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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
"use strict";
const {
BATCH_ACTIONS,
BATCH_ENABLE,
BATCH_RESET,
BATCH_FLUSH,
const REQUESTS_REFRESH_RATE = 50; // ms
/**
* Middleware that watches for actions with a "batch = true" value in their meta field.
* These actions are queued and dispatched as one batch after a timeout.
* Special actions that are handled by this middleware:
* - BATCH_ENABLE can be used to enable and disable the batching.
* - BATCH_RESET discards the actions that are currently in the queue.
*/
function batchingMiddleware() {
return next => {
let queuedActions = [];
let enabled = true;
let flushTask = null;
return action => {
if (action.type === BATCH_ENABLE) {
return setEnabled(action.enabled);
}
if (action.type === BATCH_RESET) {
return resetQueue();
}
if (action.type === BATCH_FLUSH) {
return flushQueue();
}
if (action.meta?.batch) {
if (!enabled) {
next(action);
return Promise.resolve();
}
queuedActions.push(action);
if (!flushTask) {
flushTask = new DelayedTask(flushActions, REQUESTS_REFRESH_RATE);
}
return flushTask.promise;
}
return next(action);
};
function setEnabled(value) {
enabled = value;
// If disabling the batching, flush the actions that have been queued so far
if (!enabled && flushTask) {
flushTask.runNow();
}
}
function resetQueue() {
queuedActions = [];
if (flushTask) {
flushTask.cancel();
flushTask = null;
}
}
function flushQueue() {
if (flushTask) {
flushTask.runNow();
}
}
function flushActions() {
const actions = queuedActions;
queuedActions = [];
next({
type: BATCH_ACTIONS,
actions,
});
flushTask = null;
}
};
}
/**
* Create a delayed task that calls the specified task function after a delay.
*/
function DelayedTask(taskFn, delay) {
this._promise = new Promise((resolve, reject) => {
this.runTask = cancel => {
if (cancel) {
reject("Task cancelled");
} else {
taskFn();
resolve();
}
this.runTask = null;
};
this.timeout = setTimeout(this.runTask, delay);
}).catch(console.error);
}
DelayedTask.prototype = {
/**
* Return a promise that is resolved after the task is performed or canceled.
*/
get promise() {
return this._promise;
},
/**
* Cancel the execution of the task.
*/
cancel() {
clearTimeout(this.timeout);
if (this.runTask) {
this.runTask(true);
}
},
/**
* Execute the scheduled task immediately, without waiting for the timeout.
* Resolves the promise correctly.
*/
runNow() {
clearTimeout(this.timeout);
if (this.runTask) {
this.runTask();
}
},
};
module.exports = batchingMiddleware;