Read only access, via functions only

Hi all

Is there a away to set up a schema such that a certain role has (1)
read only access to (2) all the tables, but (3) must use predefined
functions to use that access?

Items 1 and 2 are so that the end user doesn't stomp on the data.

I want item 3 in order to force the application programmers (PHP) not
to craft their own select statements but to go through the API

Thoughts? I have about given up, but maybe somebody can make it easy for me.

Running version 8.2.something (stupid Linux Distros)

(I can post code if necessary, I am just feeling a little lazy...)

Thanks
W