How can I implement caching in angularJs factory?

angular.module('as.admin')
        .factory('userAnalyticsData',userAnalyticsData);

    userAnalyticsData.$inject = ['$http'];
    function userAnalyticsData($http) {
        var service = {
            getData: getData
        };

        var analyticsData = {};
        var called=false;
        var unCalledCallbacks=[];

        return service;


        function getData(data,callback) {

            if(!data){
                if(callback) callback(false); return;
            }


            if(called==true){
                if(!angular.equals(analyticsData, {}) && unCalledCallbacks.length==0){
                    if(callback)callback(analyticsData); return;
                }
                if(callback){
                    unCalledCallbacks.push(callback);
                }
            }

            if(!called){
                called=true;
                $http({
                    method: 'POST',
                    url : './admin/analytics',
                    data:data
                }).then(function(res){
                    if(res &&  res.data  && res.data.success==1){
                        analyticsData=res.data;
                        if(callback) callback(analyticsData);

                        if(unCalledCallbacks){
                            var i=0;
                            while (i < unCalledCallbacks.length) {
                                if (unCalledCallbacks[i]) {
                                    unCalledCallbacks[i](analyticsData);
                                    unCalledCallbacks.splice(i, 1);
                                } else {
                                  ++i;
                                }
                            }

                        }

                    }
                    else{
                        if(callback) callback(false);
                    }
                });
            }

        }
    
    }
})();