Reading External Calendars

I would like to create an Ionic Page that shows calendar entries. Ideally I could show Monthly, Weekly, Daily and Agenda View, which simply stacks up all the events and allows users to scroll through them.

All of the threads I have read are accessing the native calendar. I want to view external calendars such as a public google calendar or a public .ics calendar. The best example would be viewing a set of school calendars, and allowing the user to select from “School of Business,” “School of Engineering,” and “School of Arts.” Then combine all selected calendars together in one view. But I can’t figure out how to read an external calendar.

Thanks in advance for the help.