local w,h = term.getSize()

function printCentred( y, s )
    local x = math.floor((w - string.len(s)) / 2)
    term.setCursorPos(x,y)
    term.clearLine()
    term.write( s )
end

local nOption = 1

-- Display menu
local function drawMenu()
    term.clear()
    term.setCursorPos(1,1)
    term.write( "Wok's Nuclear Reactor Control" )

    term.setCursorPos(w-11,1)
    if nOption == 1 then
    term.write( "1" )
    elseif nOption == 2 then
    term.write( "2" )
    else
    term.write( "3" )
    end
 sleep(0)
end

-- Display the frontend
term.clear()
local function drawFrontend()
    printCentred( math.floor(h/2) - 3, "" )
    printCentred( math.floor(h/2) - 2, "SELECT AN OPTION" )
    printCentred( math.floor(h/2) - 1, "" )
    printCentred( math.floor(h/2) + 0, ((nOption == 1) and "[ Bring Reactors Online ]") or "Bring Reactors Online" )
    printCentred( math.floor(h/2) + 1, ((nOption == 2) and "[ Take Reactors Offline ]") or "Take Reactors Offline" )
    printCentred( math.floor(h/2) + 2, ((nOption == 3) and "[ Logout ]") or "Logout" )
    printCentred( math.floor(h/2) + 3, "" )
end




-- Call functions for display menu
drawMenu()
drawFrontend()



while true do
    local e,p = os.pullEvent()
    if e == "key" then
        local key = p
        if key == 17 or key == 200 then
            -- Up
            if nOption > 1 then
                nOption = nOption - 1
                drawMenu()
                drawFrontend()
            end
        elseif key == 31 or key == 208 then
            -- Down
            if nOption < 3 then -- Change 3 by the number of option.
                nOption = nOption + 1
                drawMenu()
                drawFrontend()
            end
        elseif key == 28 then
            -- Enter
            break
        end
    end
end
term.clear()

-- Conditions
if nOption == 1 then
    term.setCursorPos(1,1)
    print("Engaging reactors...")
	sleep(3)
	shell.run("r-on")
	print("Reactors Online.")
	shell.run("menu")
elseif nOption == 2 then
    term.setCursorPos(1,1)
	print("Disengaging reactors...")
	sleep(2)
	print("Reactors Offline")
	shell.run("r-off")
	shell.run("menu")
else
	term.setCursorPos(1,1)
	print("Logging out...")
	sleep(2)
	os.shutdown()
end