GUI bootloader

local function main()
  local component_invoke = component.invoke
  local function boot_invoke(address, method, ...)
    local result = table.pack(pcall(component_invoke, address, method, ...))
    if not result[1] then
      return nil, result[2]
    else
      return table.unpack(result, 2, result.n)
    end
  end

  local eeprom = component.list("eeprom")()
  computer.getBootAddress = function()
    return boot_invoke(eeprom, "getData")
  end
  computer.setBootAddress = function(address)
    return boot_invoke(eeprom, "setData", address)
  end

  do
    local screen = component.list("screen")()
    local gpu = component.list("gpu")()
    if gpu and screen then
      boot_invoke(gpu, "bind", screen)
    end
  end

  local function tryLoadFrom(address)
    local handle, reason = boot_invoke(address, "open", "/init.lua")
    if not handle then
      return nil, reason
    end
    local buffer = ""
    repeat
      local data, reason = boot_invoke(address, "read", handle, math.maxinteger or math.huge)
      if not data and reason then
        return nil, reason
      end
      buffer = buffer .. (data or "")
    until not data
    boot_invoke(address, "close", handle)
    return load(buffer, "=init")
  end

  -- Get a list of bootable drives and their names
  local osList = {}
  for address in component.list("filesystem") do
    local label = boot_invoke(address, "getLabel") or "Unnamed Drive"
    table.insert(osList, {address = address, label = label})
  end

  -- Function to display boot menu with a larger grey box around it, centered on the screen
  local function displayBootMenu(selectedIndex)
    local gpu = component.list("gpu")()
    local w, h = boot_invoke(gpu, "getResolution")
    local boxWidth = 60
    local boxHeight = #osList + 4
    local boxX = math.floor((w - boxWidth) / 2)
    local boxY = math.floor((h - boxHeight) / 2)

    -- Draw grey box
    boot_invoke(gpu, "setBackground", 0x888888)
    boot_invoke(gpu, "fill", boxX, boxY, boxWidth, boxHeight, " ")

    -- Draw boot menu options
    boot_invoke(gpu, "setForeground", 0xFFFFFF)
    boot_invoke(gpu, "setBackground", 0x888888) -- Set background color to grey for text
    boot_invoke(gpu, "set", boxX + 2, boxY + 1, "Select OS to boot:")
    for i, os in ipairs(osList) do
      local line = boxY + i + 2
      local textColor = i == selectedIndex and 0xFF0000 or 0xFFFFFF
      boot_invoke(gpu, "setForeground", textColor)
      boot_invoke(gpu, "set", boxX + 2, line, os.label .. " (" .. os.address .. ")")
    end
    computer.beep(1000, 0.10) -- Beep when boot menu appears
  end

  -- Main boot menu logic
  local selectedIndex = math.ceil(#osList / 2) -- Select middle OS initially
  displayBootMenu(selectedIndex)
  while true do
    local event = {computer.pullSignal()}
    if event[1] == "key_down" then
      if event[4] == 200 and selectedIndex > 1 then -- Arrow up
        selectedIndex = selectedIndex - 1
        displayBootMenu(selectedIndex)
      elseif event[4] == 208 and selectedIndex < #osList then -- Arrow down
        selectedIndex = selectedIndex + 1
        displayBootMenu(selectedIndex)
      elseif event[4] == 28 then -- Enter key
        local selectedOS = osList[selectedIndex]
        local init, reason = tryLoadFrom(selectedOS.address)
        if init then
          computer.setBootAddress(selectedOS.address)
          computer.beep(1500, 0.10) -- Beep when booting into the operating system
          return init()  -- Return the result of running loaded code
        else
          print("Failed to boot from " .. selectedOS.label .. ": " .. tostring(reason))
        end
      end
    end
  end
end

main()  -- Call the main function to execute the boot process