@callback last_modified() :: {:ok, integer()}

Returns the last modified timestamp of the source.

The return value is a UNIX timestamp.

Note, the granularity of the timestamp comparisons is one second.

This function is called by the HTML view to determine whether the source has changed since the last compilation of the module. If the source has changed, the view, along with the related controller and the project's router module, will be recompiled.

This function should be as fast, reliable and lightweight as possible as it is called on each compilation. Above all, in development mode, it will be called on each request.

@callback list_pages() :: {:ok, [PhoenixStatic.Page.t()]}

Returns the content, path and other information for all static pages.