import { ownerDocument } from "../dom/owner-document.ts";
import { DISABLE_SCROLLBAR_STYLE } from "./style-disable-scrollbar.ts";

/**
 * Per-document ref-counted disable-scrollbar style registration.
 *
 * Each `<ScrollArea.Root>` would otherwise inject its own `<style>` tag with
 * identical CSS — multiple roots on the page give you N copies of the same
 * rules. This helper installs a single `<style>` per document (keyed by the
 * element's owning document so shadow roots and iframe documents don't
 * cross-pollute with the main document) and increments a counter for every
 * mount; only the last unmount removes the tag.
 *
 * Shadow-DOM note: `ownerDocument` walks up to the owning `Document` (not
 * the shadow-root), so a style registered from inside a shadow tree still
 * lives in the owning document's `<head>`. This matches the rest of the
 * `internals/dom/` utilities.
 */

const ATTRIBUTE = "data-quoin-scroll-area-disable";

interface Entry {
	count: number;
	element: HTMLStyleElement;
}

const registry = new WeakMap<Document, Entry>();

export function registerDisableScrollbarStyle(
	anchor: Node | null | undefined,
	nonce: string | undefined,
): () => void {
	const doc = ownerDocument(anchor);

	let entry = registry.get(doc);
	if (entry == null) {
		// Look for an existing tag injected by a prior registration that lost
		// its WeakMap entry (e.g. during HMR). Reuse it rather than stacking.
		const existing = doc.querySelector<HTMLStyleElement>(`style[${ATTRIBUTE}]`);
		const element = existing ?? doc.createElement("style");
		if (existing == null) {
			element.setAttribute(ATTRIBUTE, "");
			if (nonce) element.setAttribute("nonce", nonce);
			element.textContent = DISABLE_SCROLLBAR_STYLE;
			doc.head.appendChild(element);
		}
		entry = { count: 0, element };
		registry.set(doc, entry);
	}

	entry.count += 1;

	return () => {
		const current = registry.get(doc);
		if (current == null) return;
		current.count -= 1;
		if (current.count <= 0) {
			current.element.remove();
			registry.delete(doc);
		}
	};
}