switching between different inputs

[carbon dude oxide]

hello, i have a small project that i would like to ask a few questions on

i have a vga monitor that i would like to have two devices display onto it and internal vga and external vga (inside my cabinet and an external connector outside) i would like it to switch between the two is a specific way.

when there i nothing connected to the external vga connector i would like it to automatically switch to the internal vga and when something is connected into the external connector i would like it t switch to it even if the internal vga is outputting something kinda like an override switch. how would i g about doing this using solid state methods? (i dont want the annoying clicking of a relay each time it switches

[carbon dude oxide]

im thinking for the detecting that an active device is plugged into the external vga conector is to use a micro to read the voltage on the SDL/SDA line and when it is high it can then decide that there is something plugged into it and allow the switch

[Lightages]

I am not sure that it is worth you trying to design and construct such a device when they are available to purchase  like this one:
http://www.misco.co.uk/Product/137374/Lindy-2-Port-VGA-Auto-Switch

[carbon dude oxide]

im going to be making it with multiple different connectors, (VGA,DVI,HDMI,SCART and many others i just chose VGA as a starting point) i do plan on having this as a singular unit