add firebase and sign up

src/lib/auth/userStore.svelte.js

@@ -0,0 +1,72 @@
+import { auth, db, googleProvider } from '../firebase.js';
+import { onAuthStateChanged, signInWithPopup, signOut as fbSignOut } from 'firebase/auth';
+import { doc, getDoc, setDoc, serverTimestamp } from 'firebase/firestore';
+import { initSelectionListener } from '../layout/selection.svelte.js';
+import { initEntriesListener } from '../stores/entriesStore.svelte.js';
+
+let _initialized = false;
+
+let user = $state(null);
+let userProfile = $state(null);
+let loading = $state(true);
+let needsCountry = $state(false);
+
+export function getUser() { return user; }
+export function getUserProfile() { return userProfile; }
+export function getLoading() { return loading; }
+export function getNeedsCountry() { return needsCountry; }
+
+export async function signInWithGoogle() {
+  await signInWithPopup(auth, googleProvider);
+}
+
+export async function signOut() {
+  await fbSignOut(auth);
+  user = null;
+  userProfile = null;
+  needsCountry = false;
+}
+
+export async function setHomeCountry(country) {
+  if (!user) return;
+  await setDoc(doc(db, 'users', user.uid), {
+    displayName: user.displayName,
+    photoURL: user.photoURL,
+    email: user.email,
+    homeCountry: country,
+    visitedCountries: [],
+    createdAt: serverTimestamp(),
+  });
+  userProfile = { ...userProfile, homeCountry: country, visitedCountries: [] };
+  needsCountry = false;
+}
+
+export function initAuth() {
+  if (_initialized) return;
+  _initialized = true;
+  onAuthStateChanged(auth, async (fbUser) => {
+    if (fbUser) {
+      user = fbUser;
+      initSelectionListener(fbUser.uid);
+      initEntriesListener(fbUser.uid);
+      const docRef = doc(db, 'users', fbUser.uid);
+      const docSnap = await getDoc(docRef);
+      if (docSnap.exists()) {
+        userProfile = docSnap.data();
+        needsCountry = false;
+      } else {
+        userProfile = {
+          displayName: fbUser.displayName,
+          photoURL: fbUser.photoURL,
+          email: fbUser.email,
+        };
+        needsCountry = true;
+      }
+    } else {
+      user = null;
+      userProfile = null;
+      needsCountry = false;
+    }
+    loading = false;
+  });
+}