import {Express, Router} from "express";
import Logger from "./Logger";
import {sleep} from "./Utils";

export default abstract class ApplicationComponent<T> {
    private val?: T;

    public abstract async start(app: Express, router: Router): Promise<void>;

    public abstract async stop(): Promise<void>;

    protected export(val: T) {
        this.val = val;
    }

    public import(): T {
        if (!this.val) throw 'Cannot import if nothing was exported.';
        return this.val;
    }

    protected async prepare(name: string, prepare: () => Promise<void>): Promise<void> {
        let err;
        do {
            try {
                await prepare();
                err = null;
            } catch (e) {
                err = e;
                Logger.error(err, `${name} failed to prepare; retrying in 5s...`)
                await sleep(5000);
            }
        } while (err);
        Logger.info(`${name} ready!`);
    }

    protected async close(thingName: string, thing: any, fn: Function): Promise<void> {
        try {
            await new Promise((resolve, reject) => fn.call(thing, (err: any) => {
                if (err) reject(err);
                else resolve();
            }));

            Logger.info(`${thingName} closed.`);
        } catch (e) {
            Logger.error(e, `An error occurred while closing the ${thingName}.`);
        }
    }
}