How to define a space command to be invisible between two Chinese chars but visible between a Chinese char and an alphabet char?

I would like to define a command which stands for a whitespace between a Chinese char and an alphabet char, such that

1. it produces a whitespace when placed between a Chinese (CJK) char and an alphabet char, whereas
2. it produces nothing when placed between two Chinese chars and
3. (if possible) it produces a whitespace when placed between two alphabet chars.

As far as I know, the ctex macro package could make normal whitespace behave like this, but it is only available when building with XeLaTeX.

Is it possible to define such a command which works with unicode TeX engines (e.g., XeLaTeX and LuaLaTeX)?