Architecture

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Technology Stack

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Frontend Stack

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Key Dependencies

• Expo Router (v6.0.22) - File-based routing system
• React (v19.1.0) - UI framework
• Zustand (v5.0.9) - State management
• Zod (v4.3.6) - Schema validation
• React Native Reanimated (v4.1.1) - Animations
• Expo Notifications (v0.32.16) - Push notifications

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Backend Stack

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Appwrite Services

• Account - User authentication and session management
• TablesDB - Database operations
• Functions - Serverless compute
• Storage - File and media management
• Messaging - Push notification delivery
• Teams - Group management capabilities

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Application Structure

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File-Based Routing

app/
├── _layout.tsx          # Root layout with auth & notifications
├── (auth)/              # Authentication flow
├── (tabs)/              # Main tab navigation
│   ├── index.tsx        # Home/Feed
│   ├── rooms.tsx        # Live chat rooms
│   ├── create.tsx       # Create posts
│   └── profile.tsx      # User profile
└── [dynamic]/           # Dynamic routes

export default function RootLayout() {
  const [user, setUser] = useState<Models.User<Models.Preferences> | null>(null);

  useEffect(() => {
    (async () => {
      const userData = await account.get();
      setUser(userData);
      setUsername(userData.name || userData.email.split("@")[0]);
      setFavTeam(userData.prefs?.favTeam || "None");
      setEmail(userData.email);
      setJoinDate(new Date(userData.$createdAt));
    })();
  }, []);

  // Notification handler configuration
  Notifications.setNotificationHandler({
    handleNotification: async () => ({
      shouldPlaySound: true,
      shouldSetBadge: true,
      shouldShowBanner: true,
      shouldShowList: true,
    }),
  });

  return (
    <>
      <Stack screenOptions={{ headerShown: false }} />
      <Toast />
    </>
  );
}

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State Management

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Zustand Stores

type UserType = {
  username: string | null;
  email: string | null;
  favTeam: string | null;
  messageCount: number;
  joinDate: Date;
  setUsername: (username: string) => void;
  setEmail: (email: string) => void;
  setFavTeam: (favTeam: string) => void;
  setMessageCount: (count: number) => void;
  setJoinDate: (date: Date) => void;
};

type PostsType = {
  posts: Post[];
  setPosts: (posts: Post[]) => void;
  addPost: (post: Post) => void;
  addPosts: (posts: Post[]) => void;
  updatePost: (post: Partial<Post>) => void;
  deletePost: (postId: string) => void;
};

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Backend Architecture

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Appwrite Configuration

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Authentication Flow

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Serverless Functions

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Function Specifications

• Runtime: Node.js 22
• Resources: 0.5 vCPU, 512 MB RAM
• Timeout: 15 seconds
• Execution: Available to any authenticated user
• Scopes: users.read, tables.read, tables.write, rows.read, rows.write

async function rateLimitCheck(activity) {
  const windowKey = Math.floor(Date.now() / 60000); // 1-minute window
  
  const userActivity = await tablesDB.listRows({
    databaseId: CRIC_TALK_DATABASE_ID,
    tableId: RATE_LIMIT_TABLE_ID,
    queries: [
      Query.equal('userId', userId),
      Query.equal('activity', activity),
      Query.equal('windowKey', windowKey),
    ],
  });

  if (userActivity.rows.length === 0) {
    // Create new rate limit entry
    await tablesDB.createRow({
      data: { userId, activity, windowKey, activityCount: 1 }
    });
    return;
  }

  const row = userActivity.rows[0];
  if (row.activityCount >= 10) {
    throw new Error('Rate limit exceeded: Too many requests in a short period.');
  }

  // Increment activity count
  await tablesDB.incrementRowColumn({
    rowId: row.$id,
    column: 'activityCount',
    value: 1,
  });
}

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Real-Time Features

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Appwrite Realtime

• Live Chat Rooms - Real-time message streaming
• Post Feed Updates - New posts appear instantly
• Notification Delivery - In-app notifications
• Like/Comment Counters - Live engagement metrics

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Implementation Pattern

import { client } from '@/libs/appwrite';

// Subscribe to real-time events
const unsubscribe = client.subscribe(
  'databases.{databaseId}.tables.{tableId}.rows',
  (response) => {
    // Handle create, update, delete events
    if (response.events.includes('databases.*.rows.*.create')) {
      // Add new row to state
    }
  }
);

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Push Notifications Architecture

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Expo Notifications Setup

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Notification Types

• New Comment - Someone comments on your post
• Post Like - Someone likes your post
• Room Message - New message in joined chat room
• System Alerts - App announcements and updates

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Rate Limiting Implementation

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Sliding Window Algorithm

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Rate-Limited Activities

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How It Works

1. Window Key Calculation: windowKey = Math.floor(Date.now() / 60000)
2. Activity Lookup: Query rateLimit table for user + activity + windowKey
3. First Request: Create new row with activityCount = 1
4. Subsequent Requests: Increment activityCount if < 10, else reject
5. Window Expiry: Old windows naturally expire as windowKey changes

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Database Design

• posts - User posts with engagement metrics
• comments - Post comments
• rooms - Live chat rooms for matches
• roomMessaage - Chat messages (note: typo in original schema)
• users - Extended user profiles
• notifications - In-app notifications
• rateLimit - Rate limiting tracking