Well, I'm looking for the logic of how a program like vArranger works.

Not looking for one to just use. Looking to code my own.

So ideally somebody who has composed a style can help me.
By telling me how they write arrangements in a chord channel so that they know it will sound good when transposed by the arranger.

My big problem I need to understand is when the style has a 5 notes chord and the PLAYED chord is major (only 3 notes) - how does the arranger software pick the new octave/halfstep for the extra 2 notes.