import { initializeApp } from 'firebase/app';
import { getFirestore, collection, addDoc, serverTimestamp } from 'firebase/firestore';
import { getAuth } from 'firebase/auth';

const firebaseConfig = {
    apiKey: "AIzaSyD-YOUR-API-KEY",
    authDomain: "app-prod.firebaseapp.com",
    projectId: "app-prod",
    storageBucket: "app-prod.appspot.com",
};

// Tree-shakeable modular SDK initialization in Firebase v10+
const app = initializeApp(firebaseConfig);
export const db = getFirestore(app);
export const auth = getAuth(app);

// ACID Atomic Transaction with Optimistic Concurrency Control (OCC)
import { runTransaction, doc } from 'firebase/firestore';

async function transferFunds(senderId, receiverId, amount) {
    await runTransaction(db, async (transaction) => {
        const senderDocRef = doc(db, 'wallets', senderId);
        const receiverDocRef = doc(db, 'wallets', receiverId);

        const senderSnapshot = await transaction.get(senderDocRef);
        const currentBalance = senderSnapshot.data().balance;

        if (currentBalance < amount) {
            throw new Error("Insufficient funds for transaction");
        }

        // Atomic write operations (Guaranteed zero financial double-spend race conditions!)
        transaction.update(senderDocRef, { balance: currentBalance - amount });
        transaction.update(receiverDocRef, { balance: (receiverDocRef.balance || 0) + amount });
    });
}

// firestore.rules - Enterprise Declarative Security Rules
rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {

    function isAuthenticated() {
      return request.auth != null;
    }

    function isOwner(userId) {
      return isAuthenticated() && request.auth.uid == userId;
    }

    function isAdmin() {
      return isAuthenticated() && request.auth.token.role == 'admin';
    }

    match /users/{userId} {
      allow read: if isAuthenticated();
      allow write: if isOwner(userId) || isAdmin();
    }

    match /orders/{orderId} {
      allow read: if isAuthenticated() && resource.data.customerId == request.auth.uid;
      allow create: if isAuthenticated() && 
                    request.resource.data.customerId == request.auth.uid &&
                    request.resource.data.amount > 0;
      allow update, delete: if isAdmin();
    }
  }
}

// Setting Custom User Claims via Firebase Admin SDK (Node.js Server)
import admin from 'firebase-admin';

export async function grantAdminRole(targetUid) {
    // Injects claims directly into user's signed JWT token!
    await admin.auth().setCustomUserClaims(targetUid, {
        role: 'admin',
        tier: 'enterprise',
        canManageBilling: true
    });
    console.log(`Successfully elevated user ${targetUid} to Admin`);
}