import type { components } from '$lib/generated/api';
import { fillDensityGaps, type MonthBucket } from '$lib/shared/utils/monthBuckets';

type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];

/**
 * A year band with more letters than this renders as a compact density strip
 * (count + 12-month sparkline) instead of one card per letter (REQ-012).
 */
export const DENSE_THRESHOLD = 12;

export function isDense(letterCount: number): boolean {
	return letterCount > DENSE_THRESHOLD;
}

/**
 * Buckets a band's letters into exactly 12 month buckets (`{year}-01`..`{year}-12`)
 * for the density sparkline. Each letter counts on its `eventDate` month; coarser
 * precisions (SEASON/YEAR/APPROX) count on whatever anchor month the backend put
 * in `eventDate`. Entries without an `eventDate` (e.g. UNKNOWN) are ignored — they
 * live in the "Ohne Datum" bucket, not a dated band. (REQ-027)
 */
export function monthHistogram(letters: TimelineEntryDTO[], year: number): MonthBucket[] {
	const counts = new Map<string, number>();
	for (const l of letters) {
		if (!l.eventDate) continue;
		const month = l.eventDate.slice(0, 7); // YYYY-MM
		counts.set(month, (counts.get(month) ?? 0) + 1);
	}
	const buckets = Array.from(counts.entries()).map(([month, count]) => ({ month, count }));
	return fillDensityGaps(buckets, `${year}-01-01`, `${year}-12-31`);
}