Turkey and Russia previously announced their relationship had fully recovered from the previous 18 months. But this week Turkey criticised a Russian bombing in Syria's Idlib province, where Moscow and Ankara are meant to be creating 'de-escalation zones'. At the same time, economic interests seem more aligned than ever... with Turkey agreeing to buy the Russian S-400 missile defence system. That's seen by some as a snub to NATO. These issues are all likely to be on the agenda during Putin's visit to Turkey on Thursday.