TopLvLOvr

local loadPool = {
        function()
            os.run( {}, "rom/programs/lua" )
        end
}

-- Feel free to set this to false if you don't want the text printed
local showMessages = true


if os.myEnv then
    if showMessages then
        print"Injection completed successfully"
    end
    -- Remove myEnv to prevent detection
    os.myEnv = nil
    return
end

local prevState = {}

table.size = function(tbl)
    local count = 0
    for _,__ in pairs(tbl) do
        count = count + 1
    end
    return count
end

local function getParentShell()
  local at=0
  while true do
    at=at+1
    local ok,env = pcall(function() return getfenv(at) end)
    if not ok then break end
    if table.size(env) == 1 then
          local i,v = next(env) -- Grab first
          if i == "shell" then
            return v
          end
    end
  end
  return nil
end

local function recover()
    -- Set flag
    os.myEnv = true
    -- Put back the trampled environment
    os.startTimer = prevState.startTimer
    os.shutdown = prevState.shutdown
    os.pullEvent = prevState.pullEvent
    -- Launch shell like nothing happened

    prevState = nil

    term.setCursorPos(1,1)
    term.clear()

    if showMessages then
        -- Feel free to remove this line, It's just a proof thing
        print"Look at me, I load before shell does"
    end

    -- Because we killed rednet, we have to remove it and then reload it
    _G['rednet'] = nil
    os.loadAPI('/rom/apis/rednet')

    local ok, err = pcall( function()
    parallel.waitForAny(
        unpack(loadPool)
    )
    end )
end

os.stage = {}

-- Stages:
-- injected: Overriding os functions
-- shutdown: Shutdown program has been called
-- jstincse: Shell is doing it's just-in-case
-- bioswait: Bios is waiting for a key press
-- biosexit: Bios has quit
-- complete: fully injected


local function setStage(stage)
    os.stage.currentStage = stage
end

local function getStage()
    return os.stage.currentStage
end

local function _os_pullEvent(_filter)
    _filter = _filter or ""
    if _filter == "key" then
        setStage("bioswait")
        return "key", 0
    elseif _filter == "timer" then
        setStage("shutdown")
        return "timer", 0
    end
end

local function _replSleep(dur)
    local timer = prevState.startTimer( dur )
    repeat
        local sEvent, param = prevState.pullEvent( "timer" )
    until param == timer
end

local function _os_shutdown()
    if getStage() == "shutdown" then
        setStage("jstincse")
    elseif getStage() == "bioswait" then
        setStage("biosexit")
    end
    if getStage() == "biosexit" then
        recover()
    end
end

local function _os_startTimer(seconds)
    return 0
end

local function inject()
    prevState.startTimer = os.startTimer
    prevState.shutdown = os.shutdown
    prevState.pullEvent = os.pullEvent
    os.shutdown = _os_shutdown
    os.pullEvent = _os_pullEvent
    os.startTimer = _os_startTimer
    setStage("injected")
    local shellImpl = getParentShell()
    shellImpl.exit()
end

-- Start everything
inject()