docs: [FEATURE] Create ARCHITECTURE.md documentation #194

Author: rohitkumarnaidu

ARCHITECTURE.md

@@ -0,0 +1,76 @@
+# Aarini Architecture
+
+Aarini is a cross-platform mobile application built to provide health insights, cycle tracking, and ML-powered predictions. The system is split between a React Native (Expo) frontend and a Python-based backend handling the predictive logic, all bound together by Firebase for real-time data synchronization.
+
+## ?? High-Level Overview
+
+The architecture is divided into three primary tiers:
+
+1. **Client / Frontend (`frontend/`)**: An Expo React Native application providing the user interface, state management, and device integration.
+2. **Backend API (`backend/`)**: A Python-based service responsible for machine learning algorithms, cycle predictions, and data analysis.
+3. **Database & Auth (Firebase)**: Firestore provides real-time NoSQL data storage (governed by `firestore.rules`), while Firebase Authentication secures user sessions.
+
+### ?? System Architecture Diagram
+
+```mermaid
+graph TD
+    User[End User (Mobile)]
+    
+    subgraph Frontend Application
+        Expo[React Native / Expo App]
+        Context[React Context / State]
+        Screens[UI Screens & Components]
+        Services[API Services / Hooks]
+    end
+    
+    subgraph Backend Services
+        Python[Python API]
+        ML[Cycle Prediction Engine]
+    end
+    
+    subgraph Firebase Infrastructure
+        Auth[Firebase Authentication]
+        Firestore[Cloud Firestore DB]
+    end
+    
+    User -->|Interacts| Screens
+    Screens -->|Dispatches| Context
+    Context -->|Uses| Services
+    
+    Services -->|Authenticates| Auth
+    Services -->|Reads/Writes| Firestore
+    Services -->|Fetches Predictions| Python
+    
+    Python -->|Queries History| Firestore
+    Python -->|Runs Models| ML
+```
+
+## ?? Directory Structure
+
+### Frontend (`frontend/`)
+- **`assets/`**: Static images and fonts.
+- **`components/`**: Reusable UI components.
+- **`screens/`**: Full-page views for navigation.
+- **`context/`**: Global state management (Auth, Theme).
+- **`services/`**: API wrappers and Firebase interactions.
+- **`utils/`**: Helper functions and parsers.
+- **`navigation/`**: React Navigation configurations.
+
+### Backend (`backend/`)
+- **`app.py`**: Main application entry point for the REST API.
+- **`cycle_prediction.py`**: Core algorithm for predicting cycles.
+- **`tests/`**: Unit tests for backend logic.
+
+## ?? Data Flow
+
+1. **User Input**: A user logs a new symptom on the mobile app.
+2. **Frontend Service**: The `frontend/services` layer packages this data and sends it securely to Firebase Firestore.
+3. **Backend Trigger**: When the user requests a new prediction, the Python backend queries the recent data from Firestore.
+4. **Processing**: `cycle_prediction.py` processes the historical data.
+5. **Response**: The backend returns the predicted dates to the frontend, which updates the React Context and re-renders the UI.
+
+## ?? Deployment Strategy
+
+- **Frontend**: Distributed via Expo Application Services (EAS).
+- **Backend**: Containerized/Deployed via standard PaaS providers (e.g. Render, Vercel, Heroku) as defined by `render.yaml`.
+- **Database**: Serverless deployment on Google Cloud via Firebase.