{-# LANGUAGE DeriveFoldable #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE PatternGuards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
-- | 'Patch'es on 'Map' that can insert, delete, and move values from one key to
-- another
module Reflex.Patch.MapWithMove where

import Reflex.Patch.Class

import Control.Arrow
import Control.Monad.State
import Data.Foldable
import Data.Function
import Data.List
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Maybe
import Data.Semigroup (Semigroup (..), (<>))
import qualified Data.Set as Set
import Data.These (These(..))
import Data.Tuple

-- | Patch a DMap with additions, deletions, and moves.  Invariant: If key @k1@
-- is coming from @From_Move k2@, then key @k2@ should be going to @Just k1@,
-- and vice versa.  There should never be any unpaired From/To keys.
newtype PatchMapWithMove k v = PatchMapWithMove (Map k (NodeInfo k v)) deriving (Show, Eq, Ord, Functor, Foldable, Traversable)

-- | Holds the information about each key: where its new value should come from,
-- and where its old value should go to
data NodeInfo k v = NodeInfo
  { _nodeInfo_from :: !(From k v)
    -- ^ Where do we get the new value for this key?
  , _nodeInfo_to :: !(To k)
    -- ^ If the old value is being kept (i.e. moved rather than deleted or
    -- replaced), where is it going?
  }
  deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)

-- | Describe how a key's new value should be produced
data From k v
   = From_Insert v -- ^ Insert the given value here
   | From_Delete -- ^ Delete the existing value, if any, from here
   | From_Move !k -- ^ Move the value here from the given key
   deriving (Show, Read, Eq, Ord, Functor, Foldable, Traversable)

-- | Describe where a key's old value will go.  If this is 'Just', that means
-- the key's old value will be moved to the given other key; if it is 'Nothing',
-- that means it will be deleted.
type To = Maybe

-- | Create a 'PatchMapWithMove', validating it
patchMapWithMove :: Ord k => Map k (NodeInfo k v) -> Maybe (PatchMapWithMove k v)
patchMapWithMove m = if valid then Just $ PatchMapWithMove m else Nothing
  where valid = forwardLinks == backwardLinks
        forwardLinks = Map.mapMaybe _nodeInfo_to m
        backwardLinks = Map.fromList $ catMaybes $ flip fmap (Map.toList m) $ \(to, v) ->
          case _nodeInfo_from v of
            From_Move from -> Just (from, to)
            _ -> Nothing

-- | Create a 'PatchMapWithMove' that inserts everything in the given 'Map'
patchMapWithMoveInsertAll :: Map k v -> PatchMapWithMove k v
patchMapWithMoveInsertAll m = PatchMapWithMove $ flip fmap m $ \v -> NodeInfo
  { _nodeInfo_from = From_Insert v
  , _nodeInfo_to = Nothing
  }

-- | Extract the internal representation of the 'PatchMapWithMove'
unPatchMapWithMove :: PatchMapWithMove k v -> Map k (NodeInfo k v)
unPatchMapWithMove (PatchMapWithMove p) = p

-- | Make a @'PatchMapWithMove' k v@ which has the effect of inserting or updating a value @v@ to the given key @k@, like 'Map.insert'.
insertMapKey :: k -> v -> PatchMapWithMove k v
insertMapKey k v = PatchMapWithMove . Map.singleton k $ NodeInfo (From_Insert v) Nothing

-- |Make a @'PatchMapWithMove' k v@ which has the effect of moving the value from the first key @k@ to the second key @k@, equivalent to:
--
-- @
--     'Map.delete' src (maybe map ('Map.insert' dst) (Map.lookup src map))
-- @
moveMapKey :: Ord k => k -> k -> PatchMapWithMove k v
moveMapKey src dst
  | src == dst = mempty
  | otherwise =
      PatchMapWithMove $ Map.fromList
        [ (dst, NodeInfo (From_Move src) Nothing)
        , (src, NodeInfo From_Delete (Just dst))
        ]

-- |Make a @'PatchMapWithMove' k v@ which has the effect of swapping two keys in the mapping, equivalent to:
--
-- @
--     let aMay = Map.lookup a map
--         bMay = Map.lookup b map
--     in maybe id (Map.insert a) (bMay `mplus` aMay)
--      . maybe id (Map.insert b) (aMay `mplus` bMay)
--      . Map.delete a . Map.delete b $ map
-- @
swapMapKey :: Ord k => k -> k -> PatchMapWithMove k v
swapMapKey src dst
  | src == dst = mempty
  | otherwise =
    PatchMapWithMove $ Map.fromList
      [ (dst, NodeInfo (From_Move src) (Just src))
      , (src, NodeInfo (From_Move dst) (Just dst))
      ]

