/**
 * 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
 * @param {string} log messages logged to console.
 * @return {Promise} a promise of the response.
 */
function sendMessage(tab, req, log, cond, interval) {
    interval = interval || 500;
    return new Promise((resolve, reject) => {

        loop();

        async function loop() {
            // console.log("request for", req.action);
            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 => {
                // check error but do nothing.
                // do not interrupt promise chains even if error, or the task always fail when:
                // a tab is newly created, and the content scripts won't have time to initialize
                chrome.runtime.lastError;

                let flag = !cond || cond(r);
                if (log) console.log(log, flag ? '(OK)' : '(failed)');
                if (flag) {
                    resolve(r);
                } else {
                    setTimeout(() => {
                        loop();
                    }, interval);
                }
            });
        }
    });
}

chrome.runtime.onMessage.addListener(function (message, sender, sendResponse) {
    if (!message.action || !message.action.startsWith(EXT_NAME)) {
        return;
    }
    sendResponse("Calling from user pages is not allowed.");
    return;
});