import { desktopBridge } from "./desktop";
import { rpc } from "./rpc";

const SERVICE_WORKER_URL = "/sw.js";
const SERVICE_WORKER_SCOPE = "/";

/**
 * Web push needs the Push API, a service worker and a secure context (https or localhost). The
 * desktop app keeps its in-app notifications instead.
 */
export function webPushSupported(): boolean {
  return (
    typeof window !== "undefined" &&
    window.isSecureContext &&
    "serviceWorker" in navigator &&
    "PushManager" in window &&
    "Notification" in window &&
    !desktopBridge()
  );
}

/** Registers the push service worker where web push works; safe to call on every start. */
export async function registerPushServiceWorker(): Promise<void> {
  if (!webPushSupported()) return;
  await navigator.serviceWorker
    .register(SERVICE_WORKER_URL, { scope: SERVICE_WORKER_SCOPE })
    .catch(() => undefined);
}

async function currentSubscription(): Promise<PushSubscription | null> {
  const registration = await navigator.serviceWorker.getRegistration(SERVICE_WORKER_SCOPE);
  return (await registration?.pushManager.getSubscription()) ?? null;
}

/** True when this browser has granted notifications and holds a push subscription. */
export async function webPushEnabled(): Promise<boolean> {
  if (!webPushSupported() || Notification.permission !== "granted") return false;
  return Boolean(await currentSubscription().catch(() => null));
}

function base64UrlToBytes(value: string): Uint8Array<ArrayBuffer> {
  const base64 = value.replace(/-/g, "+").replace(/_/g, "/");
  const binary = atob(base64.padEnd(Math.ceil(base64.length / 4) * 4, "="));
  const bytes = new Uint8Array(new ArrayBuffer(binary.length));
  for (let index = 0; index < binary.length; index += 1) bytes[index] = binary.charCodeAt(index);
  return bytes;
}

function sameKey(current: ArrayBuffer | null, expected: Uint8Array): boolean {
  if (!current || current.byteLength !== expected.byteLength) return false;
  const bytes = new Uint8Array(current);
  return bytes.every((byte, index) => byte === expected[index]);
}

/**
 * Turns on push for this browser and registers it with the server. Call it straight from a click:
 * browsers only show the permission prompt during a user gesture. Throws when the server cannot
 * be reached.
 */
export async function enableWebPush(): Promise<"enabled" | "denied" | "unsupported"> {
  if (!webPushSupported()) return "unsupported";
  const permission =
    Notification.permission === "default"
      ? await Notification.requestPermission()
      : Notification.permission;
  if (permission !== "granted") return "denied";
  const config = await rpc.notifications.webPush.config();
  if (!config.available || !config.publicKey) return "unsupported";
  const applicationServerKey = base64UrlToBytes(config.publicKey);
  let subscription: PushSubscription;
  try {
    await navigator.serviceWorker.register(SERVICE_WORKER_URL, { scope: SERVICE_WORKER_SCOPE });
    const registration = await navigator.serviceWorker.ready;
    const existing = await registration.pushManager.getSubscription();
    // A subscription made for other server keys cannot receive this server's pushes.
    if (existing && !sameKey(existing.options.applicationServerKey, applicationServerKey)) {
      await existing.unsubscribe();
    }
    subscription =
      existing && sameKey(existing.options.applicationServerKey, applicationServerKey)
        ? existing
        : await registration.pushManager.subscribe({ userVisibleOnly: true, applicationServerKey });
  } catch {
    // Browsers without a push service (or with it switched off) reject the subscription.
    return "unsupported";
  }
  const keys = subscription.toJSON().keys ?? {};
  await rpc.notifications.webPush.subscribe({
    endpoint: subscription.endpoint,
    keys: { p256dh: keys.p256dh ?? "", auth: keys.auth ?? "" },
  });
  return "enabled";
}

/** Stops push for this browser, on the server first so no push arrives after it returns. */
export async function disableWebPush(): Promise<void> {
  if (!webPushSupported()) return;
  const subscription = await currentSubscription();
  if (!subscription) return;
  await rpc.notifications.webPush.unsubscribe({ endpoint: subscription.endpoint });
  await subscription.unsubscribe().catch(() => undefined);
}