siftlode/frontend/src/lib/fullscreen.ts

import {
  useEffect,
  useInsertionEffect,
  useLayoutEffect,
  useState,
  useSyncExternalStore,
} from "react";

// The browser's Fullscreen API, WebKit included.
//
// Safari and iPadOS still ship only the prefixed spelling: no `fullscreenchange`, no
// `fullscreenElement`, no `requestFullscreen` on a plain element. Reading only the unprefixed names
// there means the page believes it is NEVER fullscreen — which silently breaks whatever the
// fullscreen state drives (an overlay that must yield, a focus reclaim, an Esc branch that would
// otherwise close the whole player instead of just leaving fullscreen).
//
// Both video surfaces (PlayerModal's YouTube embed, PlexPlayer's <video>) go through here, so the
// prefix handling lives in ONE place — the previous shape had it in neither, then in one.

type WebkitDocument = Document & {
  webkitFullscreenElement?: Element | null;
  webkitExitFullscreen?: () => void;
};
type WebkitElement = HTMLElement & { webkitRequestFullscreen?: () => void };

/** The element currently holding the fullscreen lock, or null. */
export function fullscreenElement(): Element | null {
  const d = document as WebkitDocument;
  return d.fullscreenElement ?? d.webkitFullscreenElement ?? null;
}

/** Ask for fullscreen on `el`. Errors are swallowed on purpose: a refused request (no user
 * activation, an iOS device that only fullscreens <video>) is not something a caller can fix. */
export function requestFullscreen(el: HTMLElement): void {
  const e = el as WebkitElement;
  if (e.requestFullscreen) void e.requestFullscreen().catch(() => {});
  else e.webkitRequestFullscreen?.();
}

/** Leave fullscreen, whoever holds it. */
export function exitFullscreen(): void {
  const d = document as WebkitDocument;
  if (d.exitFullscreen) void d.exitFullscreen().catch(() => {});
  else d.webkitExitFullscreen?.();
}

/** Subscribe to fullscreen transitions; returns the unsubscribe. Registers BOTH spellings — a
 * browser that supports both never fires both for the same transition, so the handler still runs
 * once. */
export function onFullscreenChange(handler: () => void): () => void {
  document.addEventListener("fullscreenchange", handler);
  document.addEventListener("webkitfullscreenchange", handler);
  return () => {
    document.removeEventListener("fullscreenchange", handler);
    document.removeEventListener("webkitfullscreenchange", handler);
  };
}

// `fullscreenElement()` returns the live DOM node, so the same element is the same reference across
// calls — a valid useSyncExternalStore snapshot without any caching of our own.
const fsSnapshot = () => fullscreenElement() as HTMLElement | null;
const fsServerSnapshot = () => null;

/** The fullscreen element as reactive state, for code that must RENDER differently while something
 *  holds the lock — today only `useFullscreenPortalHost` below, which has to portal INTO that element
 *  (a node portaled to <body> is painted underneath the fullscreen element, i.e. invisible).
 *  Components that merely react to the transition should keep using `onFullscreenChange` directly. */
function useFullscreenElement(): HTMLElement | null {
  return useSyncExternalStore(onFullscreenChange, fsSnapshot, fsServerSnapshot);
}

/** ONE container div for an overlay's whole life, re-parented between `<body>` and the fullscreen
 *  element instead of handed to `createPortal` as a changing container: React tears a portal down
 *  and builds it again when its container changes, and the overlay's contents go with it (a
 *  half-filled form reset to its defaults the moment the viewer left true fullscreen).
 *
 *  Two rules this owns, which the two hand-written copies it replaced disagreed about (deep-review
 *  round 5):
 *
 *  1. **It is attached BEFORE the portal's children commit.** `useInsertionEffect` runs in the
 *     mutation phase, and React handles `autoFocus` in `commitMount` during the LAYOUT phase — one
 *     whole phase later. Attaching in a `useLayoutEffect` is too late: layout effects commit
 *     children-before-parent, so every `autoFocus` descendant called `.focus()` on a node that was
 *     still disconnected, where `focus()` is a no-op. Every autoFocus in every dialog was dead.
 *  2. **`appendChild` MOVES the node, it does not teleport it.** Per the DOM spec an already-parented
 *     node is removed and re-inserted, and removing a focused element's ancestor resets focus to
 *     `<body>` — so the focused element is saved and re-focused across the move.
 */
export function useFullscreenPortalHost(): HTMLElement | null {
  const fsRoot = useFullscreenElement();
  const [host] = useState<HTMLElement | null>(() =>
    typeof document === "undefined" ? null : document.createElement("div"),
  );
  useInsertionEffect(() => {
    if (host && !host.parentNode) document.body.appendChild(host);
  }, [host]);
  useLayoutEffect(() => {
    if (!host) return;
    const parent = fsRoot ?? document.body;
    if (host.parentNode === parent) return;
    const focused = host.contains(document.activeElement)
      ? (document.activeElement as HTMLElement)
      : null;
    parent.appendChild(host);
    focused?.focus();
  }, [fsRoot, host]);
  useEffect(() => () => host?.remove(), [host]);
  return host;
}