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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
// This should be slightly less than SYSTEM_TICK_INTERVAL as timer
// comparisons are too exact while the async/await functionality will make the
// last recorded time a little bit later. This causes the comparasion to skip
// updates.
// It should be 10% less than SYSTEM_TICK to update at least once every 5 mins.
const EXPIRATION_TIME = 4.5 * 60 * 1000; // 4.5 minutes
/**
* Cache link results from a provided object property and refresh after some
* amount of time has passed. Allows for migrating data from previously cached
* links to the new links with the same url.
*/
export class LinksCache {
/**
* Create a links cache for a given object property.
*
* @param {object} linkObject Object containing the link property
* @param {string} linkProperty Name of property on object to access
* @param {array} properties Optional properties list to migrate to new links.
* @param {function} shouldRefresh Optional callback receiving the old and new
* options to refresh even when not expired.
*/
constructor(
linkObject,
linkProperty,
properties = [],
shouldRefresh = () => {}
) {
this.clear();
// Allow getting links from both methods and array properties
this.linkGetter = options => {
const ret = linkObject[linkProperty];
return typeof ret === "function" ? ret.call(linkObject, options) : ret;
};
// Always migrate the shared cache data in addition to any custom properties
this.migrateProperties = ["__sharedCache", ...properties];
this.shouldRefresh = shouldRefresh;
}
/**
* Clear the cached data.
*/
clear() {
this.cache = Promise.resolve([]);
this.lastOptions = {};
this.expire();
}
/**
* Force the next request to update the cache.
*/
expire() {
delete this.lastUpdate;
}
/**
* Request data and update the cache if necessary.
*
* @param {object} options Optional data to pass to the underlying method.
* @returns {promise(array)} Links array with objects that can be modified.
*/
async request(options = {}) {
// Update the cache if the data has been expired
const now = Date.now();
if (
this.lastUpdate === undefined ||
now > this.lastUpdate + EXPIRATION_TIME ||
// Allow custom rules around refreshing based on options
this.shouldRefresh(this.lastOptions, options)
) {
// Update request state early so concurrent requests can refer to it
this.lastOptions = options;
this.lastUpdate = now;
// Save a promise before awaits, so other requests wait for correct data
// eslint-disable-next-line no-async-promise-executor
this.cache = new Promise(async (resolve, reject) => {
try {
// Allow fast lookup of old links by url that might need to migrate
const toMigrate = new Map();
for (const oldLink of await this.cache) {
if (oldLink) {
toMigrate.set(oldLink.url, oldLink);
}
}
// Update the cache with migrated links without modifying source objects
resolve(
(await this.linkGetter(options)).map(link => {
// Keep original array hole positions
if (!link) {
return link;
}
// Migrate data to the new link copy if we have an old link
const newLink = Object.assign({}, link);
const oldLink = toMigrate.get(newLink.url);
if (oldLink) {
for (const property of this.migrateProperties) {
const oldValue = oldLink[property];
if (oldValue !== undefined) {
newLink[property] = oldValue;
}
}
} else {
// Share data among link copies and new links from future requests
newLink.__sharedCache = {};
}
// Provide a helper to update the cached link
newLink.__sharedCache.updateLink = (property, value) => {
newLink[property] = value;
};
return newLink;
})
);
} catch (error) {
reject(error);
}
});
}
// Provide a shallow copy of the cached link objects for callers to modify
return (await this.cache).map(link => link && Object.assign({}, link));
}
}