/**
 * 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 result = await getData(itemsSelector, fieldSelectors, ...args);
    if (confirm(
            `Click confirm to download if the sample data looks good (${result.data.length} items)：\n\n${result.toString(50) || "- Empty -"}`
        )) {
        saveFile(result, "text/csv");
    }
}

/**
 * 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) {
    if (!testArgs(itemsSelector, fieldSelectors, ...args))
        throw new Error(`Invalid call arguments.\n\n${signitures}\n\n`);
    let urls = [];
    if (args.length) {
        let arg = args.shift();
        if (arg instanceof Array) {
            urls = arg;
        } else if (arg instanceof ExtractResult) {
            urls = arg.squash().filter(v => !!v);
        } else {
            let urlTempl = arg;
            if (urlTempl) {
                if (args[0] instanceof Array) {
                    urls = args[0].map(p => urlTempl.replace("${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 = [];
    let tab = await getActiveTab(true) || await getActiveTab(false);
    if (!tab) throw new Error("Cannot find active tab.");
    return new Promise((resolve, reject) => {
        let pms;
        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(new ExtractResult(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 && r.length;
    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} interval interval for detecting
 * @return {Promise} a promise of the response.
 */
function sendMessage(tab, req, cond, interval) {
    req.from = "DataExtracter:" + req.from;
    interval = interval || 500;
    return new Promise((resolve, reject) => {

        loop();

        async function loop() {
            console.log("request for", req.from);
            let tabAvailable = await getTabByID(tab.id);
            if (!tabAvailable) {
                reject("Task interrupted due to the target tab is closed.");
                return;
            }

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

async function getActiveTab(currentWindow) {
    return new Promise((resolve, reject) => {
        chrome.tabs.query({
            active: true,
            currentWindow: currentWindow
        }, function (tabs) {
            resolve(tabs[0]);
        })
    })
}

async function getTabByID(id) {
    return new Promise((resolve, reject) => {
        chrome.tabs.get(id, function (tab) {
            chrome.runtime.lastError;
            resolve(tab);
        })
    })
}