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

  var interpolate = function(page, expr) {
    if (!expr) {
      return null;
    }

    var inter = $interpolate(expr, true, null, true);
    if (!inter) {
      return expr.toString();
    }

    return inter(page.scope);
  };

  metaService.getTitle = function(page) {
    if (!page || !page.$$route) {
      return null;
    }

    var route = page.$$route;
    return interpolate(page, route && route.title);
  };

  metaService.getDescription = function(page) {
    return new Promise(function(resolve, reject) {
      if (!page || !page.$$route) {
        resolve(null);
      } else {
        // Timeout needed because page.scope is undefined
        $timeout(function() {
          resolve(interpolate(page, page.$$route.description));
        }, 10);
      }
    });
  };

  return metaService;
}]);