This structureThe way in which the parts of a sentence, clause or expression are arranged. E.g.: make somebody + infinitive in "The teacher made me rewrite the composition." can express arranged eventA general term expressing that somebody or something does something or that something happens. E.g.: An apple fell on Isaac’s head.s.

The concert was to begin at 6.

However, if the planned event did not happen, we use be to + perfectThe aspect expressing completion. E.g.: He’s finished university. infinitive:

You were to have tidied your room this morning.

BE DUE TO + infinitive
Modals expressing past necessity / obligation HAD TO