// Blocking overlay for a daemon that went away — see docs/RESTART.md.
//
// Mounted while the link is `down` or `updating`, torn down the moment it is
// back. It owns no polling of its own: DaemonLink polls, and this only renders
// what the link reports.

import { formatRelease, type DaemonLink, type LinkStatus } from "./daemonLink.js";

export interface RestartOverlayHandle {
  dispose(): void;
}

/** Mount the overlay controller. It stays subscribed for the page's lifetime. */
export function installRestartOverlay(
  link: DaemonLink,
  host: HTMLElement = document.body,
): RestartOverlayHandle {
  let el: HTMLElement | null = null;
  let title: HTMLElement | null = null;
  let detail: HTMLElement | null = null;
  let release: HTMLElement | null = null;

  const unsubscribe = link.subscribe((status) => render(status));

  function render(status: LinkStatus): void {
    const blocking = status.state === "down" || status.state === "updating";
    if (!blocking) {
      unmount();
      return;
    }
    if (!el) mount();
    const updating = status.state === "updating";
    title!.textContent = updating ? "Maestro was updated" : "Maestro is restarting";
    detail!.textContent = updating
      ? "Reloading this page onto the new release…"
      : attemptText(status.attempts);
    release!.textContent = formatRelease(status.build);
  }

  /** The poll runs while this is up; saying how many tries have gone by is what
   *  separates "still restarting" from "wedged" for someone staring at it. */
  function attemptText(attempts: number): string {
    if (attempts <= 1) return "Waiting for the daemon to come back…";
    return `Waiting for the daemon to come back… (${attempts} attempts)`;
  }

  function mount(): void {
    el = document.createElement("div");
    el.className = "modal-backdrop restart-backdrop";
    const dialog = document.createElement("div");
    dialog.className = "modal restart-modal";
    dialog.setAttribute("role", "alertdialog");
    dialog.setAttribute("aria-modal", "true");
    dialog.setAttribute("aria-labelledby", "restart-title");

    title = document.createElement("h2");
    title.id = "restart-title";
    detail = document.createElement("p");
    detail.className = "restart-detail";
    release = document.createElement("p");
    release.className = "restart-release";
    const spinner = document.createElement("div");
    spinner.className = "restart-spinner";
    spinner.setAttribute("aria-hidden", "true");

    dialog.append(spinner, title, detail, release);
    el.appendChild(dialog);
    host.appendChild(el);
    // The app's shortcuts live on `window`, so hiding the UI behind a backdrop
    // does not stop them: `n` would still open a spawn form against a daemon
    // that is not there. Swallow keys in the capture phase until the link is
    // back, without `preventDefault` so the browser's own chords still work.
    window.addEventListener("keydown", swallow, true);
  }

  function swallow(e: KeyboardEvent): void {
    e.stopImmediatePropagation();
  }

  function unmount(): void {
    if (!el) return;
    window.removeEventListener("keydown", swallow, true);
    el.remove();
    el = null;
  }

  return {
    dispose(): void {
      unsubscribe();
      unmount();
    },
  };
}