-- |Make a @'PatchMapWithMove' k v@ which has the effect of deleting a key in the mapping, equivalent to 'Map.delete'.
deleteMapKey :: k -> PatchMapWithMove k v
deleteMapKey k = PatchMapWithMove . Map.singleton k $ NodeInfo From_Delete Nothing

-- | Wrap a @'Map' k (NodeInfo k v)@ representing patch changes into a @'PatchMapWithMove' k v@, without checking any invariants.
--
-- __Warning:__ when using this function, you must ensure that the invariants of 'PatchMapWithMove' are preserved; they will not be checked.
unsafePatchMapWithMove :: Map k (NodeInfo k v) -> PatchMapWithMove k v
unsafePatchMapWithMove = PatchMapWithMove

-- | Apply the insertions, deletions, and moves to a given 'Map'
instance Ord k => Patch (PatchMapWithMove k v) where
  type PatchTarget (PatchMapWithMove k v) = Map k v
  apply (PatchMapWithMove p) old = Just $! insertions `Map.union` (old `Map.difference` deletions) --TODO: return Nothing sometimes --Note: the strict application here is critical to ensuring that incremental merges don't hold onto all their prerequisite events forever; can we make this more robust?
    where insertions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
            From_Insert v -> Just v
            From_Move k -> Map.lookup k old
            From_Delete -> Nothing
          deletions = flip Map.mapMaybeWithKey p $ \_ ni -> case _nodeInfo_from ni of
            From_Delete -> Just ()
            _ -> Nothing

-- | Returns all the new elements that will be added to the 'Map'.
patchMapWithMoveNewElements :: PatchMapWithMove k v -> [v]
patchMapWithMoveNewElements = Map.elems . patchMapWithMoveNewElementsMap

-- | Return a @'Map' k v@ with all the inserts/updates from the given @'PatchMapWithMove' k v@.
patchMapWithMoveNewElementsMap :: PatchMapWithMove k v -> Map k v
patchMapWithMoveNewElementsMap (PatchMapWithMove p) = Map.mapMaybe f p
  where f ni = case _nodeInfo_from ni of
          From_Insert v -> Just v
          From_Move _ -> Nothing
          From_Delete -> Nothing

-- | Create a 'PatchMapWithMove' that, if applied to the given 'Map', will sort
-- its values using the given ordering function.  The set keys of the 'Map' is
-- not changed.
patchThatSortsMapWith :: Ord k => (v -> v -> Ordering) -> Map k v -> PatchMapWithMove k v
patchThatSortsMapWith cmp m = PatchMapWithMove $ Map.fromList $ catMaybes $ zipWith g unsorted sorted
  where unsorted = Map.toList m
        sorted = sortBy (cmp `on` snd) unsorted
        f (to, _) (from, _) = if to == from then Nothing else
          Just (from, to)
        reverseMapping = Map.fromList $ catMaybes $ zipWith f unsorted sorted
        g (to, _) (from, _) = if to == from then Nothing else
          let Just movingTo = Map.lookup to reverseMapping
          in Just (to, NodeInfo (From_Move from) $ Just movingTo)

-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
-- will produce a 'Map' with the same values as the second 'Map' but with the
-- values sorted with the given ordering function.
patchThatChangesAndSortsMapWith :: forall k v. (Ord k, Ord v) => (v -> v -> Ordering) -> Map k v -> Map k v -> PatchMapWithMove k v
patchThatChangesAndSortsMapWith cmp oldByIndex newByIndexUnsorted = patchThatChangesMap oldByIndex newByIndex
  where newList = Map.toList newByIndexUnsorted
        newByIndex = Map.fromList $ zip (fst <$> newList) $ sortBy cmp $ snd <$> newList

