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FitIn is an innovative mobile fitness application that leverages advanced AI architecture to deliver personalized coaching experiences. I conceived and deployed a RAG (Retrieval-Augmented Generation) system architecture, integrating a Large Language Model (LLM) with a vector database stored on Supabase (PostgreSQL) to ensure relevant, context-aware workout sessions based on a comprehensive knowledge base. This approach reduced AI hallucination rates by approximately 30% and improved workout plan relevance by 15% (measured by user completion rates). The application is built on a full Serverless architecture using Supabase Edge Functions for API request handling and critical business logic, enabling horizontal scalability for training sessions while optimizing infrastructure costs. This Serverless approach reduced backend hosting costs by approximately 40% compared to traditional VM architecture while handling traffic spikes without latency issues. I developed a complete Freemium monetization model with a Coach Points system for unlocking premium services, integrating AdMob for banner and Rewarded Video Ads, and Stripe for premium subscription payments. This monetization strategy increased potential revenue per free user by approximately 25% through the points reward system and ensured smooth Ad-Free conversion to paid subscriptions. As a Full Stack Developer/Architect, I managed the entire project lifecycle from data model design to detailed UI implementation, achieving successful publication on both Apple App Store and Google Play Store.

Period

May 2025 - Present

Role

Full Stack Developer / Architect (React Native)

Team

Me as developer and 3 founders

Work Mode

Remote - Freelance

Key Achievements

  • Successfully published and managed the application on both Apple App Store and Google Play Store, automating the entire release lifecycle using Expo EAS and Expo Platform APIs for continuous delivery
  • Conceived and deployed RAG (Retrieval-Augmented Generation) architecture with vector database on Supabase (PostgreSQL), reducing AI hallucination rates by approximately 30% and improving workout plan relevance by 15% (measured by user completion rates)
  • Implemented full Serverless architecture using Supabase Edge Functions for API requests and business logic, achieving 40% reduction in backend hosting costs vs traditional VM architecture while handling traffic spikes without latency
  • Developed complete Freemium monetization model with Coach Points system, AdMob integration (banners + rewarded video ads), and Stripe payment gateway, increasing potential revenue per free user by approximately 25%
  • Designed and delivered monetizable MVP as Full Stack Developer/Architect, managing entire project lifecycle from data model (Supabase) design to detailed UI implementation
  • Built cross-platform mobile application supporting both Android and iOS with native performance and seamless user experience
  • Integrated OpenAI API with RAG system for intelligent, context-aware workout plan generation and personalized coaching conversations
  • Implemented Text-to-Speech (TTS) functionality for voice-guided workout instructions and real-time coaching feedback
  • Integrated WebRTC for real-time video coaching sessions and live trainer interactions
  • Developed modular, reusable components with dynamic theming (light/dark mode) and responsive UI
  • Created personalized workout plan generation system based on user profile, goals, fitness level, and semantic search results
  • Implemented exercise demonstration system with GIF animations and detailed instructions
  • Built progress tracking and workout history features with data visualization and analytics
  • Designed and implemented premium subscription management system with user segmentation and business logic
  • Ensured clean architecture, separation of concerns, and atomic design principles for maintainability and scalability

Responsibilities

  • End-to-end mobile application development and architecture design (data model, development, testing, deployment)
  • Full management of App Store and Google Play Store publication processes using Expo EAS and Expo APIs to automate builds, submissions, and release management
  • RAG system architecture design and implementation with vector database (PostgreSQL/Supabase) for semantic search
  • Serverless/Edge Functions development and optimization using Supabase Edge Functions for scalable API handling
  • Monetization logic development including Freemium model, Coach Points system, AdMob integration, and Stripe payment gateway
  • Business logic implementation for user segmentation, premium feature access, and subscription management
  • AI integration with LLM and prompt engineering for personalized workout recommendations using RAG architecture
  • TTS implementation for voice-guided coaching experience
  • WebRTC integration for real-time video coaching features
  • Cross-platform development for Android and iOS
  • Backend integration with Supabase for authentication, vector database, and real-time data management
  • UI/UX design implementation with responsive layouts
  • Performance optimization for smooth mobile experience and cost efficiency
  • Version control and task breakdown using Git + GitHub
  • Component estimation and delivery planning in collaboration with stakeholders

Technologies Used

React Native 0.82Expo SDK 54TypeScriptRAG System ArchitectureVector Database (PostgreSQL/Supabase)Semantic SearchServerless Functions (Edge/Supabase Functions)Supabase Edge FunctionsSupabase (Auth, Database, Storage, Realtime)OpenAI API (ChatGPT)LLM IntegrationAdMob (Rewarded Video Ads)Stripe Payment GatewayFreemium Model ImplementationWebRTCText-to-Speech (TTS)React Native VoiceReact Native WebRTCiOS DevelopmentAndroid DevelopmentGitGitHubFigmaExpo GoEAS BuildEAS SubmitExpo Platform APIsApp Store ConnectGoogle Play Console

Key Statistics & Impact

2
Platforms Supported
Android & iOS
30% reduction
RAG Architecture Impact
AI hallucination rate decrease
40% reduction
Serverless Cost Savings
Infrastructure cost savings
25% increase
Monetization Impact
Revenue per free user
PostgreSQL/Supabase
Vector Database
Semantic search engine
RAG + OpenAI
AI Integration
LLM with vector database
WebRTC
Real-time Features
Video coaching sessions

Key Features & Modules

RAG-Powered Personalized Workout Plans
Vector Database & Semantic Search
Serverless Edge Functions Architecture
Automated Store Deployment (Expo EAS)
Freemium Model (Free/Premium Tiers)
Rewarded Video Ads (AdMob)
Coach Points System
Stripe Payment Integration
Premium Subscription Management
Text-to-Speech (TTS) Voice Guidance
WebRTC Real-time Video Coaching
Cross-platform Support (Android & iOS)
Exercise Demonstrations with GIFs
Progress Tracking & Analytics
Workout History & Statistics
User Profile & Goal Management
Real-time Chat with AI Coach
Dark/Light Mode Theming
Offline Workout Support

Methodology

Agile - Feature-driven development

Work Mode

Remote - Freelance

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FitIn — Freelance - HealthTech / Coaching · Lamjed Gaidi — Portfolio