ProCode

Project Overview

ProCode is a calculation-driven mobile application where users can perform industry-standard electrical calculations, read technical articles, bookmark content, and securely store calculation results. The app follows a freemium model, allowing limited free usage before requiring an in-app subscription.

The backend was built with scalability, accuracy, and security in mind, supporting mobile apps and an admin dashboard developed by separate team members.

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Key Features & Responsibilities

🔹 Advanced Electrical Calculation Engine

• Implemented NEC-compliant calculation logic including demand factors, conductor ampacity, adjustment factors, voltage drop calculations, grounding conductor sizing, box fill calculations, and resistivity-based formulas.

• Designed the system to handle complex rule-based calculations using structured tables and reusable utility functions.

• Ensured calculation accuracy and consistency across all user inputs and scenarios.

🔹 Subscription & Premium Access System

• Designed a subscription tracking system integrated with App Store and Play Store in-app purchases.

• Implemented backend logic to track premium status, subscription expiry, and access control.

• Limited free users to 5 free calculations, enforcing premium access afterward.

• Ensured premium validation is server-side to prevent client-side manipulation.

🔹 Article & Knowledge Management

• Built a full article management system where admins can create, edit, delete, and manage technical articles.

• Enabled users to read, bookmark, and save articles securely using database persistence (not local storage).

• Designed role-based access control to separate admin and user capabilities.

🔹 Saved Calculations & User Data Persistence

• Implemented database-driven storage for saved calculation results, allowing users to revisit historical data.

• Designed relational data models using Prisma to ensure clean and efficient data relationships.

• Ensured saved data is linked securely to authenticated users.

🔹 Background Jobs & Email Automation

• Integrated BullMQ with Redis for background processing.

• Implemented scheduled cron jobs for:

  • Email notifications

  • Subscription status updates

  • System maintenance tasks

• Designed the system to handle background jobs reliably without blocking the main API.

🔹 Authentication & Security

• Implemented JWT-based authentication with secure cookie handling.

• Added password hashing using bcrypt and request validation using Zod.

• Ensured protected routes for premium features and admin functionality.

🔹 DevOps & Deployment Ownership

• Fully managed DevOps responsibilities for the backend server.

• Deployed the application on a VPS environment using Docker.

• Configured Nginx as a reverse proxy, including API routing.

• Set up SSL certificates for secure HTTPS communication.

• Managed environment variables, production builds, and server monitoring.

• Handled image uploads by storing files directly on the VPS and serving them via public URLs (no AWS S3 used).

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🔹 Challenges & Solutions

🔴 Challenge 1: Implementing Accurate NEC-Based Electrical Calculations

Problem:
Electrical calculations follow strict NEC rules with multiple conditional tables, adjustments, and dependencies, making them error-prone if not structured correctly.

Solution:

• Converted NEC tables into structured TypeScript objects.

• Built reusable utility functions for demand factors, ampacity adjustment, voltage drop, and grounding logic.

• Centralized all calculation logic to ensure consistency and testability.
  This ensured industry-grade accuracy and long-term maintainability.

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🔴 Challenge 2: Subscription Validation with In-App Purchases

Problem:
In-app purchases are processed by App Store and Play Store, requiring secure server-side validation and expiry tracking.

Solution:

• Designed a subscription schema to store purchase status, expiry date, and premium flags.

• Synced app purchase data with backend records.

• Enforced premium access checks at API level instead of client side.
  This prevented unauthorized access and ensured fair monetization.

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🔴 Challenge 3: Background Jobs Without Affecting API Performance

Problem:
Email sending and cron jobs could slow down the API if handled synchronously.

Solution:

• Integrated BullMQ with Redis for background processing.

• Offloaded heavy tasks to worker queues.

• Used cron scheduling for recurring jobs.
  This improved API responsiveness and system reliability.

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🔴 Challenge 4: Managing User Data Across Devices

Problem:
Using local storage would not allow users to access saved data across devices.

Solution:

• Stored bookmarks and calculation results in the database.

• Linked saved data with authenticated user accounts.
  This allowed seamless data access across devices and sessions.

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🔴 Challenge 5: Full DevOps Ownership on Production VPS

Problem:
Ensuring security, performance, and reliability without managed cloud services.

Solution:

• Dockerized the backend for consistent deployments.

• Configured Nginx for reverse proxy and SSL termination.

• Secured the server with HTTPS, environment isolation, and proper process management.
  This ensured a stable and production-ready backend environment.

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🔹 Learning Outcomes

• Gained deep experience building rule-based calculation engines.

• Learned how to handle mobile in-app subscription validation securely.

• Improved expertise in background job processing with BullMQ and Redis.

• Strengthened DevOps skills including VPS deployment, Nginx, SSL, and Docker.

• Enhanced ability to collaborate in multi-team architectures (backend, app, dashboard).

🔹 App Links

   App Store: https://apps.apple.com/us/app/procode/id6754005427

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🔹 Technology Stack

Frontend (Handled by Other Team Members)

• Mobile App (iOS & Android)

• Admin Dashboard (Web)

Backend

• Node.js, Express.js

• TypeScript

• Prisma ORM

• PostgreSQL / Database (via Prisma)

• JWT Authentication

• Zod Validation

Background Jobs & Queue

• BullMQ

• Redis

DevOps & Infrastructure

• Docker

• VPS Deployment

• Nginx (Reverse Proxy)

• SSL Certificate Setup

• PM2 / Process Management

Utilities & Tools

• Nodemailer