🤔 Product Requirements

1. Calculate VAT taxes in Cirrus ERP/HIS
   • Initially: 🇲🇽Mexico, 🇸🇦Saudi Arabia, 🇦🇷Argentina
   • Integrate with current Tax implementation for 🇲🇽MX
2. Configurable rules: Exotic tax regulation often changing
   • Ex. Monthly in ARG, due to currency inflation

📐Constraints

• Easy enough for non-programmers (a.k.a. Accountants) to use
• Existing technical debt in financial module of big/old Java monolith
• Time sensitive: Tax season in MX in <3 months

As-is Architecture

🚧 Revised Tech Specs

1. Arch: SOA/Bounded-Context => Microservice/ Lambda
2. Simple DSL JSON-based configuration
3. In-memory/Hardcoded data store for config​ 
4. Memoization
5. TDD/BDD for fast iteration

🚫 Non-goals (for MVP)

1. Avoid refactoring Java module, stick to HTTP interface
2. Configurable interface/UI (*PoC)
3. Full blown DB
4. No cache
5. No pre-defined rules format

To-be Architecture

🛠Technical Dive

• Zeit Micro framework / monorepo
  • Flexibility between MS or ƛs
• LowDB: NoSQL-like lightweight ORM
• Jest: For Unit Testing
  • Test cases directly from PO/Accountants
  • Normalized Excel-like rules
• CI/CD server for continuous adjustements
• Don't re-invent the wheel:
  • Currency.js: Decimals & rounding
  • hot-formula-parser: Excel-like formulas
  • moment.js: Dealing with Time(zones)
  • Standard.js: Syntax not worth discussing
  • lodash: For everything else

Thanks!

github.com/benoror/taxi-driver

Lessons learned

• Out-of-the-box thinking is great way to move forward both culturally and technically
• Working under constraints is always good to get the best out of your team.
• There's always fun and interesting ways to make legacy and newer tech work together.
• It's all about empowering people, not the technology itself.