In all cases, what's "unexpected" is that I was/am happy [on that day/today]. So lets's call that X...
1) I never expected X [to happen, or to be true]
2) I have never expected X
3) I would never expect X
4) I would have never expected X
Idiomatically, #1 above is the normal way of expressing the fact that at no time in the past did the speaker expect X to happen. Note - this form is usually used in contexts where there's a strong implication that X has in fact now happened (X is "true", contrary to the speaker's expectations).
The Present Perfect version #2 doesn't normally carry any implication that X is true. In fact, it's more likely to be used in contexts where X didn't happen (sometimes, where it's just been proven that X could never happen, and the speaker is "boasting" that he always "knew" it wouldn't happen).
Present Perfect implies a strong connection between past and present states (so I have lived here for years implies I still live here now). This creates semantic problems when the unexpected even is itself in the past. Consider, for example, ?I have never expected Trump to win last year. It's hard to see how the speaker could still not be expecting Trump to win, and he certainly can't be boasting about having been proved correct.
Including the modal would in versions #3 and #4 is often just a stylistic device that makes little if any difference to the meaning. Being pedantic, it implies that in the past I never even considered the possibility of X occurring - but if I had thought about it, I would have decided I didn't expect it.
Interestingly, whereas #1 / #2 are primarily distinguished by the fact that the Simple Past form (#1) usually implies X is true, and Present Perfect implies it's not, these implications can be effectively "reversed" when modal would is included. I'm guessing this is because would already implies something hypothetical / unreal / counterfactual - so it's a kind of "secondary negation", cancelling out the negation of "not expected". Consider these default interpretations / implications...
5) I never expected him to hurt her (implies he did hurt her, contrary to my expectations)
6) I have never expected him to hurt her (he hasn't and won't hurt her, as I expected)
7) I would never expect him to hurt her (implies he hasn't and won't hurt her)
8) I would never have expected him to hurt her (implies he did hurt her)