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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;
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