/**
 * Islands infrastructure.
 *
 * An island is a custom element that attaches behavior to server-rendered
 * markup. It never re-renders what the server sent, so a page keeps working
 * with the script blocked and the element only adds what needs a client.
 *
 * The payoff over the `DOMContentLoaded` + `htmx:after:swap` re-init dance that
 * static/mt.js does by hand: the browser upgrades a custom element whenever it
 * is connected to the document, including markup htmx swapped in, so an island
 * needs no manual re-initialization.
 *
 * Ported from MNW/server/frontend/src/islands/base.ts, deliberately as a copy.
 * The two apps share no workspace and no registry, and 30 lines duplicated is
 * cheaper than the mechanism that would let them share it. See the Client
 * section of the livechat design note.
 *
 * Pure logic goes in a sibling `*.logic.ts` with no DOM imports, so
 * `node --test` exercises 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. Moving the element in the document will not re-run it.
 */
export abstract class MtElement 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, so importing the module from more
 * than one entry point does not throw on the second definition.
 */
export function define(name: string, ctor: CustomElementConstructor): void {
  if (!customElements.get(name)) customElements.define(name, ctor);
}