Eliam Pimentel

The problem

A lottery operator with several points of sale needs to sell and print tickets at each one, control limits, cash and prizes, and see reports from one place, without their data mixing with another operator's. Trébol centralizes that operation and keeps the sensitive rules on the server, not in the app.

What I built

• The NestJS API with Prisma and PostgreSQL: authentication, roles and permissions, tenants, points of sale, lotteries, draws, tickets, sales limits, cash, prizes, reports, notifications and audit logs.
• Ticket sales with an idempotency key in a serializable transaction that is retried on serialization conflicts, so a network retry or two simultaneous sales can't duplicate a ticket or break a limit.
• Scheduled jobs with @nestjs/schedule: daily generation of draw sessions, closing sales when a draw is due, reminders, and ingesting results from a public feed (RSS and JSON-LD) every 5 minutes.
• The Next.js and HeroUI admin panel, in Spanish and English, with a platform area (tenants, catalog, results, audit) and an area for each operator (points of sale, users, roles, limits, tickets, cash, prizes, reports).
• The Expo app for iOS and Android: ticket sales, cash by shift, Face ID unlock, ticket validation with the camera, push notifications and Bluetooth thermal printing.
• Printing: ESC/POS commands sent over BLE in chunks, with the receipt and its QR code rasterized in the app itself.

Architecture

1. Expo app (iOS/Android) and Next.js panel
2. NestJS API (REST)
3. PostgreSQL + Prisma
4. Redis (shared rate limiting)

Challenges and decisions

Results

• Live on the App Store.
• 359 commits in the repository.
• 52 Prisma models and 45 migrations.
• 362 test files with the Node test runner.

Gallery

Stack

• NestJS
• Prisma
• PostgreSQL
• Redis
• Next.js
• React Native
• Expo
• HeroUI
• TypeScript
• Node.js
• Turborepo
• Docker
• Render
• EAS
• Node test runner
• MuMulti-tenant

The problem

Developers keep API keys, certificates and .env files in folders, notes or chats. Authsidian stores them next to passwords, encrypted on the device before they leave it, and the server only ever receives ciphertext.

What I built

• The shared crypto core (vault-core): Argon2id to derive the master key, HKDF to split the authentication key from the encryption key, and AES-256-GCM with a random nonce per item.
• The Tauri (Rust) desktop app for macOS and Windows, with biometric unlock and a Downloads-folder watcher that detects sensitive files (.p8, .pem, .p12, .env) and offers to encrypt them into the vault.
• The sync API, which only stores encrypted blobs, with short-lived sessions and refresh-token rotation by family.
• Device pairing by QR code with an X25519 key exchange.
• Authsidian Send: sharing secrets end-to-end encrypted, password-protected and self-destructing.
• The iPhone app (on TestFlight) and the authsidian.com site in Spanish and English.

Architecture

1. Clients: desktop, mobile, extension and web
2. vault-core on device (Argon2id + AES-256-GCM)
3. Sync API (Go)
4. PostgreSQL (encrypted blobs only)
5. Redis (rate limiting and OTP codes)

Challenges and decisions

Results

• Windows and macOS downloads on authsidian.com; the iPhone app is on TestFlight.
• 159 commits in the repository.
• 115 test files across the API and the clients.

Gallery

Stack

• TypeScript
• React
• Go
• Rust
• Tauri
• ZeZero-knowledge
• ArArgon2id
• AEAES-256-GCM
• Vitest
• GitHub Actions

The problem

ProDominicana, the Export and Investment Center of the Dominican Republic, needs a public portal with its services, news, events and transparency pages, and a way for its team to manage that content without depending on a developer.

What I built

• The full backend in NestJS with Prisma and PostgreSQL.
• The admin shell.
• Many of the public views, with the frontend in Next.js.

Architecture

1. Frontend in Next.js
2. NestJS API
3. PostgreSQL + Prisma

Challenges and decisions

Results

• Live at prodominicana.gob.do.

Gallery

Stack

• NestJS
• Prisma
• PostgreSQL
• Next.js
• React
• TypeScript
• Node.js
• Jest

The problem

Exporters and investors need market data, market access, trade and FDI alerts, country profiles and publications in one place. ProInteligencia brings them together, with most of it behind a login.

What I built

• The full backend in NestJS with Prisma and PostgreSQL.
• The admin shell.
• Many of the public views, with the frontend in Next.js.

Architecture

1. Frontend in Next.js
2. NestJS API
3. PostgreSQL + Prisma

Challenges and decisions

Results

• WTPO Awards 2024 · Best Use of IT, 2nd place.
• Live at prointeligencia.prodominicana.gob.do.

Gallery

Stack

• NestJS
• Prisma
• PostgreSQL
• Next.js
• React
• TypeScript
• Node.js
• Jest

The problem

The platform's dashboards were shown with Power BI Embedded. In the project's next phase they had to move to native charts inside the web application itself.

What I built

• I migrated the Power BI Embedded dashboards to native web charts, with Next.js and React.

Architecture

1. Platform data
2. Next.js + React frontend
3. Native charts in the browser

Challenges and decisions

Gallery

Stack

• Next.js
• React
• TypeScript
• PoPower BI
• Jest