8. $http, promises and $q

app.factory("productApi", ["$http", "$q", function ($http, $q) {
  const cache = {};
  return {
    get(id) {
      if (cache[id]) return $q.resolve(cache[id]);          // $q promise, integrates with the digest
      return $http.get(`/api/products/${id}`, { timeout: 10000 })
        .then(res => (cache[id] = res.data))
        .catch(err => $q.reject(err.status === 404 ? "Not found" : "Server error"));
    },
    all: ids => $q.all(ids.map(id => this.get(id))),
  };
}]);

// Interceptor: add auth header and handle 401 globally
app.factory("authInterceptor", ["$q", "$window", function ($q, $window) {
  return {
    request: config => { config.headers.Authorization = `Bearer ${$window.sessionStorage.token}`; return config; },
    responseError: rejection => { if (rejection.status === 401) $window.location = "/login"; return $q.reject(rejection); },
  };
}]);
app.config(["$httpProvider", $httpProvider => $httpProvider.interceptors.push("authInterceptor")]);