"use strict";
const EventEmitter = require('events');
const ONE_MINUTE_MS = 60 * 1000
const FIFTEEN_MINUTES_MS = 15 * 60 * 1000;
const ONE_PERCENT_RATIO = 1.01;
/**
* @abstract
* @public
*/
class Storage extends EventEmitter
{
/**
* @param {StorageOptions} options see fields
*/
constructor(options)
{
super();
/**
* id field of record
*/
this.primaryKey = options.primaryKey || 'id';
/**
* Connection string for storage. e.g. for FSStorage, it is a path
*/
this.connectionString = options.connectionString || '';
/**
* Name of collection. Derived from connection string if there is # based seperation.
*/
this.collectionName = this.connectionString.substr(this.connectionString.indexOf('#') + 1);
this.connectionString = this.connectionString.substr(0, this.connectionString.indexOf('#'));
if (!this.connectionString)
{
delete this.connectionString;
}
/**
* Minimum duration between updates in ms
* @type {number}
*/
this.updateInterval = options.updateInterval || ONE_MINUTE_MS;
/**
* Maximum duration between updates in ms
* @type {number}
*/
this.updateIntervalMax = options.updateIntervalMax || FIFTEEN_MINUTES_MS;
/**
* Rate at which update checks are slowed down when there are no updates.
* @type {number}
*/
this.updateIntervalSlowdownRate = options.updateIntervalSlowdownRate || ONE_PERCENT_RATIO;
}
/**
* Connect to data storage
*/
async connect()
{
}
/**
* @return {Array<Record>}
* @abstract
*/
async readAllRecords()
{
throw new Error('TODO: not immplemented');
}
/**
* @abstract
*/
async createRecord(record)
{
throw new Error('TODO: not immplemented');
}
/**
* @abstract
*/
async readRecord(record)
{
throw new Error('TODO: not immplemented');
}
/**
* @abstract
*/
async updateRecord(record)
{
throw new Error('TODO: not immplemented');
}
/**
* @abstract
*/
async deleteRecord(record)
{
throw new Error('TODO: not immplemented');
}
/**
* Start checking for updates.
* Emit events when there are updates.
* Required for use with CachedCollection
*/
startRecordUpdateCheck()
{
let currentTimeout = this.updateInterval;
async function checkUpdate()
{
/**
* update check timeout object
*/
this.timeout = undefined;
let updated = false;
try
{
updated = await this.updateCheckImpl();
}
catch (e)
{
console.error(e);
}
if (updated || !this.updateIntervalSlowdownRate)
{
currentTimeout = this.updateInterval;
}
else
{
currentTimeout = Math.min(currentTimeout * this.updateIntervalSlowdownRate, this.updateIntervalMax);
}
this.timeout = setTimeout(checkUpdate.bind(this), currentTimeout)
.unref();
}
this.timeout = setTimeout(checkUpdate.bind(this), currentTimeout)
.unref();
}
/**
* Implmentation of update checking.
*
* Override this if storage has more efficient way of checking for updates.
*
* @abstract
*/
async updateCheckImpl()
{
if (!this.bruteForceNotified)
{
console.log('WARNING: UPDATE IS NOT NATIVELY SUPPORTED BY STORAGE; USING BRUTE FORCE UPDATE. THIS MAY BE SLOWER AND LEAD TO GREATER BANDWIDTH USAGE.');
/**
* if there are no efficient way of checking update, make a warning notification once
*/
this.bruteForceNotified = true;
}
let updated = false;
let records = await this.readAllRecords();
let newlist = {},
type, record = {},
list = this.lookup;
for (let record of records)
{
newlist[record[this.primaryKey]] = record;
}
if (!list)
{
this.lookup = newlist;
return false;
}
// check for deleted item
type = 'delete';
for (let item in list)
{
if (!newlist[item])
{
record[this.primaryKey] = item;
this.emit(type, record);
delete list[record[this.primaryKey]];
updated = true;
}
}
// check for new items
type = 'create';
for (let item in newlist)
{
if (!list[item])
{
record = newlist[item];
this.emit(type, record);
updated = true;
list[record[this.primaryKey]] = record;
}
}
// check for modified items
type = 'update';
for (let item in list)
{
if (JSON.stringify(list[item]) !== JSON.stringify(newlist[item]))
{
record = newlist[item];
this.emit(type, record);
updated = true;
list[record[this.primaryKey]] = record;
}
}
return updated;
}
/**
* Stop checking for updates.
* Required for use with CachedCollection
*/
stopRecordUpdateCheck()
{
if (this.timeout)
{
clearTimeout(this.timeout);
this.timeout = undefined;
}
}
}
module.exports = Storage;
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