How to check the extension of a filename in a bash script?

I am writing a nightly build script in bash.
Everything is fine and dandy except for one little snag:

#!/bin/bash

for file in "$PATH_TO_SOMEWHERE"; do
      if [ -d $file ]
      then
              # do something directory-ish
      else
              if [ "$file" == "*.txt" ]       #  this is the snag
              then
                     # do something txt-ish
              fi
      fi
done;

My problem is determining the file extension and then acting accordingly. I know the issue is in the if-statement, testing for a txt file.

How can I determine if a file has a .txt suffix?

I think you want to say "Are the last four characters of $file equal to .txt?" If so, you can use the following:

if [ "${file: -4}" == ".txt" ]

Note that the space between file: and -4 is required, as the ':-' modifier means something different.