Will do: it is certain he do it in future.

Would do: it is certain he decide to do now or in future it if he has ability to do and/or knows about it and/or nothing else stop him.

Would have done: it is certain he decide to do in past if he had ability to do and/or knew about it and/or nothing else stop him.

Can do: he have ability to do now or in future.

Could do: he have ability to do now or in future if he decide to do and/or no external condition that stops it being done.

Could have done: he had the ability, he didn’t do in past (maybe there are reasons).

would = intent to do if there is ability.
could = ability to do if there is intent.

• intent: the desire to do and/or the knowledge that it needs to be done and/or no external condition that stops it being done.

“would you like coffee” = If I give to you ability to drink coffee right now, what is your answer, Yes or No?

“I would do it” = If nothing stops me and I have the ability to do, then I do it. This is said with knowledge that some condition must be met before you can do it:
“I would drink that coffee if you give it to me.”
It is letting the listener know that you intend to do action, but it first requires some other thing to happen which gives you ability.