update google calendar events in my website and viceversa

Question

Hi..
 
I need help in google calendar. when user added an event in google calendar it should be reflected in my site it means(my site contains gmail login when user logged into my site using gmail the events added in google calendar should be shown in my site also)
 

the same should be viceversa
if he added event in my site it should be shown in my gmail calendar.
 

Thanks in advance.....