Synnefo » snf-ganeti » ganeti-local

{-| Module describing a node.

    All updates are functional (copy-based) and return a new node with

    updated value.

-}

{-

Copyright (C) 2009, 2010, 2011, 2012 Google Inc.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.

-}

module Ganeti.HTools.Node

  ( Node(..)

  , List

  -- * Constructor

  , create

  -- ** Finalization after data loading

  , buildPeers

  , setIdx

  , setAlias

  , setOffline

  , setXmem

  , setFmem

  , setPri

  , setSec

  , setMdsk

  , setMcpu

  , setPolicy

  -- * Tag maps

  , addTags

  , delTags

  , rejectAddTags

  -- * Instance (re)location

  , removePri

  , removeSec

  , addPri

  , addPriEx

  , addSec

  , addSecEx

  -- * Stats

  , availDisk

  , availMem

  , availCpu

  , iMem

  , iDsk

  , conflictingPrimaries

  -- * Formatting

  , defaultFields

  , showHeader

  , showField

  , list

  -- * Misc stuff

  , AssocList

  , AllocElement

  , noSecondary

  , computeGroups

  ) where

import Data.List hiding (group)

import qualified Data.Map as Map

import qualified Data.Foldable as Foldable

import Data.Ord (comparing)

import Text.Printf (printf)

import qualified Ganeti.HTools.Container as Container

import qualified Ganeti.HTools.Instance as Instance

import qualified Ganeti.HTools.PeerMap as P

import qualified Ganeti.HTools.Types as T

-- * Type declarations

-- | The tag map type.

type TagMap = Map.Map String Int

-- | The node type.

data Node = Node

  { name     :: String    -- ^ The node name

  , alias    :: String    -- ^ The shortened name (for display purposes)

  , tMem     :: Double    -- ^ Total memory (MiB)

  , nMem     :: Int       -- ^ Node memory (MiB)

  , fMem     :: Int       -- ^ Free memory (MiB)

  , xMem     :: Int       -- ^ Unaccounted memory (MiB)

  , tDsk     :: Double    -- ^ Total disk space (MiB)

  , fDsk     :: Int       -- ^ Free disk space (MiB)

  , tCpu     :: Double    -- ^ Total CPU count

  , uCpu     :: Int       -- ^ Used VCPU count

  , spindleCount :: Int   -- ^ Node spindles (spindle_count node parameter)

  , pList    :: [T.Idx]   -- ^ List of primary instance indices

  , sList    :: [T.Idx]   -- ^ List of secondary instance indices

  , idx      :: T.Ndx     -- ^ Internal index for book-keeping

  , peers    :: P.PeerMap -- ^ Pnode to instance mapping

  , failN1   :: Bool      -- ^ Whether the node has failed n1

  , rMem     :: Int       -- ^ Maximum memory needed for failover by

                          -- primaries of this node

  , pMem     :: Double    -- ^ Percent of free memory

  , pDsk     :: Double    -- ^ Percent of free disk

  , pRem     :: Double    -- ^ Percent of reserved memory

  , pCpu     :: Double    -- ^ Ratio of virtual to physical CPUs

  , mDsk     :: Double    -- ^ Minimum free disk ratio

  , loDsk    :: Int       -- ^ Autocomputed from mDsk low disk

                          -- threshold

  , hiCpu    :: Int       -- ^ Autocomputed from mCpu high cpu

                          -- threshold

  , hiSpindles :: Double  -- ^ Auto-computed from policy spindle_ratio

                          -- and the node spindle count

  , instSpindles :: Double -- ^ Spindles used by instances

  , offline  :: Bool      -- ^ Whether the node should not be used for

                          -- allocations and skipped from score

                          -- computations

  , utilPool :: T.DynUtil -- ^ Total utilisation capacity

  , utilLoad :: T.DynUtil -- ^ Sum of instance utilisation

  , pTags    :: TagMap    -- ^ Map of primary instance tags and their count

  , group    :: T.Gdx     -- ^ The node's group (index)

  , iPolicy  :: T.IPolicy -- ^ The instance policy (of the node's group)

  } deriving (Show, Read, Eq)

instance T.Element Node where

  nameOf = name

  idxOf = idx

  setAlias = setAlias

  setIdx = setIdx

  allNames n = [name n, alias n]

