const cache = Symbol('cache');

const SECOND = 1000;
const MINUTE = SECOND * 60;
const HOUR = MINUTE * 60;
const DAY = HOUR * 24;

exports = module.exports = class Cache {
    constructor() {
        this.defaultTime = HOUR;
        this[cache] = {};
        setInterval(() => {
            let list = Object.keys(this[cache]);
            let now = Date.now();
            list.forEach(key => {
                // 因为是单线程的，所以不用担心这个处理完之前有其它线程把 key 清理掉
                let time = this[cache][key].time;
                if (time && time <= now) {
                    this.del(key);
                }
            });
        }, HOUR + MINUTE * 20);  // 与默认超时时间不同，防止雪崩
    }

    setItem(key, value, opts) {
        if (key === undefined || value === undefined) {
            console.warn(`key: ${key} or value: ${value} undefined!`);
            return;
        }
        let time = this.defaultTime;
        if (opts && opts.time) {
            time = opts.time;
        }
        this[cache][key] = {
            data: value,
            time: +Date.now() + time
        }

        return this;
    }

    getItem(key) {
        let now = Date.now();
        if (this[cache][key]) {
            if (this[cache][key].time >= now) {
                return this[cache][key].data;
            }
            else {
                this.delItem(key);
            }
        }
        return null;
    }

    delItem(key) {
        delete this[cache][key];
        return this;
    }

    getLength() {
        return Object.keys(this[cache]).length;
    }

    clear() {
        this[cache] = {};
    }
}