os.pullEvent = os.pullEventRaw

local w, h = term.getSize()
local nOption = 1

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

local function drawMenu()
    term.clear()
    term.setCursorPos(1, 1)
    term.write("Doggy OS (13.0)")
    term.setCursorPos(1, 2)
    shell.run("id")

    term.setCursorPos(w - 11, 1)
    if nOption == 1 then
        term.write("Command")
    elseif nOption == 2 then
        term.write("Programs")
    elseif nOption == 3 then
        term.write("Shutdown")
    elseif nOption == 4 then
        term.write("Sign out")
    end
end

-- Icons
local icons = {
    "[C]",  -- Command icon
    "[P]",  -- Programs icon
    "[S]",  -- Shutdown icon
    "[O]"   -- Sign out icon
}

-- GUI
local function drawFrontend()
    term.clear()
    printCentered(math.floor(h / 2) - 3, "")
    printCentered(math.floor(h / 2) - 2, "Start Menu")
    printCentered(math.floor(h / 2) - 1, "")

    for i = 1, 4 do
        local label = (i == 1 and "Command" or i == 2 and "Programs" or i == 3 and "Shutdown" or "Sign out")
        local icon = (nOption == i and " " .. icons[i] .. " " or icons[i])
        printCentered(math.floor(h / 2) + i - 1, (nOption == i and "[ " or "") .. label .. (nOption == i and " ]" or "") .. icon)
    end

    printCentered(math.floor(h / 2) + 5, "")
end

-- Display
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 arrow
            if nOption > 1 then
                nOption = nOption - 1
                drawFrontend()
            end
        elseif key == 31 or key == 208 then  -- Down arrow
            if nOption < 4 then
                nOption = nOption + 1
                drawFrontend()
            end
        elseif key == 28 then  -- Enter key
            break
        end
    end
end

term.clear()

-- Conditions
if nOption == 1 then
    shell.run("/disk/os/home.lua")
elseif nOption == 2 then
    term.clear()
    term.setCursorPos(1, 1)
    shell.run("/disk/os/programs")
elseif nOption == 3 then
    shell.run("/disk/ACPI/shutdown")
else
    shell.run("/disk/ACPI/logoff")
end