somod-chat-service/build/lib/cache.js

Serverless Chat Service from SOMOD

export const cache = (max, ttl) => {
    const cacheTtl = ttl;
    const nodes = {};
    let first = undefined;
    let last = undefined;
    let size = 0;
    const remove = (key) => {
        const node = nodes[key];
        if (node.next) {
            node.next.previous = node.previous;
        }
        else {
            last = node.previous?.content.key;
        }
        if (node.previous) {
            node.previous.next = node.next;
        }
        else {
            first = node.next?.content.key;
        }
        size--;
        delete nodes[key];
    };
    const add = (key, value) => {
        const node = {
            content: {
                key,
                cachedAt: Date.now(),
                value
            }
        };
        nodes[key] = node;
        size++;
        if (first) {
            node.next = nodes[first];
            nodes[first].previous = node;
        }
        first = key;
    };
    const get = async (key, fetcher, ttl) => {
        const node = nodes[key];
        let value = node?.content.value;
        const now = Date.now();
        if (node === undefined ||
            (ttl && node.content.cachedAt < now - ttl) ||
            (cacheTtl && node.content.cachedAt < now - cacheTtl)) {
            value = await fetcher();
        }
        if (node) {
            remove(node.content.key);
        }
        add(key, value);
        if (size > max && last) {
            remove(last);
        }
        return value;
    };
    return {
        get
    };
};