At first I implemented a test task remotely. After that I was invited for an onsite interview: got a test task based on the one I made remotely first. It took almost whole working day, at the end I presented and explained what I did, how, why and so on. I liked all people I dealt with there and a company in general, they seamed to like me as well.
In some days after that, I was contacted by their Director Product Engineering, he informed that "from their perspective things went very well, and they'd love to have me onboard", but "couldn't make a formal offer until 2 months after that (company policy unfortunately)". We discussed some specific details of an offer and came into agreement. As I had a long notice period at my current job, I had to officially resign here (but decided not to inform Swrve about it as I didn't want to get any additional pressure because of that when finalising all the contract conditions with Swrve). They kept writing me that the offer preparation process was ongoing, but couldn't be complete yet because of some holidays and so on on their side (every time delaying the date a little bit). And finally, very unexpectedly, their Director Product Engineering informed me: "Unfortunately we aren't able to proceed with our offer. Company policy has changed, and we are no longer able to offer work visas to candidates". I had already informed my landlord that I'm going to move out, my current company had hired a person to replace me after my leave, and, as I required a work permit to stay in the current country, I now have to urgently find another job or leave the country in 3 months.
Advise for any future candidates: don't trust any of their words until you get a signed contract. Though, the company itself looked quite promising, and I liked the team.