var Util = {};

Util.getContextID = function(ctx) {
  return [ctx.zoom, ctx.tile.x, ctx.tile.y].join(":");
};

/**
 * Default function that gets the id for a layer feature.
 * Sometimes this needs to be done in a different way and
 * can be specified by the user in the options for L.TileLayer.MVTSource.
 *
 * @param feature
 * @returns {ctx.id|*|id|string|jsts.index.chain.MonotoneChain.id|number}
 */
Util.getIDForLayerFeature = function(feature) {
  return feature.properties.id;
};

Util.getJSON = function(url, callback) {
  var xmlhttp = typeof XMLHttpRequest !== 'undefined' ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
  xmlhttp.onreadystatechange = function() {
    var status = xmlhttp.status;
    if (xmlhttp.readyState === 4 && status >= 200 && status < 300) {
      var json = JSON.parse(xmlhttp.responseText);
      callback(null, json);
    } else {
      callback( { error: true, status: status } );
    }
  };
  xmlhttp.open("GET", url, true);
  xmlhttp.send();
};