module Propellor.Property.Reboot (
	now,
	atEnd,
	toDistroKernel,
	toKernelNewerThan,
	KernelVersion,
) where

import Propellor.Base

import Data.List
import Data.Version
import Text.ParserCombinators.ReadP

-- | Kernel version number, in a string. 
type KernelVersion = String

-- | Using this property causes an immediate reboot.
-- 
-- So, this is not a useful property on its own, but it can be useful to
-- compose with other properties. For example:
--
-- > Apt.installed ["new-kernel"]
-- >	`onChange` Reboot.now
now :: Property Linux
now = tightenTargets $ cmdProperty "reboot" []
	`assume` MadeChange
	`describe` "reboot now"

type Force = Bool

-- | Schedules a reboot at the end of the current propellor run.
--
-- The `Result` code of the entire propellor run can be checked;
-- the reboot proceeds only if the function returns True.
--
-- The reboot can be forced to run, which bypasses the init system. Useful
-- if the init system might not be running for some reason.
atEnd :: Force -> (Result -> Bool) -> Property Linux
atEnd force resultok = property "scheduled reboot at end of propellor run" $ do
	endAction "rebooting" atend
	return NoChange
  where
	atend r
		| resultok r = liftIO $ toResult
			<$> boolSystem "reboot" rebootparams
		| otherwise = do
			warningMessage "Not rebooting, due to status of propellor run."
			return FailedChange
	rebootparams
		| force = [Param "--force"]
		| otherwise = []

-- | Reboots immediately if a kernel other than the distro-installed kernel is
-- running.
--
-- This will only work if you have taken measures to ensure that the other
-- kernel won't just get booted again.
-- See 'Propellor.Property.HostingProvider.DigitalOcean'
-- for an example of how to do this.
toDistroKernel :: Property DebianLike
toDistroKernel = check (not <$> runningInstalledKernel) now
	`describe` "running installed kernel"

-- | Given a kernel version string @v@, reboots immediately if the running
-- kernel version is strictly less than @v@ and there is an installed kernel
-- version is greater than or equal to @v@.  Fails if the requested kernel
-- version is not installed.
--
-- For this to be useful, you need to have ensured that the installed kernel
-- with the highest version number is the one that will be started after a
-- reboot.
--
-- This is useful when upgrading to a new version of Debian where you need to
-- ensure that a new enough kernel is running before ensuring other properties.
toKernelNewerThan :: KernelVersion -> Property DebianLike
toKernelNewerThan ver =
	property' ("reboot to kernel newer than " ++ ver) $ \w -> do
		wantV <- tryReadVersion ver
		runningV <- tryReadVersion =<< liftIO runningKernelVersion
		installedV <- maximum <$>
			(mapM tryReadVersion =<< liftIO installedKernelVersions)
		if runningV >= wantV then noChange
			else if installedV >= wantV
				then ensureProperty w now
				else errorMessage $
					"kernel newer than "
					++ ver
					++ " not installed"

runningInstalledKernel :: IO Bool
runningInstalledKernel = do
	kernelver <- runningKernelVersion
	when (null kernelver) $
		error "failed to read uname -r"
	kernelimages <- installedKernelImages
	when (null kernelimages) $
		error "failed to find any installed kernel images"
	findVersion kernelver <$>
		readProcess "file" ("-L" : kernelimages)

runningKernelVersion :: IO KernelVersion
runningKernelVersion = takeWhile (/= '\n') <$> readProcess "uname" ["-r"]

installedKernelImages :: IO [String]
installedKernelImages = concat <$> mapM kernelsIn ["/", "/boot/"]

-- | File output looks something like this, we want to unambiguously
-- match the running kernel version:
--   Linux kernel x86 boot executable bzImage, version 3.16-3-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 3.1, RO-rootFS, swap_dev 0x2, Normal VGA
findVersion :: KernelVersion -> String -> Bool
findVersion ver s = (" version " ++ ver ++ " ") `isInfixOf` s

installedKernelVersions :: IO [KernelVersion]
installedKernelVersions = do
	kernelimages <- installedKernelImages
	when (null kernelimages) $
		error "failed to find any installed kernel images"
	imageLines <- lines <$> readProcess "file" ("-L" : kernelimages)
	return $ extractKernelVersion <$> imageLines

kernelsIn :: FilePath -> IO [FilePath]
kernelsIn d = filter ("vmlinu" `isInfixOf`) <$> dirContents d

extractKernelVersion :: String -> KernelVersion
extractKernelVersion =
	unwords . take 1 . drop 1 . dropWhile (/= "version") . words

readVersionMaybe :: KernelVersion -> Maybe Version
readVersionMaybe ver = case map fst $ readP_to_S parseVersion ver of
	[] -> Nothing
	l -> Just $ maximum l

tryReadVersion :: KernelVersion -> Propellor Version
tryReadVersion ver = case readVersionMaybe ver of
	Just x -> return x
	Nothing -> errorMessage ("couldn't parse version " ++ ver)
