class Task {
    _data = {};
    _data_keys = [];
    /**
     * Create a task.
     * constructor(itemsSelector:string, fieldSelectors:string[])
     * constructor(itemsSelector:string, fieldSelectors:string[], url:string, from:number, to:number, interval:number)
     * constructor(itemsSelector:string, fieldSelectors:string[], url:string, pages:number[])
     * constructor(itemsSelector:string, fieldSelectors:string[], urls:string[])
     * @param {...any} args
     */
    constructor(options, ...args) {
        if (!testArgs(...args))
            throw new Error(`Invalid call arguments.\n\n${signitures}\n\n`);
        this._options = options;
        this._itemsSelector = args.shift();
        this._fieldSelectors = args.shift();
        this._urls = parseUrls(...args);
    }
    get urls() {
        return this._urls;
    }
    get data() {
        return this._data;
    }
    get results() {
        return this._data_keys.reduce((p, c) => {
            return p.concat(this._data[c]);
        }, []);
    }
    get fieldSelectors() {
        return this._fieldSelectors;
    }
    clean() {
        this._data = {};
    }
    async execute(tab, upstreamData) {
        if (!tab) return Promise.reject("No tab to execute the task.");
        let urls = this._urls
        if (!urls.length) {
            if (upstreamData) {
                urls = parseUrls(upstreamData);
            } else {
                urls = [await queryUrl(tab)];
            }
        }
        let saveResult = (results, key) => {
            this._data[key] = results;
            this._data_keys.push(key);
        }
        return urls.reduce((p, url, i) => p.then(
            results => {
                if (i > 0) {
                    if (!MSG_URL_SKIPPED.isEqual(results)) {
                        let lastURL = urls[i - 1];
                        saveResult(results, lastURL);
                    }
                }
                if (this._data[url]) return MSG_URL_SKIPPED;
                let pms = redirectTab(tab, url);
                if (this._options["scrollToBottom"]) {
                    pms = pms.then(() => scrollToBottom(tab));
                }
                return pms.then(
                    () => extractTabData(tab, this._itemsSelector, this._fieldSelectors)
                );
            }
        ), Promise.resolve(null)).then(
            results => {
                if (!MSG_URL_SKIPPED.isEqual(results)) {
                    let lastURL = urls[urls.length - 1];
                    saveResult(results, lastURL);
                    return;
                }
            }
        );
    }
}