Did China help Vietnam rebuild before or after China declared war on Vietnam? Relationship was already tense during the US-Vietnam war between China and Vietnam

Did China help Vietnam rebuild before or after China declared war on Vietnam? Relationship was already tense during the US-Vietnam war between China and Vietnam, it only took 4 years after the US-Vietnam war for China to declare war, and from what I understand it was the Soviet Union that helped rebuild after that point. China's support of Vietnam during the US-Vietnam war was mainly to try and reduce US influence. China literally looted and burned parts of Northern Vietnam on their way out. Interestingly it has some analogs to the current Russian invasion of Ukraine https://time.com/100417/china-vietnam-sino-vietnamese-war-south-china-sea/ https://time.com/100417/china-vietnam-sino-vietnamese-war-so... China believed it would be a quick and easy conflict where they would blitz Hanoi. Instead they fought with outdated and ineffective tactics, failed to use their air forces properly, and could not make it that deep into north Vietnam before being stonewalled by the more experienced Vietnamese. In response China began brutalizing the countryside out of spite, burning crops, killing civilians on sight, booby-trapping civilian structures, demolishing factories, killing livestock.