// Obsidian's charset for author-typed block ids: letters, digits and dashes.
const BLOCK_ID = "[A-Za-z0-9][A-Za-z0-9-]*";

// "some text ^my-id" — the marker closing a block.
export const TRAILING_BLOCK_ID_RE = new RegExp(`\\s\\^(${BLOCK_ID})$`);
// "^my-id" alone on the line after a block.
export const STANDALONE_BLOCK_ID_RE = new RegExp(`^\\^(${BLOCK_ID})$`);

const BLOCK_ID_RE = new RegExp(`^${BLOCK_ID}$`);

// The anchor keeps the caret: toSlug eats it, so no heading anchor can ever collide
// with a block id. Browsers percent-decode a fragment before matching ids, so `#^id`
// still finds `id="^id"`.
export function blockAnchor(id: string): string | null {
	return BLOCK_ID_RE.test(id) ? `^${id}` : null;
}