leo-cache/index.js

Cache for the Leo Platform

'use strict';

let cache = {};
const expireDefault = 1 * 60 * 1000;
async function refresh(name, func) {
    let c = cache[name];
    if (c.onRefresh) { //someone is already trying to refresh it
        return new Promise((resolve, reject) => {
            c.onRefresh.listeners.push(() => {
                resolve(true);
            });
        });
    } else {
        c.onRefresh = {
            start: Date.now(),
            listeners: []
        };
        let v = await func(name);
        cache[name] = {
            ts: Date.now(),
            v: v,
            shouldRefresh: false,
            refreshing: []
        };
        if (c.onRefresh && c.onRefresh.listeners.length) {
            c.onRefresh.listeners.map(f => f());
        }
        return true;
    }
}

function getFromCache(name, expireDuration, overlyStaleDuration) {
    //Does it exist
    if (!(name in cache)) {
        cache[name] = {
            ts: 0,
            v: null,
            shouldRefresh: false,
            refreshing: []
        };
        return false;
    } else {
        let c = cache[name];
        let staleDuration = Date.now() - c.ts;
        let isExpired = c.ts === 0 || staleDuration >= expireDuration;
        if (isExpired) {
            let isOverlyStale = c.ts === 0 || staleDuration >= overlyStaleDuration;
            if (isOverlyStale) {
                return false;
            } else {
                c.shouldRefresh = true;
                return c;
            }
        } else {
            return c;
        }
    }
}
module.exports = {
    get: async function(name, func, expireDuration = expireDefault, opts = {}) {
        opts = Object.assign({
            allowedStalePeriod: 0,
            maxRefreshWait: 10 * 1000
        }, opts);
        let overlyStaleDuration = expireDuration + opts.allowedStalePeriod;
        let r = getFromCache(name, expireDuration, overlyStaleDuration);
        //No cache
        if (r === false) {
            await refresh(name, func);
        } else if (r.shouldRefresh == true) { //It is there but getting stale
            refresh(name, func);
        }
        return cache[name].v;
    }
};