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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+/**
+ * A middleware which acts like a service, because it is stateful
+ * and "long-running" in the background. It provides the ability
+ * for actions to install a function to be run once when a specific
+ * condition is met by an action coming through the system. Think of
+ * it as a thunk that blocks until the condition is met. Example:
+ *
+ * ```js
+ * const services = { WAIT_UNTIL: require('wait-service').NAME };
+ *
+ * { type: services.WAIT_UNTIL,
+ * predicate: action => action.type === constants.ADD_ITEM,
+ * run: (dispatch, getState, action) => {
+ * // Do anything here. You only need to accept the arguments
+ * // if you need them. `action` is the action that satisfied
+ * // the predicate.
+ * }
+ * }
+ * ```
+ */
+const NAME = exports.NAME = "@@service/waitUntil";
+
+function waitUntilService({ dispatch, getState }) {
+ let pending = [];
+
+ function checkPending(action) {
+ let readyRequests = [];
+ let stillPending = [];
+
+ // Find the pending requests whose predicates are satisfied with
+ // this action. Wait to run the requests until after we update the
+ // pending queue because the request handler may synchronously
+ // dispatch again and run this service (that use case is
+ // completely valid).
+ for (let request of pending) {
+ if (request.predicate(action)) {
+ readyRequests.push(request);
+ } else {
+ stillPending.push(request);
+ }
+ }
+
+ pending = stillPending;
+ for (let request of readyRequests) {
+ request.run(dispatch, getState, action);
+ }
+ }
+
+ return next => action => {
+ if (action.type === NAME) {
+ pending.push(action);
+ return null;
+ }
+ let result = next(action);
+ checkPending(action);
+ return result;
+ };
+}
+exports.waitUntilService = waitUntilService;