Android Chat App & Backend

*Core Features
1. Real-Time Messaging
One-to-one real-time chat
Built using Node.js + Socket.io (or equivalent real-time engine)
Messages should be delivered instantly when the receiver is online

2. Offline Message Delivery
If the receiver’s mobile is offline / switched off / no internet, messages must be:
Stored securely
Automatically delivered when the user comes online (like WhatsApp)

3. Media & Attachments
Send and receive:
Text messages
Images
PDF files
Chat window should:
Auto-download attachments
Show inline preview for images and PDFs (similar to WhatsApp)

4. Backend Message Sending (PHP API)
Ability to send text and PDF messages from backend
PHP-based API for:
Sending messages
Sending attachments
Useful for system notifications or admin-triggered messages

5. Contact List & Chat UI
Contact list should display:
Contact name (if saved)
Otherwise, mobile number (like WhatsApp)

Show:
Unread message count per contact
New message indicators
Read / unread status handling

6. Notifications
Push notifications for new messages
Notification count per contact and globally
Works reliably when app is in background

7. Message Storage Strategy
Mobile app must:
Store previous messages, images, and PDFs locally
Old messages do not need to remain on the server once delivered and synced
Server storage should be minimal and optimized

*Technical Requirements
Real-time engine: Node.js + Socket.io
Backend API: PHP (for sending messages from server/admin panel)
Database: Developer recommendation (MySQL / MongoDB / etc.)
Mobile App: Android (iOS optional – please specify)
Security: Proper authentication & secure file handling

*Deployment & Delivery

Developer must:
Install and configure backend on my VPS
Deploy and test real-time server
Deliver complete mobile application (APK / source code)
Provide basic documentation for setup and APIs

* Preferred Developer Profile
Proven experience in:
Real-time chat systems
Socket.io / WebSockets
Mobile app development
Clean, scalable, and well-documented code