function urlBase64ToUint8Array(base64String: string) {
  const padding = "=".repeat((4 - (base64String.length % 4)) % 4);
  const base64 = (base64String + padding).replace(/-/g, "+").replace(/_/g, "/");
  const rawData = window.atob(base64);
  const outputArray = new Uint8Array(rawData.length);
  for (let i = 0; i < rawData.length; ++i) {
    outputArray[i] = rawData.charCodeAt(i);
  }
  return outputArray;
}

export function isPushSupported(): boolean {
  return "serviceWorker" in navigator && "PushManager" in window;
}

export async function getExistingSubscription(): Promise<PushSubscription | null> {
  if (!isPushSupported()) return null;
  try {
    const reg = await navigator.serviceWorker.getRegistration("/sw.js");
    if (reg) return await reg.pushManager.getSubscription();
  } catch {}
  return null;
}

export async function subscribeToPush(): Promise<boolean> {
  const keyRes = await fetch("/api/push/vapid-key");
  const { publicKey } = await keyRes.json();
  if (!publicKey) throw new Error("VAPID key not configured");

  const reg = await navigator.serviceWorker.register("/sw.js");
  await navigator.serviceWorker.ready;

  const sub = await reg.pushManager.subscribe({
    userVisibleOnly: true,
    applicationServerKey: urlBase64ToUint8Array(publicKey),
  });

  const subJson = sub.toJSON();
  const res = await fetch("/api/push/subscribe", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ endpoint: subJson.endpoint, keys: subJson.keys }),
  });
  if (!res.ok) throw new Error("Subscription save failed");
  return true;
}

export async function unsubscribeFromPush(): Promise<boolean> {
  const reg = await navigator.serviceWorker.getRegistration("/sw.js");
  if (reg) {
    const sub = await reg.pushManager.getSubscription();
    if (sub) {
      const res = await fetch("/api/push/unsubscribe", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ endpoint: sub.endpoint }),
      });
      if (!res.ok) throw new Error("Unsubscribe failed");
      await sub.unsubscribe();
    }
  }
  return true;
}