Will the Caliphate before the Mahdi be tainted or entirely pure?

The apparent meaning of the narrated traditions about the Mahdi indicates that the caliphate preceding him will not be pure, but rather filled with injustice and oppression, as explained in the Hadith of Abu Sa'id al-Khudri: "He will fill the earth with justice and fairness, just as it was filled with oppression and injustice." Although there are weak narrations indicating the deterioration of governance from a caliphate to tyranny before the appearance of the Mahdi, the Mahdi himself will be reformed suddenly in one night, as stated in the Hadith of Ali: "Allah will reform him in one night," meaning He will grant him repentance, success, and guidance. This aligns with what scholars have mentioned regarding the signs of the Mahdi's appearance and the tribulations that precede it.