{-| Implementation of global N+1 redundancy

-}

{-

Copyright (C) 2015 Google Inc.
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-}

module Ganeti.HTools.GlobalN1
  ( canEvacuateNode
  , redundant
  , allocGlobalN1
  ) where

import Control.Monad (foldM, foldM_)
import qualified Data.Foldable as Foldable
import Data.Function (on)
import Data.List (partition, sortBy)

import Ganeti.BasicTypes (isOk, Result)
import Ganeti.HTools.AlgorithmParams (AlgorithmOptions(..), defaultOptions)
import Ganeti.HTools.Cluster.AllocatePrimitives (allocateOnSingle)
import qualified Ganeti.HTools.Cluster.AllocationSolution as AllocSol
import qualified Ganeti.HTools.Cluster.Evacuate as Evacuate
import Ganeti.HTools.Cluster.Moves (move)
import qualified Ganeti.HTools.Container as Container
import qualified Ganeti.HTools.Instance as Instance
import qualified Ganeti.HTools.Node as Node
import Ganeti.HTools.Types ( IMove(Failover), Ndx, Gdx, Idx, opToResult,
                             FailMode(FailN1) )
import Ganeti.Types ( DiskTemplate(DTDrbd8), diskTemplateMovable
                    , EvacMode(ChangePrimary))

-- | Foldable function describing how a non-DRBD instance
-- is to be evacuated.
evac :: Gdx -> [Ndx]
     -> (Node.List, Instance.List) -> Idx -> Result (Node.List, Instance.List)
evac gdx ndxs (nl, il) idx = do
  let opts = defaultOptions { algIgnoreSoftErrors = True, algEvacMode = True }
      inst = Container.find idx il
  (nl', il', _) <- Evacuate.nodeEvacInstance opts nl il ChangePrimary inst
                     gdx ndxs
  return (nl', il')

-- | Foldable function describing how a non-movable instance is to
-- be recreated on one of the given nodes.
recreate :: [Ndx]
         -> (Node.List, Instance.List)
         -> Instance.Instance
         -> Result (Node.List, Instance.List)
recreate targetnodes (nl, il) inst = do
  let opts = defaultOptions { algIgnoreSoftErrors = True, algEvacMode = True }
      sols = foldl (\cstate ->
                       AllocSol.concatAllocCollections cstate
                       . allocateOnSingle opts nl inst
                   ) AllocSol.emptyAllocCollection targetnodes
      sol = AllocSol.collectionToSolution FailN1 (const True) sols
  alloc <- maybe (fail "No solution found") return $ AllocSol.asSolution sol
  let il' = AllocSol.updateIl il $ Just alloc
      nl' = AllocSol.extractNl nl il $ Just alloc
  return (nl', il')

-- | Decide if a node can be evacuated, i.e., all DRBD instances
-- failed over and all shared/external storage instances moved off
-- to other nodes.
canEvacuateNode :: (Node.List, Instance.List) -> Node.Node -> Bool
canEvacuateNode (nl, il) n = isOk $ do
  let (drbdIdxs, otherIdxs) = partition ((==) DTDrbd8
                                         . Instance.diskTemplate
                                         . flip Container.find il)
                              $ Node.pList n
      (sharedIdxs, nonMoveIdxs) = partition (diskTemplateMovable
                                  . Instance.diskTemplate
                                  . flip Container.find il) otherIdxs
  -- failover all DRBD instances with primaries on n
  (nl', il') <- opToResult
                . foldM move (nl, il) $ map (flip (,) Failover) drbdIdxs
  -- evacuate other instances
  let grp = Node.group n
      escapenodes = filter (/= Node.idx n)
                    . map Node.idx
                    . filter ((== grp) . Node.group)
                    $ Container.elems nl'
  (nl'', il'') <- foldM (evac grp escapenodes) (nl',il') sharedIdxs
  let recreateInstances = sortBy (flip compare `on` Instance.mem)
                          $ map (`Container.find` il'') nonMoveIdxs
  foldM_ (recreate escapenodes) (nl'', il'') recreateInstances

-- | Predicate on wheter a given situation is globally N+1 redundant.
redundant :: Node.List -> Instance.List -> Bool
redundant nl il = Foldable.all (canEvacuateNode (nl, il)) nl

-- | Predicate on wheter an allocation element leads to a globally N+1 redundant
-- state.
allocGlobalN1 :: Node.List -- ^ the original list of nodes
              -> Instance.List -- ^ the original list of instances
              -> AllocSol.GenericAllocElement a -> Bool
allocGlobalN1 nl il alloc =
  let il' = AllocSol.updateIl il $ Just alloc
      nl' = AllocSol.extractNl nl il $ Just alloc
  in redundant nl' il'
