// Islands infrastructure.
//
// An "island" is a custom element that attaches behavior to server-rendered
// markup — it never re-renders the server's HTML (no hydration). A key payoff
// over the old `querySelectorAll` + `DOMContentLoaded` + `htmx:afterSwap`
// re-init dance: the browser upgrades a custom element automatically whenever
// it's connected to the document, INCLUDING content HTMX swaps in, so islands
// need no manual re-initialization after a swap.
//
// Pure, testable logic goes in a sibling `*.logic.ts` (no DOM imports) so
// `node --test` can exercise it without a DOM; the element file wires that
// logic over the light-DOM children.

/** Base class: runs `init()` exactly once, the first time the element is
 *  connected (a move/reconnect won't re-run it). */
export abstract class MnwElement extends HTMLElement {
  #initialized = false;

  connectedCallback(): void {
    if (this.#initialized) return;
    this.#initialized = true;
    this.init();
  }

  /** Wire behavior over the already-rendered light-DOM children. */
  protected abstract init(): void;
}

/** Define a custom element once (idempotent — safe if the module is imported
 *  from more than one entry). */
export function define(name: string, ctor: CustomElementConstructor): void {
  if (!customElements.get(name)) customElements.define(name, ctor);
}