The phrase "haddest a mind to" is an archaic form of "had a mind to," meaning a desire or intention to do something. The IPA (International Phonetic Alphabet) transcription for "haddest" is /ˈhædɪst/ which is pronounced "hadd-ist." The -est ending was commonly used in Early Modern English to indicate the second person singular present tense, making "haddest" the equivalent of "you had." Nowadays, we use the more modern form "had a mind to" instead.