Scrolling menu

--=VARIABLES========================--
nScreenWidth, nScreenHeight = term.getSize()

nSelect = 1
tTestMenu = {}
--==================================--

-- Takes a menu table formatted as such:
-- tMenu[n] = {sTitle (string), fAssociatedFunction (function)}
-- Prints the menu with the correct highlighting of the options,
-- and scrolls the menu as needed, beggining at xPos, yPos.
function printMenu(tMenu, nSelection, xPos, yPos)
    local nMenuItem_Index = 1 -- The item that is currently being printed by this method.
    -- Check if the menu needs to be scrolled.
    local nScroll = 0 -- Start out the scroll with an initial value of 0, so it won't affect the print loop if no scrolling is necessary.
    -- If the selection is greater than the amount of available lines to print one.
    if nSelection > nScreenHeight then
        nScroll = nSelection - nScreenHeight -- Make sure that the scroll is the amount of lines that the screen cannot accomodate.
    end

    -- Print the menu by looping through the table.
    for nLine = 1, #tMenu do
        nMenuItem_Index = nLine + nScroll
        term.setCursorPos(xPos, yPos + nLine - 1) -- Subtract 1 from the current line to make sure we start on the proper line (yPos).

        -- If the selection is equal to the current option, draw brackets around it to show that it is selected.
        if nSelection == nMenuItem_Index then
            term.write("[" .. tMenu[nMenuItem_Index].sTitle .. "]") -- Print the option with brackets so that the user knows it is selected.
        -- If the selection is not equal to the current option, do not draw brackets around it to show that it is not selected.
        else
            term.write(" " .. tMenu[nMenuItem_Index].sTitle .. " ") -- Print the title of the menu option with spaces around it to compensate for
            -- the lack of brackets (this way all of the options are centered with one another.)
        end

        if nMenuItem_Index == #tMenu then
            return
        end
    end
end

-- Takes a key code and performs the appropriate method respectively to the passed menu.
function handleKeyPress(tMenu, nSelection, nKey)
    -- If the enter key was pressed, then run the function associated with that option.
    if nKey == 28 then
        tMenu[nSelection].fAssociatedFunction()
    -- If the up key was pressed, then move the selection one up.
    elseif nKey == 200 and nSelection > 1 then
        nSelection = nSelection - 1
    -- If the down key was pressed, then move the selection one down.
    elseif nKey == 208 and nSelection < #tMenu then
        nSelection = nSelection + 1
    end

    if nSelection then
        return nSelection
    else
        return 1
    end
end

-- Sets up a dummy table for scroll testing.
function createDummyMenu()
    local tDummyTable = {}

    for nIndex = 1, nScreenHeight * 2 do
        tDummyTable[#tDummyTable+1] = {sTitle = "Option" .. nIndex, fAssociatedFunction = os.shutdown}
    end

    return tDummyTable
end

tTestMenu = createDummyMenu()

function clearScreen()
    term.clear()
    term.setCursorPos(1, 1)
end

local bRunning = true

while bRunning do
    clearScreen()
    printMenu(tTestMenu, nSelect, 1, 1)

    local sEvent, nKey = os.pullEvent("key")
    nSelect = handleKeyPress(tTestMenu, nSelect, nKey)
end