Skip to content

Firebase Setup & User Tracking

This guide explains how the app implements silent user tracking using Firebase Anonymous Authentication, Cloud Messaging (FCM), and location services.

Overview

The app automatically tracks users without any login or signup. When a user installs and opens the app:

  1. Anonymous Authentication - Assigns a permanent UID
  2. FCM Token - Enables push notifications
  3. Location Tracking - Gets user's current location
  4. Data Storage - Saves to Firebase Firestore

All of this happens silently in the background without user interaction.

Architecture

App Launch
    ↓
UserManager.initializeUser()
    ↓
Firebase Anonymous Auth → UID
    ↓
Firebase Messaging → FCM Token
    ↓
Save to Firestore (uid, fcmToken)
    ↓
Request Location Permissions
    ↓
Get Location → Update Firestore

Implementation Details

1. Firebase Dependencies

Added to app/build.gradle.kts:

// Firebase - Import the BoM
implementation(platform("com.google.firebase:firebase-bom:34.7.0"))

// Firebase products
implementation("com.google.firebase:firebase-analytics")
implementation("com.google.firebase:firebase-auth")           // Anonymous auth
implementation("com.google.firebase:firebase-firestore")      // User data storage
implementation("com.google.firebase:firebase-storage")        // Photo storage
implementation("com.google.firebase:firebase-messaging")      // Push notifications

// Google Play Services for Location
implementation("com.google.android.gms:play-services-location:21.3.0")

// Coil for image loading
implementation("io.coil-kt:coil-compose:2.5.0")

Why each dependency: - firebase-auth: Anonymous user authentication - firebase-firestore: Store user data (UID, FCM token, location) - firebase-storage: Future use for feast photos - firebase-messaging: Receive push notifications - play-services-location: Get user's GPS location - coil: Load images efficiently in Compose

2. Android Manifest Permissions

Added to AndroidManifest.xml:

<!-- Internet permission for Firebase -->
<uses-permission android:name="android.permission.INTERNET" />

<!-- Location permissions for tracking user location -->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

<!-- Notification permission (Android 13+) -->
<uses-permission android:name="android.permission.POST_NOTIFICATIONS" />

Why each permission: - INTERNET: Firebase requires network access - ACCESS_FINE_LOCATION: Get precise GPS coordinates - ACCESS_COARSE_LOCATION: Fallback for approximate location - POST_NOTIFICATIONS: Required for Android 13+ to show notifications

3. Firebase Cloud Messaging Service

Added BhandaraMessagingService.kt:

<!-- In AndroidManifest.xml -->
<service
    android:name=".services.BhandaraMessagingService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

Purpose: - Receives push notifications from Firebase - Displays notifications in system tray - Handles notification clicks to open the app

How it works: 1. Backend sends FCM notification 2. Firebase delivers to device 3. Service receives message 4. Creates and displays notification

Components

UserManager

Location: UserManager.kt

Responsible for: - Initializing anonymous users - Managing FCM tokens - Updating user locations - (Future) Syncing data to backend API

Key Methods: - initializeUser(): Signs in anonymously and saves to Firestore - updateUserLocation(): Gets GPS and updates Firestore

UserRepository

Location: UserRepository.kt

Handles Firebase operations: - signInAnonymously(): Creates anonymous Firebase user - getFcmToken(): Retrieves FCM device token - saveUser(): Saves user data to Firestore - updateUserLocation(): Updates location in Firestore

LocationHelper

Location: LocationHelper.kt

Manages location services: - hasLocationPermissions(): Checks if permissions granted - getCurrentLocation(): Gets precise GPS coordinates - getLastKnownLocation(): Gets cached location (faster)

Data Models

User Model - User.kt:

data class User(
    val uid: String = "",
    val fcmToken: String = "",
    val location: GeoPoint? = null,
    val createdAt: Long = System.currentTimeMillis(),
    val lastActive: Long = System.currentTimeMillis()
)

User Flow

First App Launch

  1. App Opens → MainActivity.onCreate()
  2. UserManager Initialized → Creates UserManager instance

  3. initializeUser() Called: 

    // Step 1: Anonymous sign in
val uid = userRepository.signInAnonymously() // e.g., "abc123def456"

// Step 2: Get FCM token
val fcmToken = userRepository.getFcmToken() // e.g., "fcm_device_token_..."

// Step 3: Save to Firestore
userRepository.saveUser(uid, fcmToken)

  4. Permissions Requested → Location and notifications

  5. Location Updated (if granted): 
    val location = locationHelper.getCurrentLocation()
userRepository.updateUserLocation(uid, location)

Subsequent App Launches

  1. App Opens
  2. Existing User Check → Firebase recognizes returning user
  3. Same UID Used → No new user created
  4. FCM Token Verified → Updated if changed
  5. Location Updated → Fresh GPS coordinates

Firebase Console Verification

Authentication

  1. Go to Firebase Console
  2. Select "bhandara" project
  3. Navigate to Authentication → Users
  4. See anonymous users with UID

Firestore Database

  1. In Firebase Console
  2. Navigate to Firestore Database
  3. Open users collection
  4. View documents with structure: 
    users/
  {uid}/
    - uid: "abc123def456"
    - fcmToken: "fcm_token_..."
    - location: GeoPoint(18.5823749, 73.8844745)
    - createdAt: 1704045600000
    - lastActive: 1704045600000

Cloud Messaging

  1. In Firebase Console
  2. Navigate to Cloud Messaging
  3. View registered FCM tokens
  4. Test notifications from console

Debugging

LogCat Tags

Monitor these tags in Android Studio Logcat:

  • UserManager: User initialization flow
  • UserRepository: Firebase operations
  • LocationHelper: Location updates
  • BhandaraMessaging: Notification handling

Expected Log Sequence

UserManager: User signed in with UID: abc123def456
UserManager: FCM token obtained
UserRepository: User data saved successfully
UserManager: User saved to Firestore
LocationHelper: Location obtained: 18.5823749, 73.8844745
UserRepository: User location updated
UserManager: User location updated in Firestore

Common Issues

Location Not Updating

Problem: Location stays null in Firestore

Solutions: - Check permissions granted - Ensure emulator has location set (Extended Controls → Location) - Use device with GPS instead of emulator - Check Play Services installed on emulator

FCM Token Not Generated

Problem: fcmToken is empty

Solutions: - Use emulator with Google Play (not just Google APIs) - Check google-services.json is valid - Verify internet connection - Restart app

Anonymous User Not Created

Problem: UID is null

Solutions: - Check Firebase Authentication is enabled - Verify google-services.json configuration - Enable Anonymous sign-in in Firebase Console

Security Considerations

Anonymous Auth Limitations

  • Device-specific: UID tied to app installation
  • Non-recoverable: Uninstall = new user
  • No cross-device: Can't sync across devices

Privacy

  • No personal information collected
  • Only: UID, FCM token, location
  • Users can't be identified
  • Complies with anonymous usage

Data Retention

Consider implementing: - Remove users inactive for 90+ days - Clear location data older than 30 days - GDPR compliance for EU users

Next Steps

See Backend Integration for: - Syncing user data to PostgreSQL/PostGIS - Implementing backend API calls - Querying nearby users - Sending targeted notifications