Then, Reagan sold guns to the Contras in Iran who opposed Hezbollah in Lebanon and Sandinista in Nicaragua. This was a volatile time for Iran which had at this point lost trust in both sides of the cold war as the USSR declined and the US-backed regimes were dead and buried, so they really didn't like the CIA fucking around gun smuggling in their back yard AGAIN.
Now, Iranian guns and bombs come from China and Russia. They use those guns and bombs on westerner allies in the region. Sure, you can call that a "transactional relationship" but I doubt the anybody involved would say it's politically unmotivated. Xi Jinping has even paid them multiple personal visits to speak about the various regional affairs.
One could argue that without Chinese support the IRGC would have collapsed long long ago and that China uses Iran as a puppet state.