Find out, which mode is in use

See major-mode variable to find out major mode:

Symbol for current buffer’s major mode.

See cond function to do something depending on mode:

Try each clause until one succeeds.

Each clause looks like (CONDITION BODY...). CONDITION is evaluated and, if the value is non-nil, this clause succeeds: then the expressions in BODY are evaluated and the last one’s value is the value of the cond-form. If a clause has one element, as in (CONDITION), then the cond-form returns CONDITION’s value, if that is non-nil. If no clause succeeds, cond returns nil.

E.g.

(cond ((eq major-mode 'lisp-interaction-mode) (message "lisp interaction mode")) ((eq major-mode 'text-mode) (message "text mode"))) 

Also see derived-mode-p function:

(derived-mode-p &rest MODES)

Non-nil if the current major mode is derived from one of MODES.