local function main()
  local ci, computer, component = component.invoke, computer or require("computer"), require("component")

  local function bi(a, m, ...)
    local r = table.pack(pcall(ci, a, m, ...))
    return r[1] and table.unpack(r, 2, r.n) or nil, r[2]
  end

  local e = component.list("eeprom")()
  computer.getBootAddress = function() return bi(e, "getData") end
  computer.setBootAddress = function(a) return bi(e, "setData", a) end

  local s, g = component.list("screen")(), component.list("gpu")()
  if g and s then bi(g, "bind", s) end

  local function tryLoad(a)
    local h, r = bi(a, "open", "/init.lua")
    if not h then return nil, "Failed to open /init.lua: " .. tostring(r) end
    local b = ""
    repeat
      local d, r = bi(a, "read", h, math.huge)
      if not d and r then bi(a, "close", h) return nil, "Failed to read /init.lua: " .. tostring(r) end
      b = b .. (d or "")
    until not d
    bi(a, "close", h)
    local i, l = load(b, "=init")
    return i or nil, "Failed to load /init.lua: " .. tostring(l)
  end

  local l = {}
  for a in component.list("filesystem") do
    local b = bi(a, "getLabel") or "Unnamed Drive"
    if b ~= "tmpfs" then table.insert(l, { address = a, label = b }) end
  end

  local function displayError(msg)
    local g = component.list("gpu")()
    local w, h = bi(g, "getResolution")
    local boxX, boxY = math.floor((w - 80) / 2), math.floor((h - 6) / 2)
    bi(g, "setBackground", 0x001f3f) bi(g, "fill", boxX, boxY, 80, 6, " ")
    bi(g, "setForeground", 0xFF4500)
    bi(g, "set", boxX + math.floor((80 - #msg) / 2), boxY + 3, msg)
    computer.beep(800, 1) computer.beep(800, 0.5) computer.beep(800, 0.5)
    while computer.pullSignal() ~= "key_down" do end
    computer.shutdown(true)
  end

  local function displayMenu(sI)
    local g = component.list("gpu")()
    local w, h = bi(g, "getResolution")
    local boxX, boxY = math.floor((w - 60) / 2), math.floor((h - (#l + 4)) / 2)
    bi(g, "setBackground", 0x001f3f) bi(g, "fill", boxX, boxY, 60, #l + 4, " ")
    bi(g, "setForeground", 0xFFFFFF)
    bi(g, "set", boxX + 2, boxY + 1, "Select OS to boot:")
    for i, o in ipairs(l) do
      bi(g, "setForeground", i == sI and 0xFFD700 or 0xFFFFFF)
      bi(g, "set", boxX + 2, boxY + i + 2, o.label .. " (" .. o.address .. ")")
    end
    computer.beep(800, 0.1)
  end

  local sI = math.ceil(#l / 2)
  displayMenu(sI)
  while true do
    local e = { computer.pullSignal() }
    if e[1] == "key_down" then
      if e[4] == 200 and sI > 1 then sI = sI - 1 displayMenu(sI)
      elseif e[4] == 208 and sI < #l then sI = sI + 1 displayMenu(sI)
      elseif e[4] == 28 then
        local o = l[sI]
        local i, r = tryLoad(o.address)
        if i then
          computer.setBootAddress(o.address)
          computer.beep(800, 0.2) computer.beep(800, 0.6) computer.beep(800, 0.2)
          return i()
        else
          displayError("ERROR: Unable to boot from " .. o.label .. ". Check the device and try again.")
          computer.beep(800, 0.1) computer.beep(800, 0.1) computer.beep(800, 0.1)
        end
      end
    end
  end
end

main()