Sentence transformation and hypothetical meaning with Wish and Regret.
When speaking hypothetically about a present or future situation with Wish or Regret we put either the auxiliary or the main verb into a past tense. We do not put both if there is an auxillary and a main verb – only the auxiliary.
Present with Wish
I wish he studied more.
I wish he was studying more.
I wish he would study more.
I wish he didn’t make so many mistakes.
Past with Wish
If we are talking about a past situation we use past perfect.
I wish he had studied more.
I wish he hadn’t made so many mistakes.
We don’t use past perfect continuous.
The rule for Regret is different.
This is used for formal announcements and only with certain verbs, for example inform, tell, say.
I regret to tell you that you have not got the job.
We can use either verb+ing or present perfect continuous to talk about the past.
I regret telling her.
I regret having told her.