import { ekklesiaDesignTokenStylesheet } from "./registry.js";

/**
 * The attribute that marks a token stylesheet this package installed. Used to make installation
 * idempotent, and to let a host remove exactly what it added.
 */
export const DESIGN_TOKEN_STYLE_ATTRIBUTE = "data-ekklesia-design-tokens";

/**
 * A root that can own a `<style>` element: a whole document, or one artifact's shadow root.
 *
 * Structural rather than nominal (`Document | ShadowRoot`) on purpose. This package must not
 * reference DOM interfaces it does not need, and the two things a caller actually passes differ in
 * everything except these three members.
 */
export interface DesignTokenStyleRoot {
  querySelector(selectors: string): Element | null;
  appendChild<Node_ extends Node>(node: Node_): Node_;
  readonly ownerDocument?: Document | null;
}

function documentFor(root: DesignTokenStyleRoot): Document | undefined {
  if (typeof (root as Partial<Document>).createElement === "function") {
    return root as Document;
  }
  return root.ownerDocument ?? undefined;
}

/**
 * Installs Ekklesia's default token values at a host root, once.
 *
 * Idempotent by construction: a second call finds the element it inserted the first time and
 * updates nothing, so a re-render, a re-mount, or two independent callers can never leave two
 * competing copies of the theme in one root.
 *
 * CSS custom properties **inherit through shadow boundaries**, so installing this at the document
 * root is what makes the same tokens available inside every isolated module artifact without the
 * artifact importing anything or the host reaching into it. A caller that genuinely owns an isolated
 * root with no inheriting ancestor — a standalone display, a test — installs with `scope: "host"`
 * into that root instead.
 *
 * Returns a function that removes exactly the element this call inserted, and nothing else; calling
 * it twice is safe. Returns a no-op when the tokens were already present, so a caller can never
 * uninstall a theme it did not install.
 */
export function installEkklesiaDesignTokens(
  root: DesignTokenStyleRoot,
  options: { readonly scope?: "root" | "host" } = {},
): () => void {
  if (root.querySelector(`style[${DESIGN_TOKEN_STYLE_ATTRIBUTE}]`)) {
    return () => undefined;
  }
  const ownerDocument = documentFor(root);
  if (!ownerDocument) {
    return () => undefined;
  }
  const style = ownerDocument.createElement("style");
  style.setAttribute(DESIGN_TOKEN_STYLE_ATTRIBUTE, "");
  style.textContent = ekklesiaDesignTokenStylesheet(options.scope ?? "root");
  const target =
    (ownerDocument === (root as unknown as Document) ? ownerDocument.head : undefined) ?? root;
  target.appendChild(style);

  let removed = false;
  return () => {
    if (removed) {
      return;
    }
    removed = true;
    style.remove();
  };
}