Fix wrong extension with `file`

fix_extension.fish

#!/usr/bin/env fish

argparse --name=test "d/dryrun" "p/path=" -- $argv

if test $_flag_d
    echo "Dry running..."
end

if not test -d $_flag_p
    echo "Path not exists: $_flag_p"
    return 1
end

for filename in "$_flag_p/"*
    # check file exists
    if not test -f $filename
        return
    end
    set exts (file --brief --extension $filename)
    set ext_list (string split "/"  $exts)
    # validate extension
    if test $exts != "???" ; and not contains (string sub -s 2 (path extension $filename)) $ext_list
        set new_name (path change-extension $ext_list[1] $filename)
        echo $filename "=>" $new_name
        if not test $_flag_d
            mv "$filename" "$new_name"
        end
    end
end