import { get, post } from "./api";

function b64ToBytes(b64: string): Uint8Array<ArrayBuffer> {
  const s = atob(b64.replace(/-/g, "+").replace(/_/g, "/") + "===".slice((b64.length + 3) % 4));
  const out = new Uint8Array(new ArrayBuffer(s.length));
  for (let i = 0; i < s.length; i++) out[i] = s.charCodeAt(i);
  return out;
}

export const pushSupported = () => "serviceWorker" in navigator && "PushManager" in window && "Notification" in window;

/** Current push subscription of this device (null if none). */
export async function currentSubscription(): Promise<PushSubscription | null> {
  if (!pushSupported()) return null;
  const reg = await navigator.serviceWorker.ready;
  return reg.pushManager.getSubscription();
}

/** Ask for permission, subscribe this device and register it with the server. */
export async function enablePush(): Promise<void> {
  if (!pushSupported()) throw new Error("Push is not supported by this browser (on iOS: install the app to the home screen first).");
  const perm = await Notification.requestPermission();
  if (perm !== "granted") throw new Error("Notifications were not allowed.");
  const reg = await navigator.serviceWorker.ready;
  const { key } = await get<{ key: string }>("/push/key");
  let sub = await reg.pushManager.getSubscription();
  // A subscription for another server key must be replaced.
  if (sub && sub.options.applicationServerKey) {
    const cur = new Uint8Array(sub.options.applicationServerKey);
    const want = b64ToBytes(key);
    if (cur.length !== want.length || cur.some((b, i) => b !== want[i])) {
      await sub.unsubscribe();
      sub = null;
    }
  }
  if (!sub) sub = await reg.pushManager.subscribe({ userVisibleOnly: true, applicationServerKey: b64ToBytes(key) });
  await post("/push/subscribe", sub.toJSON());
  localStorage.setItem("codecraft.push", "1");
}

export async function disablePush(): Promise<void> {
  const sub = await currentSubscription();
  if (sub) {
    await fetch("/api/push/subscribe", { method: "DELETE", credentials: "same-origin", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ endpoint: sub.endpoint }) });
    await sub.unsubscribe();
  }
  localStorage.removeItem("codecraft.push");
}

/** Re-register this device's existing subscription with the server (idempotent). */
export async function syncPush(): Promise<boolean> {
  const sub = await currentSubscription().catch(() => null);
  if (!sub) return false;
  await post("/push/subscribe", sub.toJSON());
  localStorage.setItem("codecraft.push", "1");
  return true;
}

export async function testPush(): Promise<{ sent: number; errors: string[] }> {
  // Make sure the server knows this device before testing.
  await syncPush();
  return post<{ sent: number; errors: string[] }>("/push/test", {});
}