Sergi is available for hire
Hire SergiSergi Wojtowicz
Verified Expert in Engineering
Software Developer
Location
Warsaw, Poland
Toptal Member Since
December 2, 2019
Sergi is a software developer with over 15 years of professional programming experience. Over the years, he's worked with a wide range of technologies creating web, mobile, and desktop applications and gaining extensive experience with relational databases, including big data. Recently, Sergi has been fascinated by the next generation of programming languages—namely Kotlin and TypeScript—which he uses to create single-page applications.
Portfolio
Daventry Solutions, LLC (via Toptal)
REST, JSON, Imperative Programming, HTML, Data Analysis...
GenesisMobo Sp. z o.o
Node.js, Linux, Microservices Architecture, Microservices, REST...
Mobo Studio
JSON, Software Design Patterns, Redmine, Subversion (SVN), MacOS...
Experience
Availability
Part-time
Preferred Environment
Linux, GitLab, IntelliJ IDEA, Sublime Text, Ubuntu
The most amazing...
...project I've participated in was a technology-independent environment that provides a unified web application interface.
Work Experience
JavaScript Expert
2020 - 2020
Daventry Solutions, LLC (via Toptal)
- Developed a JSON document definition format including a logical language to evaluate score and exclude sections or fields, implemented a generic component that creates views based on definitions and allows one to enter or retrieve values.
- Implemented ElasticSearch API capable to work with over 10,000 results and refactored application to use the API, which included both the frontend as well as the synchronization and computation process.
- Implemented search logic language (OR, AND, NOT) with auto-completion and suggestions on frontend side, search queries are translated into SQL and ElasticSearch queries.
- Implemented various views, calculations, formulas, and UI improvements and fixed bugs.
Technologies: REST, JSON, Imperative Programming, HTML, Data Analysis, Object-oriented Programming (OOP), Web Applications, Full-stack, Git, CSS, Algorithms, SQL, Elasticsearch, SQLite, Bootstrap, Express.js, Node.js, Nuxt.js, Vuex, Vue, TypeScript, JavaScript
IT Director | Co-founder
2013 - 2020
GenesisMobo Sp. z o.o
- Managed various projects (typically two to four in a year) in teams of two to five employees. Served as a senior developer on several projects using various technologies.
- Designed a multi-modular architecture in which each module has a separate GIT code repository and can, therefore, be developed separately. The implementation was based on PHP (CodeIgniter), JavaScript (AngularJS), Less (CSS), and npm.
- Managed the implementation of the application used to organize the traffic of over 1,000 city buses in real-time. I was responsible for creating the skeleton of a multi-module application based on CodeIgniter, jQuery (JavaScript), and PostgreSQL.
- Created many complex and optimal queries for the PostgreSQL database using the WITH clause to prepare data for the final query, as well as LAG and LEAD window functions.
- Created an authorization engine for web applications based on session cookies and JWT in Ktor (Kotlin) together with an npm library written in Angular (TypeScript), which refreshes the token in the background every two minutes.
- Built an application designed to report the number of passengers in vehicles presenting data both in tabular form, on charts, and on a map. The application is based on Ktor (Kotlin), Angular (TypeScript), and the PostgreSQL database.
Technologies: Node.js, Linux, Microservices Architecture, Microservices, REST, JSON Web Tokens (JWT), Ktor, Leaflet, Angular Material, JSON, Software Design Patterns, Redmine, Imperative Programming, HTML, FTP, OpenStreetMap, CSV, Data Analysis, Object-oriented Programming (OOP), Web Applications, Full-stack, Angular, Chart.js, PostGIS, GitLab, Git, CSS, AngularJS, Algorithms, CodeIgniter, SQL, Qt, JavaScript, PHP, Java, PostgreSQL, Kotlin, TypeScript
Senior Developer | Project Manager | Co-founder
2009 - 2017
Mobo Studio
- Implemented various games and applications for both iOS and Android.
- Constructed a framework for iOS that provided a set of reusable components that was used to quickly implement presentation applications.
- Developed a web application that allows the user to find vehicle or to check the occupancy of parking spaces based on the vehicle's GPS location.
- Implemented parts of a platform built on Android which included among cryptography, an offline mode with data synchronization, registration, and blocking devices.
Technologies: JSON, Software Design Patterns, Redmine, Subversion (SVN), MacOS, Imperative Programming, HTML, FTP, CSV, Data Analysis, Object-oriented Programming (OOP), Web Applications, Full-stack, jQuery, CSS, AngularJS, Algorithms, CodeIgniter, SQL, PostgreSQL, JavaScript, PHP, Objective-C, Java
Senior Java Developer | Project Manager
2006 - 2009
Cyberware Poland
- Built a platform-independent framework that was used for CRM/ERP implementations and consists of auto-updates and support for CRUD based on XML form definition among other things.
