Butler: cascade due date update to first attachment only if the new due date is before the existing

Question

Hi! Not sure if this has been asked before, or where to look for such information. I would like to setup a main card, which is linked with 2 "sub-cards".  For example, let's take an example:

* Main Card: Kitchen Remodel
* Sub Card 1: Get quote from John
* Sub Card 2: Get quote from Paul

I would link Sub-Card1 (two-way) and Sub-Card2 (two-way) to Main Card. Then, I would like to setup some kind of automation to do the following.

* I would like that if Main Card has no due date, and then if I set SubCard1 due date to 15 Nov, this is cascaded as the Due Date for Main Card. 
* Then, if I set SubCard2's due date is set to 10 Nov, this re-cascades MainCard's due date to 10 Nov.
* If however, I then update SubCard1's due date to 20 Nov, this is not cascaded because it is after the existing due date of 10 Nov.

Is a rule like this possible via Butler, or any other automation method?

Regards,

Karl

Iain Dooley · Answer

@karlcassar I actually do it quite a bit! You can see tonnes of examples of Trellinator snippets here:

https://gist.github.com/iaindooley

I used to create business systems for clients using Butler Bot but I couldn't continue doing that as a consultant so I created Trellinator as a replacement. Later, they retired the bot and the power up was acquired by Trello, and there are many functions that the Bot used to have that are no longer (and apparently will never be) part of the power up so having a way to create custom extensions in a "butler-like" syntax using Google Apps Script is pretty powerful.

karlcassar · Answer

@Iain Dooley Honestly, i'm amazed that you went all that length to submit a code-example for my question, much appreciated. Plus you got me intrigued as it's always good to know there is the possibility of scripting, as it opens up infinite possibilities for automation.  I've updated the code, and this works. Thanks a lot! :)

Iain Dooley · Answer

@karlcassar note that I've updated the gist with corrected code and tested it out (typically I write the Gist and supply the tutorial but don't test the code unless the person comes back and says "I set up the tutorial but the code didn't work" because most of the time people don't run through the tutorial ;)