Spree Commerce VS Active Merchant

A good system to study is Spree https://github.com/spree/spree. It has an inventory and billing system and supports different adjustments and sale configurations. If you don't want to use it wholesale it's a solid Rails application that does most of what you want so you can use it as solid inspiration.

Spree Commerce: https://spreecommerce.org/

Maybe Spree?

I'd say Solidus and Spree are you best options rather than trying to roll out you own ecommerce solution.

When I was working on that company, that mobile ordering app, Counterless, I looked a lot at codebases like Spree, the Spree Commerce codebase. And that's how I learned a lot about how do you model an order with line items and things like that? I saw some amazing things that helped me develop an understanding and save a ton of time by looking at oh, they have a state machine. What are the ways that an order transitions through all these different states as it gets processed and charged? And how do you track all of those things?

For example, their theme templates use Liquid, which is a html templating system for Ruby. Activemerchant also was released by Shopify, and it provides a interface to major payment providers like PayPal.

For ruby there is a nice library from Shopify offering a huge number of payment gateway integrations: https://github.com/activemerchant/active_merchant

Administrate – for building and customizing admin panels; became successful because of its ease for users without a technical background. Money-Rails – for E-commerce solutions; enables creating monetary values, additional entry fields, and money classes. MetaTags – for SEO management, as the name suggests. Draper – for object-oriented programming; helps monitor and improve each object’s behavior. Dotenv – for safe loading environment variables to protect private data. ElasticSearch – to implement searches, to index catalogs and prices, to store purchases, and to gather statistics. Sidekiq – for storing, monitoring, and managing background jobs. Fog – for uploading and storing files via cloud services. Unicorn – for deploying. Active Merchant – for integrating payments.