class SimpleSchedule {

    private task_is_running: boolean;
    private taskCaller: () => Promise<any>;
    private trackInterval: NodeJS.Timeout | null;
    private checkInterval: number; //default

    constructor(taskFn: () => Promise<any>, checkInterval: number = 5) {
        this.taskCaller = taskFn;
        this.task_is_running = false;
        this.trackInterval = null;
        this.checkInterval = checkInterval;
    }

    start = () => {
        console.log(`Schedule ${this.taskCaller.name} started at ${this.timeNow()}`);

        this.trackInterval = setInterval(async () => {
            // flag for long-running task so another instance wont start
            if(this.task_is_running) {
                console.log(`Task ${this.taskCaller.name} is still running. Check time ${this.timeNow()}`);
                return;
            }

            this.task_is_running = true;
            console.log(`OK invoke ${this.taskCaller.name} at ${this.timeNow()}`);
            await this.taskCaller();
            this.task_is_running = false;
        }, this.checkInterval * 1000 );
    }

    getInterval = (): number => this.checkInterval;

    changeInterval = (new_interval: number) => {
        if(new_interval === this.checkInterval) {
            return; // nothing change!
        }

        // remove running
        if(this.trackInterval) clearInterval(this.trackInterval);

        // set and start
        this.checkInterval = new_interval;
        this.start();
    }

    stop = () => {
        console.log(`Schedule ${this.taskCaller.name} stoped at ${this.timeNow()}`);
        if(this.trackInterval) clearInterval(this.trackInterval);
    }

    timeNow = () => {
        return Math.floor(Date.now() / 1000);
    }
}

export default SimpleSchedule;