Пошаговое выполнение долгого скрипта (AngularJS + PHP)

index.html

<div ng-app="testApp">
	<div ng-controller="TestCtrl" ng-init="ajaxStart">
		{{progress}}
	</div>
</div>

progress.php

if(isset($_SERVER['HTTP_X_REQUESTED_WITH']) && !empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
  // Если к нам идёт Ajax запрос, то ловим его
  switch ($post['action']) {
    case 'progress':
      session_start(); 
      echo json_encode($_SESSION["progress"]);
      break;
  
    default:
      //LONG RUNNING TASK
      for($i = 1; $i <= 10; $i++) {
        session_start(); 
        $_SESSION["progress"] = ['status' => true, 'message' => "on iteration $i of 10", 'progress' => $i*10];
        session_write_close();         
        sleep(1);
      }
      unset($_SESSION["progress"]);
      echo json_encode(['status' => true, 'message' => "completed", 'stop' => true]);
      break;
  }
  exit;
}

script.js

var app = angular.module('testApp', []);
app.config(['$httpProvider', function ($httpProvider) {
  $httpProvider.defaults.headers.post['Content-Type'] = 'application/x-www-form-urlencoded; charset=UTF-8';
  /**
  * The workhorse; converts an object to x-www-form-urlencoded serialization.
  * @param {Object} obj
  * @return {String}
  */ 
  var param = function(obj) {
    var query = '', name, value, fullSubName, subName, subValue, innerObj, i;

    for(name in obj) {
      value = obj[name];

      if(value instanceof Array) {
        for(i=0; i<value.length; ++i) {
          subValue = value[i];
          fullSubName = name + '[' + i + ']';
          innerObj = {};
          innerObj[fullSubName] = subValue;
          query += param(innerObj) + '&';
        }
      }
      else if(value instanceof Object) {
        for(subName in value) {
          subValue = value[subName];
          fullSubName = name + '[' + subName + ']';
          innerObj = {};
          innerObj[fullSubName] = subValue;
          query += param(innerObj) + '&';
        }
      }
      else if(value !== undefined && value !== null)
        query += encodeURIComponent(name) + '=' + encodeURIComponent(value) + '&';
    }

    return query.length ? query.substr(0, query.length - 1) : query;
  };

  // Override $http service's default transformRequest
  $httpProvider.defaults.transformRequest = function(data) {
    return angular.isObject(data) && String(data) !== '[object File]' ? param(data) : data;
  };
}]);
app.controller('TestCtrl', ['$scope', '$http', '$timeout', '$interval', '$q', function($scope, $http, $timeout, $interval, $q) {
    $scope.ajaxStart = $timeout(function(){
        var autoUpdate, cancel = $q.defer();
        $http.post(
            'progress.php', 
            {ajax: 'Y', id: $scope.data, action: 'start'}
        ).then(function(response) {
            $scope.progress = response.data;
            if (autoUpdate) $interval.cancel(autoUpdate);
            cancel.resolve();
        }, function(response) {
            // called asynchronously if an error occurs
            // or server returns response with an error status.
        });
        autoUpdate = $interval(function(){
            console.info('проверяем статус...');
            $http.post(
                'progress.php', 
                {action: 'progress'},
                {timeout: cancel.promise}
            ).then(function(response) {
                $scope.progress = response.data;
            });
        }, 1000);
    }, 100);
}]);