Multiple ".csv" to confirm before using "Trigger.txt" for Job Chain to start

Hi,

(Can not find something similar).

The condition I have been given is that before starting the job chain using the trigger file "trigger.txt" the folder should have 4 different ".csv" files.

- Blue.csv

- Red.csv

- Green.csv

- Yellow.csv

- Trigger.txt

So If any file will be missing, Job Chain should not get started.  Please tell me how can I do that. I am very new to CPS Redwood.

Thanks.

Junoon