Add Web Push warning notification backend

lib/notification-api.ts

@@ -0,0 +1,43 @@
+import type { Language } from "@/lib/i18n";
+import type { Province } from "@/types/province";
+
+interface VapidKeyResponse {
+  configured: boolean;
+  publicKey: string | null;
+}
+
+export async function fetchVapidPublicKey(signal?: AbortSignal) {
+  const response = await fetch("/api/notifications/vapid-key", { signal });
+  if (!response.ok) throw new Error("Unable to load Web Push configuration.");
+  return response.json() as Promise<VapidKeyResponse>;
+}
+
+export async function savePushSubscription(subscription: PushSubscription, province: Province, language: Language) {
+  const response = await fetch("/api/notifications/subscriptions", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify({
+      subscription: subscription.toJSON(),
+      province,
+      language,
+      enabled: true,
+    }),
+  });
+  if (!response.ok) throw new Error("Unable to save push subscription.");
+}
+
+export async function deletePushSubscription(endpoint: string) {
+  const response = await fetch("/api/notifications/subscriptions", {
+    method: "DELETE",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify({ endpoint }),
+  });
+  if (!response.ok) throw new Error("Unable to delete push subscription.");
+}
+
+export function decodeBase64UrlKey(value: string) {
+  const padding = "=".repeat((4 - (value.length % 4)) % 4);
+  const base64 = `${value}${padding}`.replace(/-/g, "+").replace(/_/g, "/");
+  const raw = window.atob(base64);
+  return Uint8Array.from(raw, (character) => character.charCodeAt(0));
+}