import type { ImportState } from "$lib/api/repo";

interface ImportPollOptions {
	fetchState: () => Promise<ImportState | null>;
	onState: (state: ImportState | null) => void;
	onSettled?: () => void;
	minDelayMs?: number;
	maxDelayMs?: number;
}

const MIN_DELAY_MS = 4_000;
const MAX_DELAY_MS = 60_000;

export const startImportPoll = ({
	fetchState,
	onState,
	onSettled,
	minDelayMs = MIN_DELAY_MS,
	maxDelayMs = MAX_DELAY_MS
}: ImportPollOptions): (() => void) => {
	let delay = minDelayMs;
	let timer: ReturnType<typeof setTimeout> | undefined;
	let cancelled = false;

	const recheck = async () => {
		const next = await fetchState();
		if (cancelled) return;
		// a null answer means the import finished and bobbin dropped the record; reporting it is what
		// dismisses the banner, so it must not be skipped
		onState(next);
		if (!next || next.content === "failed") {
			onSettled?.();
			return;
		}
		delay = Math.min(delay * 2, maxDelayMs);
		timer = setTimeout(recheck, delay);
	};

	timer = setTimeout(recheck, delay);
	return () => {
		cancelled = true;
		if (timer) clearTimeout(timer);
	};
};