"use client";

import { useSyncExternalStore } from "react";

/**
 * The Settings "reduce motion" toggle (default off). It mirrors the OS
 * preference: the scene stops moving, CSS transitions collapse, and
 * framer-motion runs in its calm mode via MotionPreference. One shared store,
 * so the toggle and every consumer update together.
 */

const KEY = "freezmo.reduce-motion.v1";

let cached: boolean | null = null;
const listeners = new Set<() => void>();

function read(): boolean {
  try {
    return window.localStorage.getItem(KEY) === "1";
  } catch {
    return false;
  }
}

function snapshot(): boolean {
  cached ??= read();
  return cached;
}

export function applyReducedMotion(next: boolean) {
  cached = next;
  document.documentElement.classList.toggle("reduce-motion", next);
  try {
    window.localStorage.setItem(KEY, next ? "1" : "0");
  } catch {
    /* private mode */
  }
  listeners.forEach((listener) => listener());
}

export function useReducedMotionPref() {
  const reduced = useSyncExternalStore(
    (listener) => {
      listeners.add(listener);
      return () => listeners.delete(listener);
    },
    snapshot,
    () => false,
  );
  return { reduced, setReduced: applyReducedMotion };
}