vim conditional keymap when a tex file is open

I am trying to make a keymap that will call latexmk when .tex is available (it would be better if .tex is the currently open and active buffer)

I tried :

:nnoremap <Leader>lw :if filereadable('*.tex')<cr>up!<cr>:!latexmk -pdf<cr>endif<cr>

when trying to make latexmk -pdf run, but unfortunately, its just prompting those line in the window, and doing nothing like:

~
:if filereadable('*.tex')
: up!
: :call Tex_RunLaTeX()
: endif
Press ENTER or type command to continue

kindly help.

(it will be great, as told, if this can be done when .tex is the currently open and active buffer.)

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