// Pure string logic for zettelclean. No Obsidian imports, so it is unit-testable
// in isolation. The transform is always one-way (H1 -> filename), which lets us
// freely drop characters without worrying about a reverse mapping.

// A TIMEID is a leading run of 12 to 18 digits, ending at a dash or end-of-name.
// 12-18 because collision-avoidance may append extra digits to a 14-digit stamp.
const TIMEID_RE = /^(\d{12,18})(?=-|$)/;

// Return the immutable id prefix, or null if this file is not a zettel.
export function extractTimeId(basename: string): string | null {
	const m = basename.match(TIMEID_RE);
	return m?.[1] ?? null;
}

// H1 text -> kebab slug. sanifize as inspiration, deliberately simpler.
export function generateSlug(heading: string): string {
	return heading
		.normalize('NFKD') // split accented letters into base + combining mark
		.replace(/[̀-ͯ]/g, '') // strip the combining marks (c-cedilla -> c)
		.toLowerCase()
		.replace(/[^a-z0-9]+/g, '-') // any run of non-alphanumerics -> one dash
		.replace(/^-+|-+$/g, ''); // trim leading/trailing dashes
}

// Reassemble; an empty slug collapses to the bare id.
export function buildFilename(id: string, slug: string): string {
	return slug ? `${id}-${slug}` : id;
}