'use strict';
const DEFAULT_LIMIT = 25;
const DEFAULT_INCREMENT_INTERVAL = 5000;
const DEFAULT_INCREMENT = 1;
/**
* TokenBucket
*
* Handles how many tokens are available at any given time based on
* the configuration set and the token bucket algorithm.
*
* @see https://en.wikipedia.org/wiki/Token_bucket
*/
class TokenBucket {
/**
* Creates a TokenBucket object.
*
* @param {object} config configuration values
* @param {integer} [config.limit=25] The max amount of tokens per incrementInterval.
* @param {integer} [config.incrementInterval=5000] The time in ms before tokens will increment.
* @param {integer} [config.increment=1] The amount of tokens that will increment each incrementInterval.
*/
constructor(config) {
config = config || {};
const incrementInterval = config.incrementInterval || DEFAULT_INCREMENT_INTERVAL;
this.limit = this.tokens = config.limit || DEFAULT_LIMIT;
this.increment = config.increment || DEFAULT_INCREMENT;
this._interval = setInterval(() => {
this._incrementTokens();
}, incrementInterval);
}
/**
* Cleans up the interval set by the constructor.
*/
destroy() {
clearInterval(this._interval);
this._interval = null;
}
/**
* Helper to increment tokens on the interval.
*
* @private
*/
_incrementTokens() {
if (this.tokens < this.limit) {
this.tokens += this.increment;
if (this.tokens > this.limit) {
this.tokens = this.limit;
}
}
}
/**
* Decrements the amount of tokens available based on amount
* and returns the value.
*
* @param {integer} [amount=1] The number to decrement by
* @return {integer} The remaining available requests for the identifier
*/
decrementTokens(amount) {
amount = amount || 1;
if (this.tokens >= amount) {
this.tokens -= amount;
}
else {
throw new Error('not enough tokens');
}
return this.tokens;
}
/**
* Returns the currently available tokens.
*
* @return {integer} The remaining available requests for the identifier
*/
getTokensRemaining() {
return this.tokens;
}
};
module.exports = TokenBucket;
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