I can differentiate which would be used in sentences, but I can't quite pinpoint the difference between these. So I went online and tried a quiz from the British Council and I can't quite figure out why
"I promised my teacher, I would have finished the homework by Monday."
"I promised my teacher, I will have finished the homework by Monday."
It would be a great help if anyone could help me define the lines between will, would have, and would (in a general sense, like tense-wise), and also why will have is wrong in that context.