/**
                                * The `Matter.Detector` module contains methods for efficiently detecting collisions between a list of bodies using a broadphase algorithm.
                                *
                                * @class Detector
                                */
                                
                                var Detector = {};
                                
                                module.exports = Detector;
                                
                                var Common = require('../core/Common');
                                var Collision = require('./Collision');
                                
                                (function() {
                                
                                    /**
                                     * Creates a new collision detector.
                                     * @method create
                                     * @param {} options
                                     * @return {detector} A new collision detector
                                     */
                                    Detector.create = function(options) {
                                        var defaults = {
                                            bodies: [],
                                            pairs: null
                                        };
                                
                                        return Common.extend(defaults, options);
                                    };
                                
                                    /**
                                     * Sets the list of bodies in the detector.
                                     * @method setBodies
                                     * @param {detector} detector
                                     * @param {body[]} bodies
                                     */
                                    Detector.setBodies = function(detector, bodies) {
                                        detector.bodies = bodies.slice(0);
                                    };
                                
                                    /**
                                     * Clears the detector including its list of bodies.
                                     * @method clear
                                     * @param {detector} detector
                                     */
                                    Detector.clear = function(detector) {
                                        detector.bodies = [];
                                    };
                                
                                    /**
                                     * Efficiently finds all collisions among all the bodies in `detector.bodies` using a broadphase algorithm.
                                     * 
                                     * _Note:_ The specific ordering of collisions returned is not guaranteed between releases and may change for performance reasons.
                                     * If a specific ordering is required then apply a sort to the resulting array.
                                     * @method collisions
                                     * @param {detector} detector
                                     * @return {collision[]} collisions
                                     */
                                    Detector.collisions = function(detector) {
                                        var collisions = [],
                                            pairs = detector.pairs,
                                            bodies = detector.bodies,
                                            bodiesLength = bodies.length,
                                            canCollide = Detector.canCollide,
                                            collides = Collision.collides,
                                            i,
                                            j;
                                
                                        bodies.sort(Detector._compareBoundsX);
                                
                                        for (i = 0; i < bodiesLength; i++) {
                                            var bodyA = bodies[i],
                                                boundsA = bodyA.bounds,
                                                boundXMax = bodyA.bounds.max.x,
                                                boundYMax = bodyA.bounds.max.y,
                                                boundYMin = bodyA.bounds.min.y,
                                                bodyAStatic = bodyA.isStatic || bodyA.isSleeping,
                                                partsALength = bodyA.parts.length,
                                                partsASingle = partsALength === 1;
                                
                                            for (j = i + 1; j < bodiesLength; j++) {
                                                var bodyB = bodies[j],
                                                    boundsB = bodyB.bounds;
                                
                                                if (boundsB.min.x > boundXMax) {
                                                    break;
                                                }
                                
                                                if (boundYMax < boundsB.min.y || boundYMin > boundsB.max.y) {
                                                    continue;
                                                }
                                
                                                if (bodyAStatic && (bodyB.isStatic || bodyB.isSleeping)) {
                                                    continue;
                                                }
                                
                                                if (!canCollide(bodyA.collisionFilter, bodyB.collisionFilter)) {
                                                    continue;
                                                }
                                
                                                var partsBLength = bodyB.parts.length;
                                
                                                if (partsASingle && partsBLength === 1) {
                                                    var collision = collides(bodyA, bodyB, pairs);
                                
                                                    if (collision) {
                                                        collisions.push(collision);
                                                    }
                                                } else {
                                                    var partsAStart = partsALength > 1 ? 1 : 0,
                                                        partsBStart = partsBLength > 1 ? 1 : 0;
                                                    
                                                    for (var k = partsAStart; k < partsALength; k++) {
                                                        var partA = bodyA.parts[k],
                                                            boundsA = partA.bounds;
                                
                                                        for (var z = partsBStart; z < partsBLength; z++) {
                                                            var partB = bodyB.parts[z],
                                                                boundsB = partB.bounds;
                                
                                                            if (boundsA.min.x > boundsB.max.x || boundsA.max.x < boundsB.min.x
                                                                || boundsA.max.y < boundsB.min.y || boundsA.min.y > boundsB.max.y) {
                                                                continue;
                                                            }
                                
                                                            var collision = collides(partA, partB, pairs);
                                
                                                            if (collision) {
                                                                collisions.push(collision);
                                                            }
                                                        }
                                                    }
                                                }
                                            }
                                        }
                                
                                        return collisions;
                                    };
                                
                                    /**
                                     * Returns `true` if both supplied collision filters will allow a collision to occur.
                                     * See `body.collisionFilter` for more information.
                                     * @method canCollide
                                     * @param {} filterA
                                     * @param {} filterB
                                     * @return {bool} `true` if collision can occur
                                     */
                                    Detector.canCollide = function(filterA, filterB) {
                                        if (filterA.group === filterB.group && filterA.group !== 0)
                                            return filterA.group > 0;
                                
                                        return (filterA.mask & filterB.category) !== 0 && (filterB.mask & filterA.category) !== 0;
                                    };
                                
                                    /**
                                     * The comparison function used in the broadphase algorithm.
                                     * Returns the signed delta of the bodies bounds on the x-axis.
                                     * @private
                                     * @method _sortCompare
                                     * @param {body} bodyA
                                     * @param {body} bodyB
                                     * @return {number} The signed delta used for sorting
                                     */
                                    Detector._compareBoundsX = function(bodyA, bodyB) {
                                        return bodyA.bounds.min.x - bodyB.bounds.min.x;
                                    };
                                
                                    /*
                                    *
                                    *  Properties Documentation
                                    *
                                    */
                                
                                    /**
                                     * The array of `Matter.Body` between which the detector finds collisions.
                                     * 
                                     * _Note:_ The order of bodies in this array _is not fixed_ and will be continually managed by the detector.
                                     * @property bodies
                                     * @type body[]
                                     * @default []
                                     */
                                
                                    /**
                                     * Optional. A `Matter.Pairs` object from which previous collision objects may be reused. Intended for internal `Matter.Engine` usage.
                                     * @property pairs
                                     * @type {pairs|null}
                                     * @default null
                                     */
                                
                                })();