PHP REGEX: how to pad numbers in the middle/end of a string

i have a list of key=>value pairs from a JSON squirt. i sorted the array and i'm left with the following (excerpted relevant cases because they go as high as 92):

dir1summary
dir10summary
dir1summarydue
dir10summarydue
directive1
directive10
directivecode1
directivecode10

what i need to do is: 1) place all the digits at the end and 2) pad them to 2 digits (01,02,&c) so the list ends up looking like this:

directivesummary01
directivesummary10
directivesummarydue01
directivesummarydue10
directive01
directive10
directivecode01
directivecode10

i was hoping to do this with one REGEX statement given the obvious similarity in key names, but i got lost. here's what i have so far:

dir((\d{1,2}(summary|summarydue))|((ective\d{1,2})|(ectivecode\d{1,2})))

...aaaand i'm lost what to do next. how to move on? is there a better compact way to do this?

EDIT: this also means i have to replace 'dir' with 'directive'. it's implied in the result list, but i didnt' make a bullet item for it. also, the REGEX is all i was able to build at RegExer. thus the "lost what to do next" part.

Solution

Match but don't capture dir
Match but don't capture the optional substring ective
Retain zero or more non-digital characters immediately after ective as capture group #1 (this accounts for optional substrings like summarydue)
Retain the whole integer as capture group #2
Retain the remainder of the string as capture group #3

In the custom function, hardcode directive, then append capture group #1 (which may be empty), then capture group #3 (might also be empty), finally left pad capture group #2 with a zero to a maximum length of 2-digits and append that value to the end of the string

Code: (Demo)

$strings = [
    'dir1summary',
    'dir10summary',
    'dir1summarydue',
    'dir10summarydue',
    'directive1',
    'directive10',
    'directivecode1',
    'directivecode10',
];

var_export(
    preg_replace_callback(
        '/dir(?:ective)?(\D*)(\d+)(.*)/',
        function ($m) {
            return "directive{$m[1]}{$m[3]}" . str_pad($m[2], 2, "0", STR_PAD_LEFT);
        },
        $strings
    )
);

Output:

array (
  0 => 'directivesummary01',
  1 => 'directivesummary10',
  2 => 'directivesummarydue01',
  3 => 'directivesummarydue10',
  4 => 'directive01',
  5 => 'directive10',
  6 => 'directivecode01',
  7 => 'directivecode10',
)

Alternatively, you could parse the string with sscanf(), then print the isolated components in the desired format with printf().

Code: (Demo)

foreach ($strings as $string) {
    sscanf($string, '%[^0-9]%d%s', $dir, $num, $str);
    printf("%s%s%02d\n", str_pad($dir, 9, 'ective'), $str, $num);
}
// same result strings as above