-- | A simple name for the int, node association list.

type AssocList = [(T.Ndx, Node)]

-- | A simple name for a node map.

type List = Container.Container Node

-- | A simple name for an allocation element (here just for logistic

-- reasons).

type AllocElement = (List, Instance.Instance, [Node], T.Score)

-- | Constant node index for a non-moveable instance.

noSecondary :: T.Ndx

noSecondary = -1

-- * Helper functions

-- | Add a tag to a tagmap.

addTag :: TagMap -> String -> TagMap

addTag t s = Map.insertWith (+) s 1 t

-- | Add multiple tags.

addTags :: TagMap -> [String] -> TagMap

addTags = foldl' addTag

-- | Adjust or delete a tag from a tagmap.

delTag :: TagMap -> String -> TagMap

delTag t s = Map.update (\v -> if v > 1

                                 then Just (v-1)

                                 else Nothing)

             s t

-- | Remove multiple tags.

delTags :: TagMap -> [String] -> TagMap

delTags = foldl' delTag

-- | Check if we can add a list of tags to a tagmap.

rejectAddTags :: TagMap -> [String] -> Bool

rejectAddTags t = any (`Map.member` t)

-- | Check how many primary instances have conflicting tags. The

-- algorithm to compute this is to sum the count of all tags, then

-- subtract the size of the tag map (since each tag has at least one,

-- non-conflicting instance); this is equivalent to summing the

-- values in the tag map minus one.

conflictingPrimaries :: Node -> Int

conflictingPrimaries (Node { pTags = t }) = Foldable.sum t - Map.size t

-- | Helper function to increment a base value depending on the passed

-- boolean argument.

incIf :: (Num a) => Bool -> a -> a -> a

incIf True  base delta = base + delta

incIf False base _     = base

-- | Helper function to decrement a base value depending on the passed

-- boolean argument.

decIf :: (Num a) => Bool -> a -> a -> a

decIf True  base delta = base - delta

decIf False base _     = base

-- * Initialization functions

-- | Create a new node.

--

-- The index and the peers maps are empty, and will be need to be

-- update later via the 'setIdx' and 'buildPeers' functions.

create :: String -> Double -> Int -> Int -> Double

       -> Int -> Double -> Bool -> Int -> T.Gdx -> Node

create name_init mem_t_init mem_n_init mem_f_init

       dsk_t_init dsk_f_init cpu_t_init offline_init spindles_init

       group_init =

  Node { name = name_init

       , alias = name_init

       , tMem = mem_t_init

       , nMem = mem_n_init

       , fMem = mem_f_init

       , tDsk = dsk_t_init

       , fDsk = dsk_f_init

       , tCpu = cpu_t_init

       , spindleCount = spindles_init

       , uCpu = 0

       , pList = []

       , sList = []

       , failN1 = True

       , idx = -1

       , peers = P.empty

       , rMem = 0

       , pMem = fromIntegral mem_f_init / mem_t_init

       , pDsk = fromIntegral dsk_f_init / dsk_t_init

       , pRem = 0

       , pCpu = 0

       , offline = offline_init

       , xMem = 0

       , mDsk = T.defReservedDiskRatio

       , loDsk = mDskToloDsk T.defReservedDiskRatio dsk_t_init

       , hiCpu = mCpuTohiCpu (T.iPolicyVcpuRatio T.defIPolicy) cpu_t_init

       , hiSpindles = computeHiSpindles (T.iPolicySpindleRatio T.defIPolicy)

                      spindles_init

       , instSpindles = 0

       , utilPool = T.baseUtil

       , utilLoad = T.zeroUtil

       , pTags = Map.empty

       , group = group_init

       , iPolicy = T.defIPolicy

       }

-- | Conversion formula from mDsk\/tDsk to loDsk.

mDskToloDsk :: Double -> Double -> Int

mDskToloDsk mval = floor . (mval *)

-- | Conversion formula from mCpu\/tCpu to hiCpu.

mCpuTohiCpu :: Double -> Double -> Int

mCpuTohiCpu mval = floor . (mval *)

-- | Conversiojn formula from spindles and spindle ratio to hiSpindles.

computeHiSpindles :: Double -> Int -> Double

computeHiSpindles spindle_ratio = (spindle_ratio *) . fromIntegral

-- | Changes the index.