- Created a solution for digital newspapers. It consists of a Java desktop application where one could map areas of a PDF with content recognition to create ready-to-read articles and websites.
- Extended or redefined with the help of Reflection, Java, AWT, and Swing components to implement a modern UX/UI (which was created by a designer on the project).
Technologies: Software Design Patterns, Imperative Programming, Data Analysis, Object-oriented Programming (OOP), SQL, JavaScript, PostgreSQL, PHP, Java
Web Developer
2004 - 2006
Creaciones Virtuales
- Implemented an MVC framework in PHP used by all of the company employees for development.
- Created various websites and web applications for the public administration of Spanish provinces.
- Invented, designed, and implemented a task-based system to replace assigning programming tasks in verbally or on paper.
- Implemented a tool that was a Gantt financial chart used to plan the finances of provincial projects.
- Established object-oriented programming in PHP, which has been appreciated and has become the company's standard.
Technologies: Software Design Patterns, Imperative Programming, HTML, Object-oriented Programming (OOP), Web Applications, Full-stack, CSS, SQL, Flash, PostgreSQL, MySQL, JavaScript, PHP
Web Developer
2002 - 2004
Freelance Work
- Created a reusable CMS in PHP with authorization and content management.
- Implemented support for the CMS into Flash for interactive websites.
- Developed various websites for Polish companies and organizations based on a reusable CMS.
Technologies: Imperative Programming, HTML, Object-oriented Programming (OOP), Full-stack, CSS, SQL, Flash, MySQL, PHP
Experience
Bus Traffic Management System
I managed the implementation of the bus traffic management system while participating in it as a senior developer.
The system is used every day during the organization of traffic of over a thousand buses using, among others, functions such as punctuality control, alarms in the event of irregularities, registration of communication events and vehicle failures. The system fully integrates with the solutions owned by the client, downloading the data it needs and providing data for other systems.
The system is used every day during the organization of traffic of over a thousand buses using, among others, functions such as punctuality control, alarms in the event of irregularities, registration of communication events and vehicle failures. The system fully integrates with the solutions owned by the client, downloading the data it needs and providing data for other systems.
Customer Request System
I built an application designed to handle customer requests for both software and hardware.
The part intended for the customer is completely separated from the part used for handling notifications, also at the database level. The system integrates with the company's data sources. The functionality allows, inter alia, the flow of requests between IT and hardware departments, planning the sending of service technicians, and assessing the quality of service technicians' work.
The part intended for the customer is completely separated from the part used for handling notifications, also at the database level. The system integrates with the company's data sources. The functionality allows, inter alia, the flow of requests between IT and hardware departments, planning the sending of service technicians, and assessing the quality of service technicians' work.
Colorix Game
https://www.youtube.com/watch?v=cs5qC5fCAOg&t=83sI implemented Colorix, a game for Android and then also helped with implementation for iOS.
Colorix is a match 3 puzzle game similar to Tetris. The game offers beautiful graphics that have been appreciated by critics. Both the Android and iOS versions were high in their category at one time. In addition, Apple chose the game as worth checking out and promoted it by placing it on the main page of its store for a week.
Colorix is a match 3 puzzle game similar to Tetris. The game offers beautiful graphics that have been appreciated by critics. Both the Android and iOS versions were high in their category at one time. In addition, Apple chose the game as worth checking out and promoted it by placing it on the main page of its store for a week.
Skills
Languages
PHP, JavaScript, TypeScript, SQL, Objective-C, Kotlin, Java, HTML, CSS
Frameworks
CodeIgniter, Angular, AngularJS, Nuxt.js, Express.js, Bootstrap, Qt, Ktor, Angular Material, JSON Web Tokens (JWT)
Other
Full-stack, Web Applications, CSV, OpenStreetMap, FTP, Algorithms, Data Analysis
Libraries/APIs
jQuery, Vue, Vuex, Node.js, Leaflet, Chart.js
Paradigms
REST, Microservices, Microservices Architecture, Object-oriented Programming (OOP), Imperative Programming
Storage
PostgreSQL, Elasticsearch, SQLite, JSON, PostGIS, MySQL
Tools
Sublime Text, IntelliJ IDEA, Flash, Git, GitLab, Subversion (SVN), Redmine
Platforms
Linux, Ubuntu, Software Design Patterns, MacOS
Education
2000 - 2004
Bachelor's Degree in Computer Engineering
University of Warsaw - Warsaw, Poland
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