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

    module Propellor.Property.Restic
    	( ResticRepo (..)
    	, installed
    	, repoExists
    	, init
    	, restored
    	, backup
    	, 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 qualified Propellor.Property.File as File
    import Data.List (intercalate)

    type Url = String

    type ResticParam = String

    data ResticRepo
    	= Direct FilePath
    	| SFTP User HostName FilePath
    	| REST Url

    instance ConfigurableValue ResticRepo where
    	val (Direct fp) = fp
    	val (SFTP u h fp) = "sftp:" ++ val u ++ "@" ++ val h ++ ":" ++ fp
    	val (REST url) = "rest:" ++ url

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

    repoExists :: ResticRepo -> IO Bool
    repoExists repo = boolSystem "restic"
    	[ Param "-r"
    	, File (val repo)
    	, Param "--password-file"
    	, File (getPasswordFile repo)
    	, Param "snapshots"
    	]

    passwordFileDir :: FilePath
    passwordFileDir = "/etc/restic-keys"

    getPasswordFile :: ResticRepo -> FilePath
    getPasswordFile repo = passwordFileDir </> File.configFileName (val repo)

    passwordFileConfigured :: ResticRepo -> Property (HasInfo + UnixLike)
    passwordFileConfigured repo = propertyList "restic password file" $ props
    	& File.dirExists passwordFileDir
    	& File.mode passwordFileDir 0O2700
    	& getPasswordFile repo `File.hasPrivContent` hostContext

    -- | Inits a new restic repository
    init :: ResticRepo -> Property (HasInfo + DebianLike)
    init repo = check (not <$> repoExists repo) (cmdProperty "restic" initargs)
    	`requires` installed
    	`requires` passwordFileConfigured repo
      where
    	initargs =
    		[ "-r"
    		, val repo
    		, "--password-file"
    		, getPasswordFile repo
    		, "init"
    		]

    -- | Restores a directory from a restic 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 -> ResticRepo -> Property (HasInfo + DebianLike)
    restored dir repo = go
    	`requires` init repo
      where
    	go :: Property DebianLike
    	go = property (dir ++ " restored by restic") $ ifM (liftIO needsRestore)
    		( do
    			warningMessage $ dir ++ " is empty/missing; restoring from backup ..."
    			liftIO restore
    		, noChange
    		)

    	needsRestore = isUnpopulated dir

    	restore = withTmpDirIn (takeDirectory dir) "restic-restore" $ \tmpdir -> do
    		ok <- boolSystem "restic"
    			[ Param "-r"
    			, File (val repo)
    			, Param "--password-file"
    			, File (getPasswordFile repo)
    			, Param "restore"
    			, Param "latest"
    			, Param "--target"
    			, File 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 restic 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:
    --
    -- >	& Restic.backup "/srv/git"
    -- >		(Restic.SFTP (User root) (HostName myserver) /mnt/backup/git.restic")
    -- >		Cron.Daily
    -- >		["--exclude=/srv/git/tobeignored"]
    -- >		[Restic.KeepDays 7, Restic.KeepWeeks 4, Restic.KeepMonths 6, Restic.KeepYears 1]
    --
    -- Since restic uses a fair amount of system resources, only one restic
    -- backup job will be run at a time. Other jobs will wait their turns to
    -- run.
    backup :: FilePath -> ResticRepo -> Cron.Times -> [ResticParam] -> [KeepPolicy] -> Property (HasInfo + 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] -> ResticRepo -> Cron.Times -> [ResticParam] -> [KeepPolicy] -> Property (HasInfo + DebianLike)
    backup' dirs repo crontimes extraargs kp = cronjob
    	`describe` desc
    	`requires` init repo
      where
    	desc = val repo ++ " restic backup"
    	cronjob = Cron.niceJob ("restic_backup" ++ intercalate "_" dirs) crontimes (User "root") "/" $
    		"flock " ++ shellEscape lockfile ++ " sh -c " ++ shellEscape backupcmd
    	lockfile = "/var/lock/propellor-restic.lock"
    	backupcmd = intercalate " && " $
    		createCommand
    		: if null kp then [] else [pruneCommand]
    	createCommand = unwords $
    		[ "restic"
    		, "-r"
    		, shellEscape (val repo)
    		, "--password-file"
    		, shellEscape (getPasswordFile repo)
    		]
    		++ map shellEscape extraargs ++
    		[ "backup" ]
    		++ map shellEscape dirs
    	pruneCommand = unwords $
    		[ "restic"
    		, "-r"
    		, shellEscape (val repo)
    		, "--password-file"
    		, shellEscape (getPasswordFile repo)
    		, "forget"
    		, "--prune"
    		]
    		++
    		map keepParam kp

    -- | Constructs a ResticParam that specifies which old backup generations to
    -- keep. By default, all generations are kept. However, when this parameter is
    -- passed to the `backup` property, they will run restic prune to clean out
    -- generations not specified here.
    keepParam :: KeepPolicy -> ResticParam
    keepParam (KeepLast n) = "--keep-last=" ++ val n
    keepParam (KeepHours n) = "--keep-hourly=" ++ val n
    keepParam (KeepDays n) = "--keep-daily=" ++ val n
    keepParam (KeepWeeks n) = "--keep-weekly=" ++ 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 restic's man page for details.
    data KeepPolicy
    	= KeepLast Int
    	| KeepHours Int
    	| KeepDays Int
    	| KeepWeeks Int
    	| KeepMonths Int
    	| KeepYears Int