Full Stack Developer at Kualty

At Kualty, I worked on Thr1ft, a unique second-hand marketplace platform with a mission-based shopping experience. The product consisted of three interconnected systems: a mobile application for customers, a PWA for store owners and administrators, and a Shopify integration.

Experience Overview

• Company: Kualty
• Role: Full Stack Developer
• Timeline: October 2022 - December 2023 (1 year 3 months)
• Location: Colombia
• Product: Thr1ft (Mission-based second-hand marketplace)
• Tech Stack: React, React Native, TypeScript, Shopify API, Node.js, PostgreSQL

About the Product - Thr1ft

Thr1ft was a second-hand marketplace with a unique twist: mission-based shopping. Unlike traditional e-commerce, the platform operated on a time-based system where shopping missions started on specific days (typically weekends), and the app was only open during these mission windows.

The Three-Part System

1. Mobile Application (React Native)

• Customer-facing app for purchasing second-hand products
• One stock per product - First user to purchase wins
• Mission-based access - App only opens during active missions
• Real-time inventory updates to show product availability
• Fast checkout process optimized for competition-style shopping

2. Progressive Web App (PWA)

• Admin and store owner dashboard
• Product management and inventory control
• Mission scheduling and control panel
• Customer management and support tools
• Order review and fulfillment tracking
• Analytics and reporting

3. Shopify Integration

• Connected Shopify stores to Thr1ft platform
• Automated product sync from Shopify → PWA → Mobile app
• Order management across platforms
• Inventory synchronization
• Unified dashboard for Shopify merchants

Key Responsibilities

Mobile App Development

• Built React Native application for iOS and Android
• Implemented real-time product availability system (critical for one-stock items)
• Created mission timer UI showing when next mission starts
• Developed fast checkout flow to handle high-demand purchasing
• Optimized for speed - milliseconds mattered when competing for products
• Implemented push notifications for mission starts and product alerts

PWA Admin Panel

• Developed responsive admin dashboard using React
• Built mission control system for scheduling and managing shopping windows
• Created product management interface with bulk upload capabilities
• Implemented order management and customer support tools
• Built analytics dashboard for tracking mission performance
• Designed role-based access control for different admin levels

Shopify Integration

• Integrated Shopify API for product synchronization
• Built middleware to transform Shopify products for Thr1ft format
• Implemented webhook handlers for real-time inventory updates
• Created OAuth flow for merchant onboarding
• Developed sync engine to handle product updates and conflicts
• Built admin interface for managing connected Shopify stores

Mission-Based System

• Designed and implemented time-gated access system
• Built scheduling engine for mission start/end times
• Created countdown timers and real-time status updates
• Implemented queue system for high-traffic mission starts
• Optimized database queries for concurrent user access during missions

Key Challenges & Solutions

Challenge 1: Race Conditions on Single-Stock Items

Problem: Multiple users attempting to purchase the same item simultaneously (only 1 stock available).

Solution:

• Implemented optimistic locking at database level
• Added transaction handling with rollback on conflicts
• Created real-time inventory updates via WebSockets
• Built UI feedback for "item no longer available" scenarios
• Implemented cart expiration (15-second hold) to prevent abandoned carts blocking inventory

Challenge 2: High Traffic During Mission Starts

Problem: Hundreds of users accessing the app simultaneously when missions opened, causing server strain.

Solution:

• Implemented queue system for mission entry
• Used Redis for session management and caching
• Optimized database queries with proper indexing
• Added CDN for static assets
• Implemented progressive loading for product lists
• Created load testing scenarios to prepare for peak traffic

Challenge 3: Shopify Sync Reliability

Problem: Ensuring Shopify inventory stayed in sync with Thr1ft without conflicts or delays.

Solution:

• Built webhook retry mechanism with exponential backoff
• Implemented conflict resolution rules (Shopify as source of truth)
• Created sync status dashboard for merchants
• Added manual sync trigger for troubleshooting
• Logged all sync operations for debugging

Challenge 4: Time Zone Management

Problem: Missions needed to start at correct local times for different regions.

Solution:

• Stored all times in UTC, converted on client
• Added timezone configuration per mission
• Built preview system to verify mission times
• Created automated tests for timezone edge cases

Skills Developed

Technical Skills:

• React Native mobile development
• Progressive Web App architecture
• Shopify API integration and OAuth
• Real-time systems with WebSockets
• Race condition handling and optimistic locking
• High-traffic system optimization

E-commerce Domain:

• Inventory management systems
• Payment processing and checkout flows
• Mission/time-based product releases
• Multi-tenant architecture (Shopify merchants)

Soft Skills:

• Working under time pressure (fast-paced product launches)
• Cross-functional collaboration with product and design teams
• Problem-solving for unique business models
• Debugging production issues in real-time during missions

Impact & Results

Performance Metrics

• Mobile App: Smooth performance during high-traffic missions (500+ concurrent users)
• PWA: Fast admin operations with sub-second response times
• Shopify Sync: 99.8% sync success rate with automatic retry on failures

User Experience Wins

• Fast checkout: Average purchase time under 10 seconds
• Real-time updates: Inventory changes reflected instantly
• Mission reliability: Missions started on time with queue system handling traffic spikes
• Cross-platform sync: Shopify → Thr1ft sync completed within 2 minutes

Technical Highlights

Architecture:

• Monorepo structure with shared TypeScript types
• REST API with WebSocket support for real-time features
• PostgreSQL with optimistic locking for inventory
• Redis for caching and session management
• Queue system (Bull) for background jobs

Mission System:

• Cron-based scheduler for mission activation
• State machine for mission lifecycle (upcoming → active → ended)
• Real-time countdown synchronized across all clients
• Grace period handling for late checkouts

Shopify Integration:

• OAuth 2.0 for merchant authentication
• Webhook subscriptions for real-time updates
• Bulk import API for initial product sync
• Rate limiting compliance with Shopify API

This role taught me how to build systems that handle time-critical operations, manage race conditions in high-traffic scenarios, and integrate with third-party platforms like Shopify.

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Key Takeaway: Working on Thr1ft taught me how to build time-gated, high-competition e-commerce systems where performance and reliability are critical to the user experience.