export class RunOnceScheduler {

	private timeoutToken: any;
	private runner: () => void;
	private timeout: number;
	private timeoutHandler: () => void;

	constructor(runner: () => void, timeout: number) {
		this.timeoutToken = -1;
		this.runner = runner;
		this.timeout = timeout;
		this.timeoutHandler = this.onTimeout.bind(this);
	}

	/**
	 * Dispose RunOnceScheduler
	 */
	dispose(): void {
		this.cancel();
		this.runner = null;
	}

	/**
	 * Cancel current scheduled runner (if any).
	 */
	cancel(): void {
		if (this.isScheduled()) {
			clearTimeout(this.timeoutToken);
			this.timeoutToken = -1;
		}
	}

	/**
	 * Replace runner. If there is a runner already scheduled, the new runner will be called.
	 */
	setRunner(runner: () => void): void {
		this.runner = runner;
	}

	/**
	 * Cancel previous runner (if any) & schedule a new runner.
	 */
	schedule(delay = this.timeout): void {
		this.cancel();
		this.timeoutToken = setTimeout(this.timeoutHandler, this.timeout);
	}

	/**
	 * Returns true if scheduled.
	 */
	isScheduled(): boolean {
		return this.timeoutToken !== -1;
	}

	private onTimeout() {
		this.timeoutToken = -1;
		if (this.runner) {
			this.runner();
		}
	}
}