/**
 * Service which helps set the contents of the <meta> tags (and the <title> of a page).
 */
angular.module('quay').factory('MetaService', ['$interpolate', 'Config', '$rootScope', '$interval',
    function($interpolate, Config, $rootScope, $interval) {
  var metaService = {};
  var intervals = [];

  var interpolate = function(page, expr, callback) {
    var previous = '';

    var currentInterval = $interval(function() {
      var inter = $interpolate(expr, true, null, true);
      var result = inter(page.scope)

      if (previous && result != previous) {
        $interval.cancel(currentInterval);
      }

      previous = result;
      callback(result);
    }, 500);

    intervals.push(currentInterval);
  };

  var initial = function(value, default_value, callback) {
    for (var i = 0; i < intervals.length; ++i) {
      $interval.cancel(intervals[i]);
    }

    intervals = [];

    if (!value) {
      callback(default_value);
      return;
    }

    if (value.indexOf('{{') < 0) {
      callback(default_value);
      return;
    }

    callback('Loading...');
  };

  metaService.getInitialTitle = function(page, callback) {
    var route = page.$$route;
    initial(route && route.title, Config.REGISTRY_TITLE_SHORT, callback);
  };

  metaService.getInitialDescription = function(page, callback) {
    var route = page.$$route;
    initial(route && route.description, Config.REGISTRY_TITLE_SHORT, callback);
  };

  metaService.getTitle = function(page, callback) {
    var route = page.$$route;
    if (!route || !route.title || route.title.indexOf('{{') < 0) {
      return;
    }

    interpolate(page, route.title, callback);
  };

  metaService.getDescription = function(page, callback) {
    var route = page.$$route;
    if (!route || !route.description || route.description.indexOf('{{') < 0) {
      return;
    }

    interpolate(page, route.description, callback);
  };

  return metaService;
}]);