--

-- This is used only during the building of the data structures.

setIdx :: Node -> T.Ndx -> Node

setIdx t i = t {idx = i}

-- | Changes the alias.

--

-- This is used only during the building of the data structures.

setAlias :: Node -> String -> Node

setAlias t s = t { alias = s }

-- | Sets the offline attribute.

setOffline :: Node -> Bool -> Node

setOffline t val = t { offline = val }

-- | Sets the unnaccounted memory.

setXmem :: Node -> Int -> Node

setXmem t val = t { xMem = val }

-- | Sets the max disk usage ratio.

setMdsk :: Node -> Double -> Node

setMdsk t val = t { mDsk = val, loDsk = mDskToloDsk val (tDsk t) }

-- | Sets the max cpu usage ratio. This will update the node's

-- ipolicy, losing sharing (but it should be a seldomly done operation).

setMcpu :: Node -> Double -> Node

setMcpu t val =

  let new_ipol = (iPolicy t) { T.iPolicyVcpuRatio = val }

  in t { hiCpu = mCpuTohiCpu val (tCpu t), iPolicy = new_ipol }

-- | Sets the policy.

setPolicy :: T.IPolicy -> Node -> Node

setPolicy pol node =

  node { iPolicy = pol

       , hiCpu = mCpuTohiCpu (T.iPolicyVcpuRatio pol) (tCpu node)

       , hiSpindles = computeHiSpindles (T.iPolicySpindleRatio pol)

                      (spindleCount node)

       }

-- | Computes the maximum reserved memory for peers from a peer map.

computeMaxRes :: P.PeerMap -> P.Elem

computeMaxRes = P.maxElem

-- | Builds the peer map for a given node.

buildPeers :: Node -> Instance.List -> Node

buildPeers t il =

  let mdata = map

              (\i_idx -> let inst = Container.find i_idx il

                             mem = if Instance.usesSecMem inst

                                     then Instance.mem inst

                                     else 0

                         in (Instance.pNode inst, mem))

              (sList t)

      pmap = P.accumArray (+) mdata

      new_rmem = computeMaxRes pmap

      new_failN1 = fMem t <= new_rmem

      new_prem = fromIntegral new_rmem / tMem t

  in t {peers=pmap, failN1 = new_failN1, rMem = new_rmem, pRem = new_prem}

-- | Assigns an instance to a node as primary and update the used VCPU

-- count, utilisation data and tags map.

setPri :: Node -> Instance.Instance -> Node

setPri t inst = t { pList = Instance.idx inst:pList t

                  , uCpu = new_count

                  , pCpu = fromIntegral new_count / tCpu t

                  , utilLoad = utilLoad t `T.addUtil` Instance.util inst

                  , pTags = addTags (pTags t) (Instance.tags inst)

                  , instSpindles = new_spindles

                  }

  where new_count = Instance.applyIfOnline inst (+ Instance.vcpus inst)

                    (uCpu t )

        new_spindles = instSpindles t + if Instance.usesLocalStorage inst

                                          then 1 else 0

-- | Assigns an instance to a node as secondary without other updates.

setSec :: Node -> Instance.Instance -> Node

setSec t inst = t { sList = Instance.idx inst:sList t

                  , utilLoad = old_load { T.dskWeight = T.dskWeight old_load +

                                          T.dskWeight (Instance.util inst) }

                  , instSpindles = new_spindles

                  }

  where old_load = utilLoad t

        new_spindles = instSpindles t + if Instance.usesLocalStorage inst

                                          then 1 else 0

-- * Update functions

-- | Sets the free memory.

setFmem :: Node -> Int -> Node

setFmem t new_mem =

  let new_n1 = new_mem <= rMem t

      new_mp = fromIntegral new_mem / tMem t

  in t { fMem = new_mem, failN1 = new_n1, pMem = new_mp }

-- | Removes a primary instance.

