[EmperioAf]

const queue = require('async').queue;
const request = require('request');

/** Class control free keys. */
function ApiKeys(apiKeys) {
    this.apiKeys = apiKeys;
    this.locked = {};
}

/**
 * Get a free key and lock it
 * @return {string} Key.
 */
ApiKeys.prototype.getKey = function () {
    for (const key of this.apiKeys) {
        if (!this.locked[key]) {
            this.locked[key] = true;
            return key;
        }
    }
}

/**
 * Method free key for next request
 * @param {string} key - Locked key.
 */
ApiKeys.prototype.freeKey = function (key) {
    this.locked[key] = false;
}

const API_KEYS = ['key1', 'key2', 'key3', 'key4', 'key5', 'key6', 'ke7', 'key8'];
const MAX_WORKERS_IN_QUEUE = API_KEYS.length;

const apiKeys = new ApiKeys(API_KEYS);


const requestQueue = queue(function (task, callback) {
    const key = apiKeys.getKey();
    task.options.url += '&key=' + key;
    request(task.options, (err, res, body) => {
        apiKeys.freeKey(key);
        callback(err, res, body);
    })
}, MAX_WORKERS_IN_QUEUE);


const requestUrls = [];
for (const url of requestUrls) {
    const options = {
        url: url,
        method: 'GET'
    };
    requestQueue.push({ options: options }, function (err, res, body) {
        // process response here
    });
}
requestQueue.drain = function () {
    console.log('all items have been processed');
};