var bbox = require('@turf/bbox'),
    point = require('@turf/helpers').point;

/**
 * Takes a {@link Feature} or {@link FeatureCollection} and returns the absolute center point of all features.
 *
 * @name center
 * @param {(Feature|FeatureCollection)} layer input features
 * @return {Feature<Point>} a Point feature at the absolute center point of all input features
 * @addToMap features, centerPt
 * @example
 * var features = {
 *   "type": "FeatureCollection",
 *   "features": [
 *     {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.522259, 35.4691]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.502754, 35.463455]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.508269, 35.463245]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.516809, 35.465779]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.515372, 35.467072]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.509363, 35.463053]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.511123, 35.466601]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.518547, 35.469327]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.519706, 35.469659]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.517839, 35.466998]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.508678, 35.464942]
 *       }
 *     }, {
 *       "type": "Feature",
 *       "properties": {},
 *       "geometry": {
 *         "type": "Point",
 *         "coordinates": [-97.514914, 35.463453]
 *       }
 *     }
 *   ]
 * };
 *
 * var centerPt = turf.center(features);
 * centerPt.properties['marker-size'] = 'large';
 * centerPt.properties['marker-color'] = '#000';
 *
 * var resultFeatures = features.features.concat(centerPt);
 * var result = {
 *   "type": "FeatureCollection",
 *   "features": resultFeatures
 * };
 *
 * //=result
 */

module.exports = function (layer) {
    var ext = bbox(layer);
    var x = (ext[0] + ext[2]) / 2;
    var y = (ext[1] + ext[3]) / 2;
    return point([x, y]);
};