removePri :: Node -> Instance.Instance -> Node

removePri t inst =

  let iname = Instance.idx inst

      i_online = Instance.notOffline inst

      uses_disk = Instance.usesLocalStorage inst

      new_plist = delete iname (pList t)

      new_mem = incIf i_online (fMem t) (Instance.mem inst)

      new_dsk = incIf uses_disk (fDsk t) (Instance.dsk inst)

      new_spindles = decIf uses_disk (instSpindles t) 1

      new_mp = fromIntegral new_mem / tMem t

      new_dp = fromIntegral new_dsk / tDsk t

      new_failn1 = new_mem <= rMem t

      new_ucpu = decIf i_online (uCpu t) (Instance.vcpus inst)

      new_rcpu = fromIntegral new_ucpu / tCpu t

      new_load = utilLoad t `T.subUtil` Instance.util inst

  in t { pList = new_plist, fMem = new_mem, fDsk = new_dsk

       , failN1 = new_failn1, pMem = new_mp, pDsk = new_dp

       , uCpu = new_ucpu, pCpu = new_rcpu, utilLoad = new_load

       , pTags = delTags (pTags t) (Instance.tags inst)

       , instSpindles = new_spindles

       }

-- | Removes a secondary instance.

removeSec :: Node -> Instance.Instance -> Node

removeSec t inst =

  let iname = Instance.idx inst

      uses_disk = Instance.usesLocalStorage inst

      cur_dsk = fDsk t

      pnode = Instance.pNode inst

      new_slist = delete iname (sList t)

      new_dsk = incIf uses_disk cur_dsk (Instance.dsk inst)

      new_spindles = decIf uses_disk (instSpindles t) 1

      old_peers = peers t

      old_peem = P.find pnode old_peers

      new_peem = decIf (Instance.usesSecMem inst) old_peem (Instance.mem inst)

      new_peers = if new_peem > 0

                    then P.add pnode new_peem old_peers

                    else P.remove pnode old_peers

      old_rmem = rMem t

      new_rmem = if old_peem < old_rmem

                   then old_rmem

                   else computeMaxRes new_peers

      new_prem = fromIntegral new_rmem / tMem t

      new_failn1 = fMem t <= new_rmem

      new_dp = fromIntegral new_dsk / tDsk t

      old_load = utilLoad t

      new_load = old_load { T.dskWeight = T.dskWeight old_load -

                                          T.dskWeight (Instance.util inst) }

  in t { sList = new_slist, fDsk = new_dsk, peers = new_peers

       , failN1 = new_failn1, rMem = new_rmem, pDsk = new_dp

       , pRem = new_prem, utilLoad = new_load

       , instSpindles = new_spindles

       }

-- | Adds a primary instance (basic version).

addPri :: Node -> Instance.Instance -> T.OpResult Node

addPri = addPriEx False

-- | Adds a primary instance (extended version).

addPriEx :: Bool               -- ^ Whether to override the N+1 and

                               -- other /soft/ checks, useful if we

                               -- come from a worse status

                               -- (e.g. offline)

         -> Node               -- ^ The target node

         -> Instance.Instance  -- ^ The instance to add

         -> T.OpResult Node    -- ^ The result of the operation,

                               -- either the new version of the node

                               -- or a failure mode

addPriEx force t inst =

  let iname = Instance.idx inst

      i_online = Instance.notOffline inst

      uses_disk = Instance.usesLocalStorage inst

      cur_dsk = fDsk t

      new_mem = decIf i_online (fMem t) (Instance.mem inst)

      new_dsk = decIf uses_disk cur_dsk (Instance.dsk inst)

      new_spindles = incIf uses_disk (instSpindles t) 1

      new_failn1 = new_mem <= rMem t

      new_ucpu = incIf i_online (uCpu t) (Instance.vcpus inst)

