add functions

firebase.json

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+{
+  "functions": [
+    {
+      "source": "functions",
+      "codebase": "default",
+      "ignore": [
+        "node_modules",
+        ".git",
+        "firebase-debug.log",
+        "firebase-debug.*.log"
+      ]
+    }
+  ]
+}

functions/.gitignore

@@ -0,0 +1 @@
+node_modules/

functions/index.js

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+import * as functions from 'firebase-functions';
+import * as admin from 'firebase-admin';
+import CryptoJS from 'crypto-js';
+
+admin.initializeApp();
+
+const db = admin.firestore();
+
+const initialPlayerStats = {
+  gamesPlayed: 0,
+  lastPlayed: "",
+  currentStreak: 0,
+  guesses: {
+    1: 0,
+    2: 0,
+    3: 0,
+    4: 0,
+    5: 0,
+    failed: 0,
+  },
+};
+
+exports.saveNewUser = functions.auth.user().onCreate(async (user) => {
+  const uid = user.uid;
+  const email = user.email || '';
+  const username = user.displayName || '';
+
+  const emailHash = CryptoJS.MD5(email).toString();
+  const userRef = db.collection('users').doc(uid);
+  const usernameRef = db.collection('usernames').doc(username);
+
+  const batch = db.batch();
+
+  batch.set(userRef, {
+    email,
+    username,
+    stats: initialPlayerStats,
+    emailHash,
+    lastUpdatedUsername: admin.firestore.FieldValue.serverTimestamp(),
+  });
+
+  batch.set(usernameRef, { uid });
+
+  await batch.commit();
+});