Need a mixed UTF-8/CP1252 to UTF-8 converter

I have some files that have mixed UTF-8 and CP1252 characters in them; I'd need a command-line utility that will act as a filter and let all valid UTF-8 characters pass, while converting any invalid sequence from CP1252 to UTF-8. Do you know how could I do this?

Thanks in advance

You could've coded such a utility by now.