I purchased this cactus over the weekend from a greenhouse. I have no clue what type of cactus it is. It has 4 yellow flowers on top (which were open when I bought it). The next day it got rainy and cold, and the flowers on top were closed. They have not reopened. Can someone please tell me what type of cactus this is? Also, how long does the flowers bloom and remain open? How can I get it to reopen it's flowers and bloom again? See pictures below. Thanks!