/**
* Copyright 2025 Chris Bunting <cbuntingde@gmail.com>
*
* Rate Limiter - Token bucket algorithm for API rate limiting
*/
import { config } from './config.js';
import { RateLimitError } from './errors.js';
import { logger } from './logger.js';
interface TokenBucket {
tokens: number;
lastRefill: number;
capacity: number;
refillRate: number; // tokens per millisecond
}
class RateLimiter {
private buckets: Map<string, TokenBucket> = new Map();
private readonly capacity: number;
private readonly refillRate: number;
constructor(capacity: number, tokensPerHour: number) {
this.capacity = capacity;
// Convert tokens per hour to tokens per millisecond
this.refillRate = tokensPerHour / (60 * 60 * 1000);
}
/**
* Try to consume a token from the bucket
* @returns true if token was consumed, false if rate limit exceeded
*/
tryConsume(key: string = 'default'): boolean {
const now = Date.now();
let bucket = this.buckets.get(key);
if (!bucket) {
bucket = {
tokens: this.capacity,
lastRefill: now,
capacity: this.capacity,
refillRate: this.refillRate,
};
this.buckets.set(key, bucket);
}
// Refill tokens based on time elapsed
const timeElapsed = now - bucket.lastRefill;
const tokensToAdd = timeElapsed * bucket.refillRate;
bucket.tokens = Math.min(bucket.capacity, bucket.tokens + tokensToAdd);
bucket.lastRefill = now;
// Try to consume a token
if (bucket.tokens >= 1) {
bucket.tokens -= 1;
return true;
}
return false;
}
/**
* Wait until a token is available
*/
async waitForToken(key: string = 'default', maxWait: number = 60000): Promise<void> {
const startTime = Date.now();
while (!this.tryConsume(key)) {
const elapsed = Date.now() - startTime;
if (elapsed >= maxWait) {
throw new RateLimitError('Rate limit exceeded: maximum wait time reached', undefined, { key, maxWait });
}
// Wait before retrying (exponential backoff)
const waitTime = Math.min(1000 * Math.pow(2, Math.floor(elapsed / 5000)), 5000);
await new Promise(resolve => setTimeout(resolve, waitTime));
}
}
/**
* Get remaining tokens
*/
getRemainingTokens(key: string = 'default'): number {
const bucket = this.buckets.get(key);
if (!bucket) {
return this.capacity;
}
const now = Date.now();
const timeElapsed = now - bucket.lastRefill;
const tokensToAdd = timeElapsed * bucket.refillRate;
const currentTokens = Math.min(bucket.capacity, bucket.tokens + tokensToAdd);
return Math.max(0, Math.floor(currentTokens));
}
/**
* Reset bucket for a key
*/
reset(key: string = 'default'): void {
this.buckets.delete(key);
}
}
export const rateLimiter = new RateLimiter(
config.GITHUB_RATE_LIMIT_BURST,
config.GITHUB_RATE_LIMIT_PER_HOUR
);
