XXX Company Inc. is trying to break into the note taking market by bringing a new offering. They will allow users to take notes on their application. The applications has a mobile version, a web version as well as a version where notes can be added via sending an SMS to a particular number. A user can log in with their account in the relevant application on multiple devices, and it is expected that the notes will be synchronized in pseudo real time. Apart from taking notes, users can also share notes with other users, either by browsing the application user directory, or by adding collaborators from other applications. Initially only Facebook will be supported, but there are plans to include Google, Instagram and other 3rd party applications in the future. The application design must support these future additions. Notes can be shared in view mode and edit mode. Notes shared in view mode can only be seen by collaborators, whereas in edit mode the same note can be edited by the creator as well as the collaborators.
“Note contents can be text, images, videos, sound clips, URLs and other future types. Content may be nested at arbitrary levels. Actions, i.e. hiding, showing, marked as 2important, underline, italicising etc., can be done at a level of individual content, as well as in a hierarchical manner. Actions should also be undoable, in a LIFO manner.”
Which two design patterns I can use to solve the design problem mentioned in the bold paragraph?