TLCO

local program, args = (select(1, ...)), table.pack(select(2, ...))
if select('#', ...) < 1 then program = 'shell' end

if shell then
    local resolved = shell.resolveProgram(program)

    if not resolved then
        printError('Couldn\'t find program: ' .. program)
        return 1
    end

    program = resolved
end

-- else hope the user knows what they are doing
-- it probably won't even work unless some parent env has shell

local function pullEventAbsolute(filter)
    local data

    while true do
        data = table.pack(coroutine.yield(filter))

        if data[1] == filter then
            return table.unpack(data, 1, data.n)
        end
    end
end

local originalQueueEvent = os.queueEvent
local function onError(err)
    printError(err)
    print('Press any key to continue')
    originalQueueEvent('fast-forward')
    pullEventAbsolute('fast-forward')
    pullEventAbsolute('key')
    os.shutdown()
    os.shutdown()
end

local eventName = 'tlco_' .. tostring(math.random(-20000, 20000))

local originalPrint = print
local originalShutdown = os.shutdown
local originalPullEvent = os.pullEvent

local function restore()
    _G.print = originalPrint
    os.shutdown = originalShutdown
    os.pullEvent = originalPullEvent
end

function _G.print() end -- prevent error text, and "press any key to continue"

local methodUsed = 'Unknown'

function os.shutdown() -- called at end of bios
    pullEventAbsolute(eventName)

    restore()

    -- We have now achieved top-level coroutine override

    term.setTextColor(colors.cyan)
    print('TLCO Activated, ' .. methodUsed .. ' method')
    term.setTextColor(colors.white)

    local preShutdown = os.shutdown

    -- run directly in _G
    local func, err = loadfile(program, nil, _G)
    if not func then return onError(err) end

    local ok, err = pcall(func, table.unpack(args, 1, args.n))
    if not ok then return onError(err) end

    -- Only run os.shutdown if it has changed, for nested TLCOs
    if os.shutdown ~= preShutdown then
        -- Run os.shutdown twice. Why? Because regular bios does it. Sane TLCOs hook the second shutdown after shell exit.
        -- There is no rednet to crash, so TLCO will try to exit the shell. Give them something to hook if they so please.
        -- I don't know why people would nest TLCOs, but maybe they do
        os.shutdown()
        os.shutdown()
    end
end

function os.pullEvent(filter) -- called in middle of bios
    if filter == 'key' then
        -- haha lol
    else
        return originalPullEvent(filter)
    end
end

methodUsed = 'Rednet'

os.queueEvent('modem_message', 0) -- crash rednet
os.queueEvent(eventName)
pullEventAbsolute(eventName) -- wait for the crash

-- If we are still running, try a different method

methodUsed = 'Shell'

do -- Expect two shutdowns
    local hookedShutdown = os.shutdown
    function os.shutdown()
        os.shutdown = hookedShutdown
    end
end

do -- Prevent one second delay caused by rom/programs/shutdown.lua
    local originalSleep = _G.sleep
    function _G.sleep() end

    -- Restore os.sleep once TLCO executes

    local originalRestore = restore
    restore = function()
        originalRestore()
        _G.sleep = originalSleep
    end
end

do -- Exit all shells
    local exited = false

    for i = 1, 100 do
        local ok, fenv = pcall(getfenv, i)
        if ok and fenv.shell then
            fenv.shell.exit()
            exited = true
        end
    end

    if not exited then
        restore()
        printError('TLCO failed: not running under CraftOS')
        return 1
    end
end

os.queueEvent(eventName)