      new_pcpu = fromIntegral new_ucpu / tCpu t

      new_dp = fromIntegral new_dsk / tDsk t

      l_cpu = T.iPolicyVcpuRatio $ iPolicy t

      new_load = utilLoad t `T.addUtil` Instance.util inst

      inst_tags = Instance.tags inst

      old_tags = pTags t

      strict = not force

  in case () of

       _ | new_mem <= 0 -> T.OpFail T.FailMem

         | uses_disk && new_dsk <= 0 -> T.OpFail T.FailDisk

         | uses_disk && mDsk t > new_dp && strict -> T.OpFail T.FailDisk

         | uses_disk && new_spindles > hiSpindles t

             && strict -> T.OpFail T.FailDisk

         | new_failn1 && not (failN1 t) && strict -> T.OpFail T.FailMem

         | l_cpu >= 0 && l_cpu < new_pcpu && strict -> T.OpFail T.FailCPU

         | rejectAddTags old_tags inst_tags -> T.OpFail T.FailTags

         | otherwise ->

           let new_plist = iname:pList t

               new_mp = fromIntegral new_mem / tMem t

               r = t { pList = new_plist, fMem = new_mem, fDsk = new_dsk

                     , failN1 = new_failn1, pMem = new_mp, pDsk = new_dp

                     , uCpu = new_ucpu, pCpu = new_pcpu

                     , utilLoad = new_load

                     , pTags = addTags old_tags inst_tags

                     , instSpindles = new_spindles

                     }

           in T.OpGood r

-- | Adds a secondary instance (basic version).

addSec :: Node -> Instance.Instance -> T.Ndx -> T.OpResult Node

addSec = addSecEx False

-- | Adds a secondary instance (extended version).

addSecEx :: Bool -> Node -> Instance.Instance -> T.Ndx -> T.OpResult Node

addSecEx force t inst pdx =

  let iname = Instance.idx inst

      old_peers = peers t

      old_mem = fMem t

      new_dsk = fDsk t - Instance.dsk inst

      new_spindles = instSpindles t + 1

      secondary_needed_mem = if Instance.usesSecMem inst

                               then Instance.mem inst

                               else 0

      new_peem = P.find pdx old_peers + secondary_needed_mem

      new_peers = P.add pdx new_peem old_peers

      new_rmem = max (rMem t) new_peem

      new_prem = fromIntegral new_rmem / tMem t

      new_failn1 = old_mem <= new_rmem

      new_dp = fromIntegral new_dsk / tDsk t

      old_load = utilLoad t

      new_load = old_load { T.dskWeight = T.dskWeight old_load +

                                          T.dskWeight (Instance.util inst) }

      strict = not force

  in case () of

       _ | not (Instance.hasSecondary inst) -> T.OpFail T.FailDisk

         | new_dsk <= 0 -> T.OpFail T.FailDisk

         | mDsk t > new_dp && strict -> T.OpFail T.FailDisk

         | new_spindles > hiSpindles t && strict -> T.OpFail T.FailDisk

         | secondary_needed_mem >= old_mem && strict -> T.OpFail T.FailMem

         | new_failn1 && not (failN1 t) && strict -> T.OpFail T.FailMem

         | otherwise ->

           let new_slist = iname:sList t

               r = t { sList = new_slist, fDsk = new_dsk

                     , peers = new_peers, failN1 = new_failn1

                     , rMem = new_rmem, pDsk = new_dp

                     , pRem = new_prem, utilLoad = new_load

                     , instSpindles = new_spindles

                     }

           in T.OpGood r

-- * Stats functions

-- | Computes the amount of available disk on a given node.

availDisk :: Node -> Int

availDisk t =

  let _f = fDsk t

      _l = loDsk t

  in if _f < _l

       then 0

       else _f - _l

-- | Computes the amount of used disk on a given node.

iDsk :: Node -> Int

iDsk t = truncate (tDsk t) - fDsk t

-- | Computes the amount of available memory on a given node.

availMem :: Node -> Int

availMem t =

  let _f = fMem t

      _l = rMem t

  in if _f < _l

       then 0

       else _f - _l

-- | Computes the amount of available memory on a given node.

availCpu :: Node -> Int

availCpu t =

  let _u = uCpu t

      _l = hiCpu t

  in if _l >= _u

       then _l - _u

       else 0

-- | The memory used by instances on a given node.

iMem :: Node -> Int

iMem t = truncate (tMem t) - nMem t - xMem t - fMem t

-- * Display functions

-- | Return a field for a given node.

showField :: Node   -- ^ Node which we're querying

          -> String -- ^ Field name

          -> String -- ^ Field value as string

showField t field =

  case field of

    "idx"  -> printf "%4d" $ idx t

    "name" -> alias t

    "fqdn" -> name t

    "status" -> case () of

                  _ | offline t -> "-"

                    | failN1 t -> "*"

                    | otherwise -> " "

