E-PL

The problem

A transport operator may not dispatch a vehicle without a waybill and a documented pre-trip medical examination of the driver. Done on paper that is a clipboard at a depot gate at five in the morning, and a filing cabinet nobody can search.

Digitising it is harder than it sounds, in two different directions. The output is a legal document — an improperly registered waybill carries administrative liability — so the signature on it has to be the real, qualified kind. And the examination is not a form: it needs an actual measurement from an actual breathalyzer, which means the device has to be sold, paid for, shipped, and then talk to a phone.

What I built

The compliance core: a Go backend split into an API, a queue consumer and a scheduler, modelling drivers, vehicles, medical and technical checks and the waybills that depend on them, with PDF generation and push, SMS and email notification. Documents are signed through CryptoPro, which is what makes the paperwork count rather than merely exist.

The examination itself, in a Flutter app: pairing with the breathalyzer over Bluetooth LE so the reading comes off the device rather than out of a text field, with camera and video for the remote examination and screenshot capture blocked on the document screens.

And the commerce that has to sit behind selling hardware: a product catalogue and order management, YooKassa acquiring both in the app and server-side, and a full CDEK integration — client, authentication, webhooks and a scheduled job that reconciles shipment status — so a customer orders a device and the fulfilment happens without anyone re-typing anything.

The result

One system that runs from ordering a breathalyzer to it arriving by courier, to a driver blowing into it at the gate, to a signed waybill that stands up to inspection. The mobile app is past its eighteenth release.

It is the clearest example of what I mean by end-to-end: the domain model, the cryptography, the Bluetooth pairing, the payments, the delivery integration and the office web client are all one person's decisions, so the seams between them are designed rather than negotiated.

Stack

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