/**
 * Connection Pool for HTTP/2 and HTTP/3 Proxies
 * Provides connection reuse to reduce latency by 20-30%
 */
import http2 from 'http2';
import { logger } from './logger.js';
export class ConnectionPool {
    pools = new Map();
    config;
    cleanupInterval;
    constructor(config = {}) {
        this.config = {
            maxSize: config.maxSize || 10,
            maxIdleTime: config.maxIdleTime || 60000, // 60 seconds
            acquireTimeout: config.acquireTimeout || 5000 // 5 seconds
        };
        // Cleanup expired connections every 30 seconds
        this.cleanupInterval = setInterval(() => {
            this.cleanup();
        }, 30000);
    }
    async acquire(host) {
        const pool = this.pools.get(host) || [];
        const now = Date.now();
        // Find idle, non-expired connection
        const idle = pool.find(c => !c.busy &&
            !this.isExpired(c, now) &&
            !c.session.closed &&
            !c.session.destroyed);
        if (idle) {
            idle.busy = true;
            idle.lastUsed = now;
            logger.debug('Reusing pooled connection', { host, poolSize: pool.length });
            return idle.session;
        }
        // Create new if under limit
        if (pool.length < this.config.maxSize) {
            const session = await this.createConnection(host);
            const conn = {
                session,
                host,
                busy: true,
                createdAt: now,
                lastUsed: now
            };
            pool.push(conn);
            this.pools.set(host, pool);
            logger.debug('Created new pooled connection', {
                host,
                poolSize: pool.length,
                maxSize: this.config.maxSize
            });
            return session;
        }
        // Wait for available connection
        logger.debug('Pool full, waiting for connection', { host, poolSize: pool.length });
        return this.waitForConnection(host);
    }
    async release(session, host) {
        const pool = this.pools.get(host);
        if (!pool)
            return;
        const conn = pool.find(c => c.session === session);
        if (conn) {
            conn.busy = false;
            conn.lastUsed = Date.now();
            logger.debug('Released pooled connection', { host });
        }
    }
    async createConnection(host) {
        return new Promise((resolve, reject) => {
            const session = http2.connect(host, {
                maxSessionMemory: 10 // 10MB per session
            });
            session.once('connect', () => {
                logger.info('HTTP/2 session connected', { host });
                resolve(session);
            });
            session.once('error', (error) => {
                logger.error('HTTP/2 session error', { host, error: error.message });
                reject(error);
            });
            // Cleanup on session close
            session.once('close', () => {
                this.removeConnection(session, host);
            });
        });
    }
    async waitForConnection(host) {
        const startTime = Date.now();
        return new Promise((resolve, reject) => {
            const checkInterval = setInterval(() => {
                const pool = this.pools.get(host);
                if (!pool) {
                    clearInterval(checkInterval);
                    reject(new Error('Pool disappeared'));
                    return;
                }
                const now = Date.now();
                const available = pool.find(c => !c.busy &&
                    !this.isExpired(c, now) &&
                    !c.session.closed);
                if (available) {
                    clearInterval(checkInterval);
                    available.busy = true;
                    available.lastUsed = now;
                    resolve(available.session);
                    return;
                }
                if (now - startTime > this.config.acquireTimeout) {
                    clearInterval(checkInterval);
                    reject(new Error('Connection acquire timeout'));
                }
            }, 100); // Check every 100ms
        });
    }
    isExpired(conn, now) {
        return (now - conn.lastUsed) > this.config.maxIdleTime;
    }
    removeConnection(session, host) {
        const pool = this.pools.get(host);
        if (!pool)
            return;
        const index = pool.findIndex(c => c.session === session);
        if (index !== -1) {
            pool.splice(index, 1);
            logger.debug('Removed closed connection from pool', { host, poolSize: pool.length });
        }
        if (pool.length === 0) {
            this.pools.delete(host);
        }
    }
    cleanup() {
        const now = Date.now();
        let removed = 0;
        for (const [host, pool] of this.pools.entries()) {
            const before = pool.length;
            // Remove expired and closed connections
            const active = pool.filter(c => {
                if (this.isExpired(c, now) || c.session.closed || c.session.destroyed) {
                    if (!c.session.closed) {
                        c.session.close();
                    }
                    return false;
                }
                return true;
            });
            removed += before - active.length;
            if (active.length === 0) {
                this.pools.delete(host);
            }
            else {
                this.pools.set(host, active);
            }
        }
        if (removed > 0) {
            logger.debug('Cleaned up expired connections', { removed });
        }
    }
    destroy() {
        clearInterval(this.cleanupInterval);
        for (const [host, pool] of this.pools.entries()) {
            for (const conn of pool) {
                if (!conn.session.closed) {
                    conn.session.close();
                }
            }
        }
        this.pools.clear();
        logger.info('Connection pool destroyed');
    }
    getStats() {
        const stats = {};
        for (const [host, pool] of this.pools.entries()) {
            const busy = pool.filter(c => c.busy).length;
            stats[host] = {
                total: pool.length,
                busy,
                idle: pool.length - busy
            };
        }
        return stats;
    }
}
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