Create custom functions in Google Sheet

We are looking to create a dynamic Google Sheet to create product tags for our shopify feed. In a google sheet, we will paste in the latest export of our products data from Shopify. Flat CSV file On another sheet(s) it will use functions and build a new comma list of tags, that we can then manually paste back in and import back into Shopify Each product will have its own single cell of tags to copy in like: ‘Active Life, L, M, S, T-Shirt, Women, Womens, XL, XS, Yoga’ Size Tags (changes frequently) For size tags, it will look at all products with the same ‘handle’ AND also ‘Variant Inventory Qty’. If ‘Variant Inventory Qty’ is > 0 AND ‘Option1 Value’ = M then it will add the tag M to the list. If ‘Title’ CONTAINS one of the words in the ‘Accessories List’ TAB then it will add the tag ‘Accessories’ If ‘Handle’ OR ‘Title’ CONTAINS ‘Cycle’ then add the tag ‘Cycle’ from our TAB called ‘handle-extras’ if there are values, add these values to the tag list If ‘Handle’ OR ‘Title’ CONTAINS ‘Womens’ then add the tag ‘Womens’ If ‘Handle’ OR ‘Title’ CONTAINS ‘Mens’ then add the tag ‘Mens’ If there is a value in ‘Type’ add this as a Tag to the list Add the value of ‘Option2 Value’ to the Tag List The tags are only copied in the first row, see our example, so either this is automated with a new table pulling in the tags, OR I copy and paste it. But no editing will be required to get the tags back into the sheet. The tech / function to create the auto tags will be open for me to view / edit in future / documented lightly.