Kamil Leszczuk

Experience

1. Vertex (Taxamo) 2020 - current

   I started working at Taxamo as a software engineer, building a complex tax caclulation and invoicing system. Over time my responsibilities expanded, and eventually I took on a role of a team leader. I was also largely involved in system architecture and user inteface design.

   Most of the software development I did was in Clojure and ClojureScript, with our apps deployed to AWS and using several cloud services, like DynamoDB. I've also implemented smaller subsystems in modern web technologies like htmx.

   As a team lead, I've been responsible for the work of a 6-8 people strong team, learning how to empower them to do their best work.

   Being a senior engineer on the project, I designed and led implementation of multiple major functionalities. A few examples:

   • a future-proof invoicing solution supporting 20+ languages and 100+ countries, extensible using a layered rule system
   • a new generation of reprorting solution, utilising Snowflake, Athena, Flink, Debezium
   • a redesign of the user interface (React.js, Reagent)
   • an auditable, immutable customer profile database based on the even sourcing pattern
2. Raiffeisen Bank International 2022 - 2023

   I've helped to build a bank loan management system. It was an event sourcing system built using a microservices architecture. It was deployed to AWS and was using a Gerrit review system.

   Specifically I was working on a subsystem responsible for handling, calculating and aggregating multi-dimensional data efficiently. It had to satisfy auditability and security requirements associated with a practices of a major banking institution.

3. Aviso (Fexco) 2014 - 2020

   I was working with Aviso (a FEXCO company) on several products.

   One was a payment switch, where my focus was on the frontend (Angular.js, later React.js) and the associated REST services (including database layer). Eventually I became a lead developer of the frontend part of the system.

   Later, I've worked on a payment solution for the hospitality market. There I've developeed two web applications: a customer facing one (Vue.js) and an internal one (ReasonML, React.js). Both were backed by backends running on GCP, one with Spanner as a primary database, the other - Datomic.

   Work at Aviso was the first time I was professionally working in Clojure and ClojureScript. That has defined the next 10+ years of my career as an engineer most familiar with JVM / Clojure and frontends.

4. Deutsche Telekom 2014 - 2015

   Working at DT, I was cooperating closely with the Mozilla team on Firefox OS. The focus was on building up a support for NFC in Mozilla's new mobile operating system. Therefore I've spent this year creating NFC payments capabilitis, as well as other, secondary functions (like contact sharing).

   This was at a time the biggest engineering project I've been involved with, and I learned a lot about such aspect of software engineering like processing code changes to meet not only functional, but also architectural and security standards, as well as about good practices on organising the work of highly distributed, remote teams.

5. Piękna Spa 2014 - 2024

   This small side project for my wife's business was a nice opportunity to try out and learn new things. I've happily overengineered it and designed a website and, from scratch, an online store for digital gift cards. It was a fully fledged store, with an admin panel, PDF invoicing module, email sending capabilities etc.

   Frontend part was well optimised, with perfect Lighthouse scores. To a point where some (non-techincal) customers were mentioning to my wife that their website loads very fast.

   Backend was written in Go and deployed to AppEngine.

6. T-Mobile 2010 - 2014

   Work at the Innovation Team was very interesting and fun at the same time. We’ve had mandate to prototype and validate new ideas quickly.

   This has led me on a journey where I’ve been implementing both production ready REST APIs in Java allowing customers to tap into the y networking infrastructure, and then rapidly change gears and prototype in C++ a network of embedded systems. And all the things in between.

   I’ve learned a ton and consider this a great start into my career.

7. Prior to that I worked as a packet core specialist for T-Mobile (2009-2010); software developer for Orange (2008); translator for Polimex-Mostostal (2007, summer job); frontend developer for Siedlce City Museum and Cultural Center (2004-2005, high school job).