/** Adds or removes a custom state, which CSS matches as `:state(name)`. */
export function setState(internals: ElementInternals, name: string, on: boolean): void {
  if (on) internals.states.add(name);
  else internals.states.delete(name);
}

/**
 * Defines a custom element unless a hot reload already did. Elements defined here keep their shadow
 * styles when moved into another document (a torn-off panel's popup): see `adopt`.
 */
export function define(name: string, constructor: CustomElementConstructor): void {
  if (customElements.get(name)) return;
  const own = constructor.prototype.adoptedCallback as ((...args: unknown[]) => void) | undefined;
  constructor.prototype.adoptedCallback = function (this: HTMLElement, ...args: unknown[]) {
    if (this.shadowRoot) restyle(this.shadowRoot);
    own?.apply(this, args);
  };
  customElements.define(name, constructor);
}

/** Builds a constructable stylesheet for a shadow root. */
export function sheet(css: string): CSSStyleSheet {
  const result = new CSSStyleSheet();
  result.replaceSync(css);
  return result;
}

const adopted = new WeakMap<ShadowRoot, readonly CSSStyleSheet[]>();
const copies = new WeakMap<CSSStyleSheet, WeakMap<Document, CSSStyleSheet>>();

/**
 * Sets a shadow root's stylesheets. Use it instead of assigning `adoptedStyleSheets`: every engine
 * empties that list when a node moves to another document, and refuses a sheet constructed in a
 * different one, so `define`'s `adoptedCallback` re-adopts these as copies built in the new document.
 */
export function adopt(root: ShadowRoot, ...sheets: CSSStyleSheet[]): void {
  adopted.set(root, sheets);
  restyle(root);
}

function restyle(root: ShadowRoot): void {
  const sheets = adopted.get(root);
  if (sheets) root.adoptedStyleSheets = sheets.map((original) => inDocument(original, root.ownerDocument));
}

/** `original`, or a copy constructed in `doc` when `original` belongs to another document. */
function inDocument(original: CSSStyleSheet, doc: Document): CSSStyleSheet {
  const view = doc.defaultView;
  if (!view || doc === document) return original;
  let byDocument = copies.get(original);
  if (!byDocument) copies.set(original, (byDocument = new WeakMap()));
  let copy = byDocument.get(doc);
  if (!copy) {
    copy = new view.CSSStyleSheet();
    copy.replaceSync([...original.cssRules].map((rule) => rule.cssText).join("\n"));
    byDocument.set(doc, copy);
  }
  return copy;
}