PaymentSystem

Used Technologies

Grape For fast and well designed API
Swagger for interactive API documentation
Grape::Entity for api presenters
Ruby (2.5.8)
RSpec For Unit & API Tests
Capybara For UI tests
Best CSV tool ever - SmarterCSV
Custom ideally horizontal scaling API authentication based on JWT JWT
Pry For Easy Debugging And Code Inspecting
Sidekiq for background jobs, sidekiq-scheduler for scheduling
Draper for views wrappers
Rails 5.2.4.3 - this version was released at May 18, 2020, Rails 6 was incopable with some technologies that are using here
Devise for simple UI authentication
state_machine for different transaction types statuses
Bootstrap

Service Objects - based on Command (for authentication) & Strategy for user input processing
Convention Over Configuration principle used for complex user params processing at API
Form Objects - used together with service objects - they encapsulates validation logic to make new Transactions approved, or move them to error state (Context pattern with service strategy)
Special State Machine for each transaction type - for more flexibility
Presenters - including special presenter for form result
Wrappers (Draper's decorators)
MySQL Enum instead of rails enum
Foreign Keys for dependent tables
STI for Transactions
CSV import works using also Service Objects & Form Objects
Optimistic locks for merchants & transactions to prevent double changes

System support 4 different types of transactions
Transactions can be dependent to each other
Transactions should be created and moved to status 'error' when they are partially invalid, so we cannot use plain rails validations practice, and should have validations at forms & models
Merchants can moved to inactive status - so system will not create new transactions for such merchants
To remove merchant - merchant should have 0 transactions, that can be done after removing transactions by schedule
User will be able to upload csv with different fields in different order, but some of them are required
Removing Job runs by schedule every hour, and remove all transactions that related to authorize transactions that were created more than one hour ago, this is needed to have referential integrity
System has different UI's for admins and merchants
System has seeds for basic data

Tests Coverage 98% by SimpleCov, including browser tests, api tests, and unit tests for services
Code Inspected by RuboCop, no offenses detected
Code Inspected for security vulnerabilities by Brakeman, no warnings found