    "tmem" -> printf "%5.0f" $ tMem t

    "nmem" -> printf "%5d" $ nMem t

    "xmem" -> printf "%5d" $ xMem t

    "fmem" -> printf "%5d" $ fMem t

    "imem" -> printf "%5d" $ iMem t

    "rmem" -> printf "%5d" $ rMem t

    "amem" -> printf "%5d" $ fMem t - rMem t

    "tdsk" -> printf "%5.0f" $ tDsk t / 1024

    "fdsk" -> printf "%5d" $ fDsk t `div` 1024

    "tcpu" -> printf "%4.0f" $ tCpu t

    "ucpu" -> printf "%4d" $ uCpu t

    "pcnt" -> printf "%3d" $ length (pList t)

    "scnt" -> printf "%3d" $ length (sList t)

    "plist" -> show $ pList t

    "slist" -> show $ sList t

    "pfmem" -> printf "%6.4f" $ pMem t

    "pfdsk" -> printf "%6.4f" $ pDsk t

    "rcpu"  -> printf "%5.2f" $ pCpu t

    "cload" -> printf "%5.3f" uC

    "mload" -> printf "%5.3f" uM

    "dload" -> printf "%5.3f" uD

    "nload" -> printf "%5.3f" uN

    "ptags" -> intercalate "," . map (uncurry (printf "%s=%d")) .

               Map.toList $ pTags t

    "peermap" -> show $ peers t

    "spindle_count" -> show $ spindleCount t

    "hi_spindles" -> show $ hiSpindles t

    "inst_spindles" -> show $ instSpindles t

    _ -> T.unknownField

  where

    T.DynUtil { T.cpuWeight = uC, T.memWeight = uM,

                T.dskWeight = uD, T.netWeight = uN } = utilLoad t

-- | Returns the header and numeric propery of a field.

showHeader :: String -> (String, Bool)

showHeader field =

  case field of

    "idx" -> ("Index", True)

    "name" -> ("Name", False)

    "fqdn" -> ("Name", False)

    "status" -> ("F", False)

    "tmem" -> ("t_mem", True)

    "nmem" -> ("n_mem", True)

    "xmem" -> ("x_mem", True)

    "fmem" -> ("f_mem", True)

    "imem" -> ("i_mem", True)

    "rmem" -> ("r_mem", True)

    "amem" -> ("a_mem", True)

    "tdsk" -> ("t_dsk", True)

    "fdsk" -> ("f_dsk", True)

    "tcpu" -> ("pcpu", True)

    "ucpu" -> ("vcpu", True)

    "pcnt" -> ("pcnt", True)

    "scnt" -> ("scnt", True)

    "plist" -> ("primaries", True)

    "slist" -> ("secondaries", True)

    "pfmem" -> ("p_fmem", True)

    "pfdsk" -> ("p_fdsk", True)

    "rcpu"  -> ("r_cpu", True)

    "cload" -> ("lCpu", True)

    "mload" -> ("lMem", True)

    "dload" -> ("lDsk", True)

    "nload" -> ("lNet", True)

    "ptags" -> ("PrimaryTags", False)

    "peermap" -> ("PeerMap", False)

    "spindle_count" -> ("NodeSpindles", True)

    "hi_spindles" -> ("MaxSpindles", True)

    "inst_spindles" -> ("InstSpindles", True)

    -- TODO: add node fields (group.uuid, group)

    _ -> (T.unknownField, False)

-- | String converter for the node list functionality.

list :: [String] -> Node -> [String]

list fields t = map (showField t) fields

-- | Constant holding the fields we're displaying by default.

defaultFields :: [String]

defaultFields =

  [ "status", "name", "tmem", "nmem", "imem", "xmem", "fmem"

  , "rmem", "tdsk", "fdsk", "tcpu", "ucpu", "pcnt", "scnt"

  , "pfmem", "pfdsk", "rcpu"

  , "cload", "mload", "dload", "nload" ]

-- | Split a list of nodes into a list of (node group UUID, list of

-- associated nodes).

computeGroups :: [Node] -> [(T.Gdx, [Node])]

computeGroups nodes =

  let nodes' = sortBy (comparing group) nodes

      nodes'' = groupBy (\a b -> group a == group b) nodes'

  in map (\nl -> (group (head nl), nl)) nodes''