'use strict'
/**
 * Copyright (c) 2017~2019, OBCon Inc.
 * All rights reserved.
 */

/**
 * @file
 * @copyright 2017~2019, OBCon Inc.
 * @author gye hyun james kim [pnuskgh@gmail.com]
 */

let moment = require('moment');

//--- 일반적으로 LRU가 LFU보다 우수함
//--- LRU (Least Recently Used, 가장 최근 사용) : 가장 오래된 것 삭제
//--- LFU (Least Frequently Used, 최소 빈도 사용) : 참조 횟수가 가장 작은 것 삭제
class Cache {
    constructor(capacity, isLFU=true) {
        this.isLFU = isLFU;

        this.capacity = capacity;
        this.size = 0;

        this.cacheDataset = {};                             //--- Cache 데이터 저장
        // this.cacheFreq = {};                                //--- Cache 사용 빈도 저장 for LFU          -> To-Do: Linked List
        this.cacheDatetime = {};                            //--- Cache의 최근 접근일시 저장 for LRU     -> To-Do: Linked List
        this.size = 0;
    }

    getCache(key) {
        if (this.existCache(key)) {
            // this.cacheFreq[key] = this.cacheFreq[key] + 1;
            this.cacheDatetime[key] = moment();
            return this.cacheDataset[key];
        }
        return null;
    }

    setCache(key, value) {
        this.cacheDataset[key] = value;
        // this.cacheFreq[key] = (this.existCache(key)) ? this.cacheFreq[key] + 1:1;
        this.cacheDatetime[key] = moment();
    }

    existCache(key) {
        return this.cacheDataset.hasOwnProperty(key);
    }

    delCache(key) {
        if (this.existCache(key)) {
            delete this.cacheDataset[key];
            // delete this.cacheFreq[key];
            delete this.cacheDatetime[key];
            this.size = this.size - 1;
        }
    }
}

module.exports = Cache;