    -- | Maintainer: Félix Sipma <felix+propellor@gueux.org>
    --
    -- Support for the Borg backup tool <https://github.com/borgbackup>

    module Propellor.Property.Borg
    	( BorgParam
    	, BorgRepo(..)
    	, BorgRepoOpt(..)
    	, installed
    	, repoExists
    	, init
    	, restored
    	, backup
    	, KeepPolicy (..)
    	) where

    import Propellor.Base hiding (init)
    import Prelude hiding (init)
    import qualified Propellor.Property.Apt as Apt
    import qualified Propellor.Property.Cron as Cron
    import Data.List (intercalate)

    -- | Parameter to pass to a borg command.
    type BorgParam = String

    -- | A borg repository.
    data BorgRepo
    	-- | Location of the repository, eg
    	-- `BorgRepo "root@myserver:/mnt/backup/git.borg"`
    	= BorgRepo String
    	-- | Location of the repository, and additional options to use
    	-- when accessing the repository.
    	| BorgRepoUsing [BorgRepoOpt] String

    data BorgRepoOpt
    	-- | Use to specify a ssh private key to use when accessing a
    	-- BorgRepo.
    	= UseSshKey FilePath

    repoLoc :: BorgRepo -> String
    repoLoc (BorgRepo s) = s
    repoLoc (BorgRepoUsing _ s) = s

    runBorg :: BorgRepo -> [CommandParam] -> IO Bool
    runBorg repo ps = case runBorgEnv repo of
    	[] -> boolSystem "borg" ps
    	environ -> do
    		environ' <- addEntries environ <$> getEnvironment
    		boolSystemEnv "borg" ps (Just environ')

    runBorgEnv :: BorgRepo -> [(String, String)]
    runBorgEnv (BorgRepo _) = []
    runBorgEnv (BorgRepoUsing os _) = map go os
      where
    	go (UseSshKey k) = ("BORG_RSH", "ssh -i " ++ k)

    installed :: Property DebianLike
    installed = withOS desc $ \w o -> case o of
    	(Just (System (Debian _ (Stable "jessie")) _)) -> ensureProperty w $
    		Apt.installedBackport ["borgbackup"]
    	_ -> ensureProperty w $
    		Apt.installed ["borgbackup"]
      where
            desc = "installed borgbackup"

    repoExists :: BorgRepo -> IO Bool
    repoExists repo = runBorg repo [Param "list", Param (repoLoc repo)]

    -- | Inits a new borg repository
    init :: BorgRepo -> Property DebianLike
    init repo = check (not <$> repoExists repo)
    	(cmdPropertyEnv "borg" initargs (runBorgEnv repo))
    		`requires` installed
      where
    	initargs =
    		[ "init"
    		, repoLoc repo
    		]

    -- | Restores a directory from a borg backup.
    --
    -- Only does anything if the directory does not exist, or exists,
    -- but is completely empty.
    --
    -- The restore is performed atomically; restoring to a temp directory
    -- and then moving it to the directory.
    restored :: FilePath -> BorgRepo -> Property DebianLike
    restored dir repo = go `requires` installed
      where
    	go :: Property DebianLike
    	go = property (dir ++ " restored by borg") $ ifM (liftIO needsRestore)
    		( do
    			warningMessage $ dir ++ " is empty/missing; restoring from backup ..."
    			liftIO restore
    		, noChange
    		)

    	needsRestore = isUnpopulated dir

    	restore = withTmpDirIn (takeDirectory dir) "borg-restore" $ \tmpdir -> do
    		ok <- runBorg repo $
    			[ Param "extract"
    			, Param (repoLoc repo)
    			, Param tmpdir
    			]
    		let restoreddir = tmpdir ++ "/" ++ dir
    		ifM (pure ok <&&> doesDirectoryExist restoreddir)
    			( do
    				void $ tryIO $ removeDirectory dir
    				renameDirectory restoreddir dir
    				return MadeChange
    			, return FailedChange
    			)

    -- | Installs a cron job that causes a given directory to be backed
    -- up, by running borg with some parameters.
    --
    -- If the directory does not exist, or exists but is completely empty,
    -- this Property will immediately restore it from an existing backup.
    --
    -- So, this property can be used to deploy a directory of content
    -- to a host, while also ensuring any changes made to it get backed up.
    -- For example:
    --
    -- >	& Borg.backup "/srv/git"
    -- >		(BorgRepo "root@myserver:/mnt/backup/git.borg")
    -- >		Cron.Daily
    -- >		["--exclude=/srv/git/tobeignored"]
    -- >		[Borg.KeepDays 7, Borg.KeepWeeks 4, Borg.KeepMonths 6, Borg.KeepYears 1]
    --
    -- Note that this property does not initialize the backup repository,
    -- so that will need to be done once, before-hand.
    --
    -- Since borg uses a fair amount of system resources, only one borg
    -- backup job will be run at a time. Other jobs will wait their turns to
    -- run.
    backup :: FilePath -> BorgRepo -> Cron.Times -> [BorgParam] -> [KeepPolicy] -> Property DebianLike
    backup dir repo crontimes extraargs kp = backup' dir repo crontimes extraargs kp
    	`requires` restored dir repo

    -- | Does a backup, but does not automatically restore.
    backup' :: FilePath -> BorgRepo -> Cron.Times -> [BorgParam] -> [KeepPolicy] -> Property DebianLike
    backup' dir repo crontimes extraargs kp = cronjob
    	`describe` desc
    	`requires` installed
      where
    	desc = repoLoc repo ++ " borg backup"
    	cronjob = Cron.niceJob ("borg_backup" ++ dir) crontimes (User "root") "/" $
    		"flock " ++ shellEscape lockfile ++ " sh -c " ++ shellEscape backupcmd
    	lockfile = "/var/lock/propellor-borg.lock"
    	backupcmd = intercalate "&&" $ concat
    		[ concatMap exportenv (runBorgEnv repo)
    		, [createCommand]
    		, if null kp then [] else [pruneCommand]
    		]
    	exportenv (k, v) =
    		[ k ++ "=" ++ shellEscape v
    		, "export " ++ k
    		]
    	createCommand = unwords $
    		[ "borg"
    		, "create"
    		, "--stats"
    		]
    		++ map shellEscape extraargs ++
    		[ shellEscape (repoLoc repo) ++ "::" ++ "$(date --iso-8601=ns --utc)"
    		, shellEscape dir
    		]
    	pruneCommand = unwords $
    		[ "borg"
    		, "prune"
    		, shellEscape (repoLoc repo)
    		]
    		++
    		map keepParam kp

    -- | Constructs an BorgParam that specifies which old backup generations to
    -- keep. By default, all generations are kept. However, when this parameter is
    -- passed to the `backup` property, it will run borg prune to clean out
    -- generations not specified here.
    keepParam :: KeepPolicy -> BorgParam
    keepParam (KeepHours n) = "--keep-hourly=" ++ val n
    keepParam (KeepDays n) = "--keep-daily=" ++ val n
    keepParam (KeepWeeks n) = "--keep-daily=" ++ val n
    keepParam (KeepMonths n) = "--keep-monthly=" ++ val n
    keepParam (KeepYears n) = "--keep-yearly=" ++ val n

    -- | Policy for backup generations to keep. For example, KeepDays 30 will
    -- keep the latest backup for each day when a backup was made, and keep the
    -- last 30 such backups. When multiple KeepPolicies are combined together,
    -- backups meeting any policy are kept. See borg's man page for details.
    data KeepPolicy
    	= KeepHours Int
    	| KeepDays Int
    	| KeepWeeks Int
    	| KeepMonths Int
    	| KeepYears Int