entity eck create new property type or/and behaviour I guess everyone here has done what I want multiple times and I am probably just stupid but I can't seem to find it.

So in my drupal 7 installation I want to create an entity with a date property(so all bundles have a date that is set by a user). Perfect scenario is that this date is like the date field with calender to select a date.

I can't find how to do this but that's probably because I have no idea what to look for.

Can someone put me in the right direction for this?

Making it more clear:
I could just add a date field in all bundles but that seems not the best way to me and I would like to learn drupal in it's best practice.

thanks in advance
You can follow the documentation of eck modules. https://www.drupal.org/node/1370980
The last version introduces the concept of behaviour and you can create your own.


Install the module date_popup
Implement the hook hook_ctools_plugin_directory() 
Create your plugin
In the default_widget callback return a renderable array where the #type is date_popup