gui

-- Since this is a basic indepenant
-- menu, the use of access specifiers
-- are not necessary.
-- Access specifiers in LUA: "local"

nSelect = 1 -- Holds the current selection
nWidth, nHeight = term.getSize() -- Size of the screen

-- You can set up menues within tables
-- however I don't, because I am lazy :P
-- Tables for menues are beneficial (spelling lol)
-- They make your code efficient by allowing for
-- use of the '#' operator.

function cPrint(height, string)
 local xPos = nWidth/2 - string.len(string)/2
 -- The abve line holds the position to print
 -- In the exact center of the screen.

 term.setCursorPos(xPos, height)
 term.write(string)
end

function clear() term.clear(); term.setCursorPos(1, 1) end
-- Clears the screen.

function printMenu()
 -- This is where tables for menues are good
 -- You can call menues in a simple and small
 -- loop. Instead I just right long 'if' 'else'
 -- statements.

 if nSelect == 1 then cPrint(6, "[ Option 1 ]")
 else                 cPrint(6, "  Option 1  ") end

 -- The above checks if we selected this option
 -- If we did then print in the center of the screen
 -- The option with brackets. If we didn't
 -- then print the option in the same spot without
 -- brackets. We put spaces in the non bracketed
 -- options because it prevents the brackets
 -- from not being cleared when we print the options.

 if nSelect == 2 then cPrint(7, "[ Option 2 ]")
 else                 cPrint(7, "  Option 2  ") end

 if nSelect == 3 then cPrint(8, "[ Exit ]")
 else                 cPrint(8, "  Exit  ") end
 -- Always make sure your strings to print
 -- are aligned. It helps :D
end

-- Here is where we loop all of the stuff together
-- literally.


-- When creating infinite loops as the one below
-- it is common practice to have a variable as
-- the condition instead of 'true, but I don't care
-- right now :P.
while true do
 clear() -- Clear the screen to be updated.
 printMenu() -- Update the screen

 event, key = os.pullEvent()

 if event == "key" then
	if key == 200 and nSelect > 1 then nSelect = nSelect-1
	elseif key == 208 and nSelect < 3 then nSelect = nSelect+1
	elseif key == 28 and nSelect == 3 then clear(); print(os.version()); break
	end
 end
end