/**
 * Fan-out helper used wherever PhotoPrism lacks a true batch endpoint.
 * Bounded concurrency keeps the indexer happy on slow hosts; each item's
 * result is collected and the aggregate `{updated, errors[]}` mirrors the
 * shape the legacy mule-image bulk endpoint returned, so existing toast
 * + undo plumbing slots in without changes.
 */

export interface BatchResult<T> {
	updated: T[];
	errors: { id: string; message: string }[];
}

export interface BatchOptions {
	concurrency?: number;
	onProgress?: (done: number, total: number, completedId: string) => void;
}

export async function batchEdit<T>(
	ids: string[],
	fn: (id: string) => Promise<T>,
	opts: BatchOptions = {}
): Promise<BatchResult<T>> {
	const concurrency = Math.max(1, opts.concurrency ?? 8);
	const updated: T[] = [];
	const errors: { id: string; message: string }[] = [];
	let i = 0;
	let done = 0;

	async function worker() {
		while (true) {
			const idx = i++;
			if (idx >= ids.length) return;
			const id = ids[idx];
			try {
				updated.push(await fn(id));
			} catch (err) {
				errors.push({ id, message: err instanceof Error ? err.message : String(err) });
			} finally {
				done++;
				opts.onProgress?.(done, ids.length, id);
			}
		}
	}

	await Promise.all(
		Array.from({ length: Math.min(concurrency, ids.length) }, () => worker())
	);
	return { updated, errors };
}