/**
 * Extract data from current tab / multiple urls.
 * @param {string} itemsSelector items selectors for selecting items (data rows)
 * @param {Array<string>} fieldSelectors fields selectors for selecting fields (data columns) under each item
 * @param {...any} args url list / url templates, page numers, either [from, to, interval] or [...pages]
 */
async function extract(itemsSelector, fieldSelectors, ...args) {
    let data = await getData(itemsSelector, fieldSelectors, ...args);
    data.unshift(fieldSelectors);
    saveFileAsk(data);
}

/**
 * Extract data from current tab / multiple urls.
 * @param {string} itemsSelector items selectors for selecting items (data rows)
 * @param {Array<string>} fieldSelectors fields selectors for selecting fields (data columns) under each item
 * @param {...any} args url list / url templates, page numers, either [from, to, interval] or [...pages]
 */
async function getData(itemsSelector, fieldSelectors, ...args) {
    let urls = [];
    let arg = args.shift();
    if (arg instanceof Array) {
        urls = arg;
    } else {
        let urlTempl = arg;
        if (urlTempl) {
            if (args[0] instanceof Array) {
                urls = args[0].map(p => urlTempl.replace("${page}", p));
            } else if (args.length >= 3) {
                let from = args.shift();
                let to = args.shift();
                let interval = args.shift();
                for (let i = from; i <= to; i += interval) {
                    urls.push(urlTempl.replace("${page}", i));
                }
            }
        }
    }
    let data = [];
    return new Promise((resolve, reject) => {
        chrome.tabs.query({
            active: true,
            currentWindow: false
        }, function (tabs) {
            let pms;
            let tab = tabs[0];
            if (urls.length) {
                pms = urls.reduce((p, url) => p.then(
                    results => {
                        data.push(...results);
                        return redirectTab(tab, url).then(
                            () => extractTabData(tab, itemsSelector, fieldSelectors)
                        );
                    },
                    () => p
                ), Promise.resolve([]));
            } else {
                pms = extractTabData(tab, itemsSelector, fieldSelectors);
            }
            pms.then(
                results => {
                    data.push(...results);
                    resolve(data);
                },
                err => reject(err)
            );
        });
    });
}

function redirectTab(tab, url) {
    let curUrl = "";
    return queryUrl(tab)
        .then(u => {
            if (url !== u) {
                curUrl = u;
                let req = {
                    from: "GotoUrl",
                    url: url
                }
                sendMessage(tab, req);
            }
        })
        .then(() => queryUrl(tab, curUrl))
        .then(() => reportIn(tab));
}

/**
 * extract data in from the target tab.
 * @param {any} tab target tab
 * @param {string} itemsSelector items selectors for selecting items (data rows)
 * @param {Array<string>} fieldSelectors fields selectors for selecting fields (data columns) under each item
 * @returns {Promise<string[]>} a promise of extracted data
 */
function extractTabData(tab, itemsSelector, fieldSelectors) {
    let req = {
        from: "Extract",
        itemsSelector: itemsSelector,
        fieldSelectors: fieldSelectors
    }
    let cond = r => !!r;
    return sendMessage(tab, req, cond);
}

/**
 * get report in from the target tab, usually used to detect if the content script is ready.
 * @param {any} tab target tab
 * @returns {Promise<string>} a promise of the report in message
 */
function reportIn(tab) {
    let req = {
        from: "ReportIn"
    }
    let cond = r => r == req.from;
    return sendMessage(tab, req, cond);
}

/**
 * get the url of the target tab
 * @param {any} tab target tab
 * @param {string} urlExcluded if specified, queryUrl resolves only when response not equals to urlExcluded
 * @returns {Promise<string>} a promise of the url
 */
function queryUrl(tab, urlExcluded) {
    let req = {
        from: "QueryUrl"
    }
    let cond = url => url && (!urlExcluded || (urlExcluded && urlExcluded != url));
    return sendMessage(tab, req, cond);
}

/**
 * Repeatedly sending a message to target tab until the response is detected good.
 * @param {object} tab the table where to send the message
 * @param {object} req the request data.
 * @param {function} cond success condition function, r:any=>boolean
 * @param {number} failedTimeOut fail time out
 * @param {number} detectInterval interval for detecting
 * @return {Promise} a promise of the response.
 */
function sendMessage(tab, req, cond, failedTimeOut, detectInterval) {
    req.from = "DataExtracter:" + req.from;
    failedTimeOut = failedTimeOut || 10000;
    detectInterval = detectInterval || 500;
    return new Promise((resolve, reject) => {
        let timeOut;
        let rejectTimeout = setTimeout(() => {
            reject(`${req.from} failed after ${failedTimeOut/1000} seconds.`);
            clearTimeout(timeOut);
        }, failedTimeOut);
        loop();

        function loop() {
            chrome.tabs.sendMessage(tab.id, req, r => {
                if (!cond || cond(r)) {
                    clearTimeout(rejectTimeout);
                    resolve(r);
                } else {
                    timeOut = setTimeout(() => {
                        loop();
                    }, detectInterval);
                }
            });
        }
    });
}