local component_invoke = component.invoke
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

-- backwards compatibility, may remove later
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)
 if component.type(address) == "filesystem" then
  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.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")
 elseif component.type(address) == "tape_drive" then
  boot_invoke(address,"seek",-math.huge)
  local boottype = boot_invoke(address,"read",1)
  if boottype == "!" then
   local rl = tonumber(boot_invoke(address,"read",8))
   local buffer = boot_invoke(address,"read",rl)
   return load(buffer, "=init")
  end
 elseif component.type(address) == "modem" then
  boot_invoke(address,"open",9671)
  boot_invoke(address,"broadcast",9671,computer.address())
  s=""
  local bt = computer.uptime()
  while bt+10 > computer.uptime() do
   computer.beep()
   local ev={computer.pullSignal(0.5)}
   if ev[1] == "modem_message" and ev[4] == 9671 then
    bt=computer.uptime()
    if ev[6] == "." then break end
    s=s..ev[6]
   end
  end
  if s ~= "" then
   return load(s,"=init")
  end
 end
end

local bootdevs = {}
for address in component.list("filesystem") do
 bootdevs[#bootdevs+1] = address
end
for address in component.list("tape_drive") do
 bootdevs[#bootdevs+1] = address
end
for address in component.list("modem") do
 bootdevs[#bootdevs+1] = address
end

do
 local gA,sA = component.list("gpu")(),component.list("screen")()
 if gA and sA then
 local gP,cy = component.proxy(gA),1
 gP.bind(sA)
 local sx, sy = gP.getResolution()
 local function wl(s)
  gP.set(1,cy,s)
  cy=cy+1
 end
 local cba = computer.getBootAddress()
 local S = "   "
 local function rdraw()
  gP.fill(1,1,sx,sy," ")
  cy=1
  wl("SKS Enhanced BIOS v1")
  wl("Memory: "..tostring(computer.totalMemory()/1024).."K")
  wl(" ")
  for k,v in ipairs(bootdevs) do
  if v == cba then S = " * " else S = "   " end
  local e,l = pcall(component.invoke,v,"getLabel")
  if not e then l = "" end
  wl(S..tostring(k).." "..v.." "..component.type(v).." "..(l or ""))
  end
 end
 rdraw()
 local timer = 5
 local bhc = false
 while computer.uptime() < timer do
  t,_,c,C = computer.pullSignal(0.5)
  if t == "key_down" and c > 48 and c < 58 then
  cba = bootdevs[c-48]
  bhc = true
  rdraw()
  elseif t == "key_down" and c == 32 then
  timer = timer + 10
  elseif t == "key_down" and c == 13 and C == 28 then
  timer = 0
  end
 end
 if bhc then
  computer.setBootAddress(cba)
 end
 end
end

local init, reason
if computer.getBootAddress() then
 init, reason = tryLoadFrom(computer.getBootAddress())
end
if not init then
 computer.setBootAddress()
 for k,address in ipairs(bootdevs) do
  init, reason = tryLoadFrom(address)
  if init then
   computer.setBootAddress(address)
   break
  end
 end
end
if not init then
 error("no bootable medium found" .. (reason and (": " .. tostring(reason)) or ""), 0)
end
computer.beep(1000, 0.2)
init()