Write a (reverse) filenaming / IPTC metadata utility tool

I want to add IPTC metadata to image files based on their filenames. The files are distributed over a couple of hundred subfolders, and are not named systematically (far from it). License needed only for binary, private, non-exclusive, and one-time use. I want the tool to go through each subdirectory, read the filenames of certain image filetypes (JPEG, TIFF), see if the filenames contain one or more defined search strings, re-format the strings and write the values in the correct IPTC fields of the image file - either add those or append to existing - (e.g. all strings like "1.2.1952" shall be interpreted as a date and put into the "creation date" IPTC field), and remove said string from the filename. I have probably 3 types of string I want to add to three different IPTC fields. Tool should be executable on either current Windows or Mac OS.