class Tracker {
  _servers = [];

  /**
   *
   * @param {string} hostType 
   * @example
   *   allocate("south")
   */
  allocate(hostType) {
    const nextAvailableServer = this._nextAvailableServer(this._servers);
    this._servers.push(nextAvailableServer);
    return `${hostType}${nextAvailableServer}`;
  }

  /**
   *
   * @param {string} hostName 
   * @example
   *   deallocate("south3")
   */
  deallocate(hostName) {
    console.log(`Removing ${hostName} from servers...`);
    const numberMatch = hostName.match(/\d+/)[0];
    const serverNumber = Number(numberMatch);

    const updatedServers = this._servers.filter((s) => s !== serverNumber);
    console.log(`Servers after removal of ${hostName}: ${updatedServers}`);
    this._servers = updatedServers;
  }

  /**
   *
   * @param {Array} servers
   * @example
   *   _nextAvailableServer([5,3,1])
   * @returns number
   */
  _nextAvailableServer(servers) {
    if (!servers.length) {
      return 1;
    }

    // Operate on sorted servers to assure loop always runs the same
    const sortedServers = servers.sort();

    let lowestAvailable;
    let counter = 1;

    sortedServers.forEach((server) => {
      if (server !== counter) {
        lowestAvailable = counter;
        return;
      }

      // This keeps track of the incremental server numbers
      counter++;
    });

    return lowestAvailable || counter; // If there are no available in range of server array, just return counter (next)
  }
}

const tracker = new Tracker();

const test1 = tracker._nextAvailableServer([5, 3, 1]);
const test2 = tracker._nextAvailableServer([3, 2, 1]);

console.log("servers at start:", tracker._servers);

tracker.allocate("south");
tracker.allocate("south");
tracker.allocate("south");

console.log(tracker.allocate("south"));
console.log(tracker.allocate("south"));
console.log(tracker.allocate("south"));
console.log(tracker.allocate("south"));
console.log(tracker.deallocate("south5"));

console.log(tracker._servers);