/**
 * Port allocator for virtual host tunnel local ports.
 * Each virtual host gets a unique port on 127.0.0.1 starting at TUNNEL_PORT_BASE.
 * Released ports are recycled via a free list.
 */

const TUNNEL_PORT_BASE = 19000;

let nextTunnelPortIndex = 0;
const tunnelPortFreeList = [];

/**
 * Allocate a unique local port for a virtual host tunnel.
 * Recycles ports from the free list before incrementing the counter.
 * @returns {number} An available port number >= TUNNEL_PORT_BASE.
 */
function allocateTunnelPort() {
  if (tunnelPortFreeList.length > 0) return tunnelPortFreeList.pop();
  return TUNNEL_PORT_BASE + (nextTunnelPortIndex++);
}

/**
 * Return a port to the free list so it can be reused by a future allocation.
 * Silently ignores invalid ports and duplicate releases.
 * @param {number} port - The port to release. Must be >= TUNNEL_PORT_BASE.
 */
function releaseTunnelPort(port) {
  if (typeof port === 'number' && port >= TUNNEL_PORT_BASE && !tunnelPortFreeList.includes(port)) {
    tunnelPortFreeList.push(port);
  }
}

module.exports = { TUNNEL_PORT_BASE, allocateTunnelPort, releaseTunnelPort };