data-extracter-extesion/src/background/messaging.ts

import { Request, Actions, Response } from "../common";
import { getTabByID } from "./actions";
import { logger } from "../common/logger";


export type ResponseCheckerSync<T> = (r: Response<T>, err: chrome.runtime.LastError, count: number) => T;
export type ResponseCheckerAsync<T> = (r: Response<T>, err: chrome.runtime.LastError, count: number) => Promise<T>;
export type ResponseChecker<T> = ResponseCheckerSync<T> | ResponseCheckerAsync<T>;
/**
 *  Sending a message to target tab repeatedly until the response is not undefined.
 * @param {object} tab the table where to send the message
 * @param {object} req the request data.
 * @param {function} dataChecker (reulst:any, err:error, tryCount:number) => any. 
 * Check and decide what value finally returns. 
 * Return undefined to make 'sendMessage' retry. 
 * Return MSG_USER_ABORT to cancel this promise.
 * @param {number} interval retry interval, default: 500ms.
 * @param {number} limit retry limit, default: 0, no limit.
 * @param {string} log messages logged to console.
 * @return {Promise} a promise of the response.
 */
export function sendMessage<T>(
    tab: chrome.tabs.Tab,
    req: Request,
    log?: string,
    dataChecker?: ResponseChecker<T>,
    timeout?: number,
    interval?: number,
    limit?: number
) {
    timeout = timeout || 10;
    interval = interval || 500;
    limit = isNaN(limit) ? 0 : limit;
    let count = 0;
    return new Promise<T>((resolve, reject) => {

        loop();

        async function loop() {
            logger.debug("Request for", Actions[req.action]);
            let tabAvailable = await getTabByID(tab.id);
            if (!tabAvailable) {
                reject("Task interrupted due to the target tab is closed.");
                return;
            }

            if (limit && count >= limit) {
                reject(`sendMessage loop limit ${limit} reached.`);
                return;
            }
            count++;
            let timeout = setTimeout(() => { reject(`${Actions[req.action]} requset timeout after ${timeout}s`) }, 10000);
            chrome.tabs.sendMessage(tab.id, req, async (r: Response<T>) => {
                clearTimeout(timeout);
                // check error but do nothing until dataChecker.
                let err = chrome.runtime.lastError;
                let [result, error] = await checkResponse(dataChecker, r, err, count);
                if (error) {
                    reject(error);
                    return;
                }
                let flag = result !== undefined;
                if (log) logger.info(log, flag ? '(OK)' : '(failed)');
                if (flag) {
                    resolve(result);
                } else {
                    setTimeout(() => {
                        logger.debug('Invalid response', r, 'retry...');
                        loop();
                    }, interval);
                }
            });
        }
    });
}

async function checkResponse<T>(
    dataChecker: ResponseChecker<T>,
    response: Response<T>,
    error: chrome.runtime.LastError,
    tryCount: number
): Promise<[T, string]> {
    // response could be undefined if the content script is interrupted.
    // don't check, tell sendMessage to retry.
    if (!response) return [undefined, undefined];
    if (!dataChecker) {
        return [response.result, response.error];
    }
    let result: T;
    let pms: T | Promise<T>;
    try {
        pms = dataChecker(response, error, tryCount);
    } catch (err) {
        return [undefined, err];
    }
    // don't catch if it's not a Promise
    if (pms instanceof Promise) {
        let checkerError: any;
        pms = pms.catch(e => checkerError = e);
        result = await pms;
        if (checkerError) {
            return [undefined, checkerError];
        }
    } else {
        result = pms;
    }
    return [result, undefined];
}

export type ActionSubscriberSync = (request: Request, sender: chrome.runtime.MessageSender, sendResponse: (response?: any) => void) => void;
export type ActionSubscriberAsync = (request: Request, sender: chrome.runtime.MessageSender, sendResponse: (response?: any) => void) => Promise<void>;
export type ActionSubscriber = ActionSubscriberSync | ActionSubscriberAsync;

class MessageSubscribers {
    private listeners: { [key: number]: ActionSubscriber[] } = {};
    addListener(action: Actions, subscriber: ActionSubscriber) {
        this.listeners[action] || (this.listeners[action] = []);
        this.listeners[action].push(subscriber);
    }
    removeListener(action: Actions, subscriber: ActionSubscriber) {
        this.listeners[action] || (this.listeners[action] = []);
        for (let i = 0; i < this.listeners[action].length; i++) {
            if (this.listeners[action][i] == subscriber) {
                this.listeners[action].splice(i, 1);
                i--;
            }
        }
        logger.debug(`${this.listeners[action].length} subscriber(s) remained for action ${Actions[action]}`);
    }
    getListeners(action: Actions): ActionSubscriber[] {
        return this.listeners[action]
    }
}
export const messageSubscribers = new MessageSubscribers();

chrome.runtime.onMessage.addListener(function (request: Request, sender, sendResponse) {
    let subscribers = messageSubscribers.getListeners(request.action);
    if (!subscribers || !subscribers.length) {
        sendResponse("Request not supported.");
        return;
    }
    let promises: Promise<any>[] = [];
    for (let subscriber of subscribers) {
        let p = subscriber(request, sender, sendResponse);
        if (p instanceof Promise) promises.push(p);
    }
    if (promises.length)
        return Promise.all(promises);
    return;
});