module Data.HashMap.Strict.Extended
  ( module M
  , catMaybes
  , fromListOn
  , unionsAll
  , groupOn
  , groupOnNE
  , differenceOn
  , lpadZip
  , mapKeys
  , unionsWith
  ) where

import           Prelude

import qualified Data.Align          as A
import qualified Data.Foldable       as F

import           Data.Function
import           Data.HashMap.Strict as M
import           Data.Hashable
import           Data.List.NonEmpty  (NonEmpty (..))
import           Data.These

catMaybes :: HashMap k (Maybe v) -> HashMap k v
catMaybes = M.mapMaybe id

fromListOn :: (Eq k, Hashable k) => (v -> k) -> [v] -> HashMap k v
fromListOn f = fromList . Prelude.map (\v -> (f v, v))

-- | Like 'M.unions', but keeping all elements in the result.
unionsAll :: (Eq k, Hashable k, Foldable t) => t (HashMap k v) -> HashMap k (NonEmpty v)
unionsAll = F.foldl' (\a b -> unionWith (<>) a (fmap (:|[]) b)) M.empty

-- | Given a 'Foldable' sequence of values and a function that extracts a key from each value,
-- returns a 'HashMap' that maps each key to a list of all values in the sequence for which the
-- given function produced it.
--
-- >>> groupOn (take 1) ["foo", "bar", "baz"]
-- fromList [("f", ["foo"]), ("b", ["bar", "baz"])]
groupOn :: (Eq k, Hashable k, Foldable t) => (v -> k) -> t v -> HashMap k [v]
groupOn f = fmap F.toList . groupOnNE f

groupOnNE :: (Eq k, Hashable k, Foldable t) => (v -> k) -> t v -> HashMap k (NonEmpty v)
groupOnNE f = Prelude.foldr (\v -> M.alter (Just . (v:|) . maybe [] F.toList) (f v)) M.empty

differenceOn :: (Eq k, Hashable k, Foldable t) => (v -> k) -> t v -> t v -> HashMap k v
differenceOn f = M.difference `on` (fromListOn f . F.toList)

-- | Analogous to 'A.lpadZip', but on 'HashMap's instead of lists.
lpadZip :: (Eq k, Hashable k) => HashMap k a -> HashMap k b -> HashMap k (Maybe a, b)
lpadZip left = catMaybes . flip A.alignWith left \case
  This  _   -> Nothing
  That    b -> Just (Nothing, b)
  These a b -> Just (Just a,  b)

-- | @'mapKeys' f s@ is the map obtained by applying @f@ to each key of @s@.
--
-- The size of the result may be smaller if @f@ maps two or more distinct
-- keys to the same new key.  In this case the value at the greatest of the
-- original keys is retained.
--
-- > mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        == fromList [(4, "b"), (6, "a")]
-- > mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "c"
-- > mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "c"
--
-- copied from https://hackage.haskell.org/package/containers-0.6.4.1/docs/src/Data.Map.Internal.html#mapKeys
mapKeys :: (Ord k2, Hashable k2) => (k1 -> k2) -> HashMap k1 a -> HashMap k2 a
mapKeys f = fromList . foldrWithKey (\k x xs -> (f k, x) : xs) []

-- | The union of a list of maps, with a combining operation:
--   (@'unionsWith' f == 'Prelude.foldl' ('unionWith' f) 'empty'@).
--
-- > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])]
-- >     == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
--
-- copied from https://hackage.haskell.org/package/containers-0.6.4.1/docs/src/Data.Map.Internal.html#unionsWith
unionsWith :: (Foldable f, Hashable k, Ord k) => (a -> a -> a) -> f (HashMap k a) -> HashMap k a
unionsWith f ts
  = F.foldl' (unionWith f) empty ts