src/Ganeti/Utils/MultiMap.hs

{-# LANGUAGE RankNTypes, TypeFamilies #-}

{-| Implements multi-maps - maps that map keys to sets of values

This module uses the standard naming convention as other collection-like
libraries and is meant to be imported qualified.

-}

{-

Copyright (C) 2014 Google Inc.
All rights reserved.

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2. Redistributions in binary form must reproduce the above copyright
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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-}

module Ganeti.Utils.MultiMap
  ( MultiMap()
  , multiMap
  , multiMapL
  , multiMapValueL
  , null
  , findValue
  , elem
  , lookup
  , member
  , insert
  , fromList
  , delete
  , deleteAll
  , values
  ) where

import Prelude ()
import Ganeti.Prelude hiding (lookup, null, elem)

import Control.Monad
import qualified Data.Foldable as F
import qualified Data.Map as M
import Data.Maybe (fromMaybe, isJust)
import qualified Data.Set as S
import qualified Text.JSON as J

import Ganeti.Lens

-- | A multi-map that contains multiple values for a single key.
-- It doesn't distinguish non-existent keys and keys with the empty
-- set as the value.
newtype MultiMap k v = MultiMap { getMultiMap :: M.Map k (S.Set v) }
  deriving (Eq, Ord, Show)

instance (Ord v, Ord k) => Monoid (MultiMap k v) where
  mempty = MultiMap M.empty
  mappend (MultiMap x) (MultiMap y) = MultiMap $ M.unionWith S.union x y

instance F.Foldable (MultiMap k) where
  foldMap f = F.foldMap (F.foldMap f) . getMultiMap

instance (J.JSON k, Ord k, J.JSON v, Ord v) => J.JSON (MultiMap k v) where
  showJSON = J.showJSON . getMultiMap
  readJSON = liftM MultiMap . J.readJSON

-- | Creates a multi-map from a map of sets.
multiMap :: (Ord k, Ord v) => M.Map k (S.Set v) -> MultiMap k v
multiMap = MultiMap . M.filter (not . S.null)

-- | A 'Lens' that allows to access a set under a given key in a multi-map.
multiMapL :: (Ord k, Ord v) => k -> Lens' (MultiMap k v) (S.Set v)
multiMapL k f = fmap MultiMap
                 . at k (fmap (mfilter (not . S.null) . Just)
                         . f . fromMaybe S.empty)
                 . getMultiMap
{-# INLINE multiMapL #-}

-- | Return the set corresponding to a given key.
lookup :: (Ord k, Ord v) => k -> MultiMap k v -> S.Set v
lookup = view . multiMapL

-- | Tests if the given key has a non-empty set of values.
member :: (Ord k, Ord v) => k -> MultiMap k v -> Bool
member = (S.null .) . lookup

-- | Tries to find a key corresponding to a given value.
findValue :: (Ord k, Ord v) => v -> MultiMap k v -> Maybe k
findValue v = fmap fst . F.find (S.member v . snd) . M.toList . getMultiMap

-- | Returns 'True' iff a given value is present in a set of some key.
elem :: (Ord k, Ord v) => v -> MultiMap k v -> Bool
elem = (isJust .) . findValue

null :: MultiMap k v -> Bool
null = M.null . getMultiMap

insert :: (Ord k, Ord v) => k -> v -> MultiMap k v -> MultiMap k v
insert k v = set (multiMapValueL k v) True

fromList :: (Ord k, Ord v) => [(k, v)] -> MultiMap k v
fromList = foldr (uncurry insert) mempty

delete :: (Ord k, Ord v) => k -> v -> MultiMap k v -> MultiMap k v
delete k v = set (multiMapValueL k v) False

deleteAll :: (Ord k, Ord v) => k -> MultiMap k v -> MultiMap k v
deleteAll k = set (multiMapL k) S.empty

values :: (Ord k, Ord v) => MultiMap k v -> S.Set v
values =  F.fold . getMultiMap

-- | A 'Lens' that allows to access a given value/key pair in a multi-map.
--
-- It is similar to the 'At' instance, but uses more convenient 'Bool'
-- instead of 'Maybe ()' and a pair key/value.
multiMapValueL :: (Ord k, Ord v) => k -> v -> Lens' (MultiMap k v) Bool
multiMapValueL k v = multiMapL k . atSet v
{-# INLINE multiMapValueL #-}