/**
 * Extract data from current page / multiple urls.
 * getData(tab, itemsSelector:string, fieldSelectors:string[])
 * getData(tab, itemsSelector:string, fieldSelectors:string[], url:string, from:number, to:number, interval:number)
 * getData(tab, itemsSelector:string, fieldSelectors:string, url:string, pages:number[])
 * getData(tab, itemsSelector:string, fieldSelectors:string[], urls:string[])
 * getData(tab, itemsSelector:string, fieldSelectors:string[], urls:ExtractResult)
 * getData(itemsSelector:string, fieldSelectors:string[])
 * getData(itemsSelector:string, fieldSelectors:string[], url:string, from:number, to:number, interval:number)
 * getData(itemsSelector:string, fieldSelectors:string, url:string, pages:number[])
 * getData(itemsSelector:string, fieldSelectors:string[], urls:string[])
 * getData(itemsSelector:string, fieldSelectors:string[], urls:ExtractResult)
 * @param {...any} args
 */
async function getData(...args) {
    let tab;
    if (typeof args[0] !== 'string') tab = args.shift();
    if (!testArgs(...args))
        throw new Error(`Invalid call arguments.\n\n${signitures}\n\n`);
    itemsSelector = args.shift();
    fieldSelectors = args.shift();
    let urls = parseUrls(...args);
    let data = [];
    if (!tab) 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 => {
                    if (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 => {
                if (results) data.push(...results);
                data.unshift(fieldSelectors);
                resolve(new ExtractResult(data));
            },
            err => reject(err)
        );
    });
}

function parseUrls(...args) {
    if (!args.length) return [];
    let arg = args.shift();
    if (arg instanceof Array) {
        return arg;
    } else if (arg instanceof ExtractResult) {
        return arg.squash().filter(v => URL_REG.test(v));
    } else {
        let urlTempl = arg;
        if (urlTempl) {
            if (args[0] instanceof Array) {
                return args[0].map(p => urlTempl.replace("${page}", p));
            } else if (args.length >= 3) {
                let urls = [];
                let from = args.shift();
                let to = args.shift();
                let interval = args.shift();
                for (let i = from; i <= to; i += interval) {
                    urls.push(urlTempl.replace("${page}", i));
                }
                return urls;
            }
        }
    }
    return [];
}

function redirectTab(tab, url) {
    let curUrl = "";
    return queryUrl(tab, undefined, 'Query current url...')
        .then(u => {
            if (url !== u) {
                curUrl = u;
                let req = {
                    action: ACTION_GOTO_URL,
                    url: url
                }
                return sendMessage(tab, req, `Goto url: ${url}`);
            }
        })
        .then(() => queryUrl(tab, url, 'Check if tab url matches expected...'))
}

/**
 * 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 = {
        action: ACTION_EXTRACT,
        itemsSelector: itemsSelector,
        fieldSelectors: fieldSelectors
    }
    let cond = r => !MSG_ELEMENT_NOT_FOUND.isEqual(r);
    return sendMessage(tab, req, 'Extract data from the tab...', 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 = {
        action: ACTION_REPORT_IN
    }
    let cond = r => r == req.action;
    return sendMessage(tab, req, 'Check tab availability...', cond);
}

/**
 * get the url of the target tab
 * @param {any} tab target tab
 * @param {string} expected if specified, queryUrl resolves only when tab url equals to expected
 * @returns {Promise<string>} a promise of the url
 */
function queryUrl(tab, expected, log) {
    let req = {
        action: ACTION_QUERY_URL
    }
    let cond = url => url && (!expected || (expected && expected == url));
    return sendMessage(tab, req, log, cond);
}

/**
 * get the url of the target tab
 * @param {any} tab target tab
 * @param {string} expected if specified, queryUrl resolves only when tab url equals to expected
 * @returns {Promise<string>} a promise of the url
 */
function scrollToBottom(tab) {
    let req = {
        action: ACTION_SCROLL_BOTTOM
    }
    return sendMessage(tab, req, 'Scroll to page bottom...');
}

async function createTab(url, active) {
    return new Promise((resolve, reject) => {
        chrome.tabs.create({
            'url': url,
            'active': active
        }, function (tab) {
            resolve(tab);
        })
    })
}

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);
        })
    })
}