-- | Create a 'PatchMapWithMove' that, if applied to the first 'Map' provided,
-- will produce the second 'Map'.
patchThatChangesMap :: (Ord k, Ord v) => Map k v -> Map k v -> PatchMapWithMove k v
patchThatChangesMap oldByIndex newByIndex = patch
  where oldByValue = Map.fromListWith Set.union $ swap . first Set.singleton <$> Map.toList oldByIndex
        (insertsAndMoves, unusedValuesByValue) = flip runState oldByValue $ do
          let f k v = do
                remainingValues <- get
                let putRemainingKeys remainingKeys = put $ if Set.null remainingKeys
                      then Map.delete v remainingValues
                      else Map.insert v remainingKeys remainingValues
                case Map.lookup v remainingValues of
                  Nothing -> return $ NodeInfo (From_Insert v) $ Just undefined -- There's no existing value we can take
                  Just fromKs ->
                    if k `Set.member` fromKs
                    then do
                      putRemainingKeys $ Set.delete k fromKs
                      return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
                    else do
                      (fromK, remainingKeys) <- return . fromJust $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
                      putRemainingKeys remainingKeys
                      return $ NodeInfo (From_Move fromK) $ Just undefined
          Map.traverseWithKey f newByIndex
        unusedOldKeys = fold unusedValuesByValue
        pointlessMove k = \case
          From_Move k' | k == k' -> True
          _ -> False
        keyWasMoved k = if k `Map.member` oldByIndex && not (k `Set.member` unusedOldKeys)
          then Just undefined
          else Nothing
        patch = unsafePatchMapWithMove $ Map.filterWithKey (\k -> not . pointlessMove k . _nodeInfo_from) $ Map.mergeWithKey (\k a _ -> Just $ nodeInfoSetTo (keyWasMoved k) a) (Map.mapWithKey $ \k -> nodeInfoSetTo $ keyWasMoved k) (Map.mapWithKey $ \k _ -> NodeInfo From_Delete $ keyWasMoved k) insertsAndMoves oldByIndex

-- | Change the 'From' value of a 'NodeInfo'
nodeInfoMapFrom :: (From k v -> From k v) -> NodeInfo k v -> NodeInfo k v
nodeInfoMapFrom f ni = ni { _nodeInfo_from = f $ _nodeInfo_from ni }

-- | Change the 'From' value of a 'NodeInfo', using a 'Functor' (or
-- 'Applicative', 'Monad', etc.) action to get the new value
nodeInfoMapMFrom :: Functor f => (From k v -> f (From k v)) -> NodeInfo k v -> f (NodeInfo k v)
nodeInfoMapMFrom f ni = fmap (\result -> ni { _nodeInfo_from = result }) $ f $ _nodeInfo_from ni

-- | Set the 'To' field of a 'NodeInfo'
nodeInfoSetTo :: To k -> NodeInfo k v -> NodeInfo k v
nodeInfoSetTo to ni = ni { _nodeInfo_to = to }

-- |Helper data structure used for composing patches using the monoid instance.
data Fixup k v
   = Fixup_Delete
   | Fixup_Update (These (From k v) (To k))

-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
instance Ord k => Semigroup (PatchMapWithMove k v) where
  PatchMapWithMove ma <> PatchMapWithMove mb = PatchMapWithMove m
    where
      connections = Map.toList $ Map.intersectionWithKey (\_ a b -> (_nodeInfo_to a, _nodeInfo_from b)) ma mb
      h :: (k, (Maybe k, From k v)) -> [(k, Fixup k v)]
      h (_, (mToAfter, editBefore)) = case (mToAfter, editBefore) of
        (Just toAfter, From_Move fromBefore)
          | fromBefore == toAfter
            -> [(toAfter, Fixup_Delete)]
          | otherwise
            -> [ (toAfter, Fixup_Update (This editBefore))
               , (fromBefore, Fixup_Update (That mToAfter))
               ]
        (Nothing, From_Move fromBefore) -> [(fromBefore, Fixup_Update (That mToAfter))] -- The item is destroyed in the second patch, so indicate that it is destroyed in the source map
        (Just toAfter, _) -> [(toAfter, Fixup_Update (This editBefore))]
        (Nothing, _) -> []
      mergeFixups _ Fixup_Delete Fixup_Delete = Fixup_Delete
      mergeFixups _ (Fixup_Update a) (Fixup_Update b)
        | This x <- a, That y <- b
        = Fixup_Update $ These x y
        | That y <- a, This x <- b
        = Fixup_Update $ These x y
      mergeFixups _ _ _ = error "PatchMapWithMove: incompatible fixups"
      fixups = Map.fromListWithKey mergeFixups $ concatMap h connections
      combineNodeInfos _ nia nib = NodeInfo
        { _nodeInfo_from = _nodeInfo_from nia
        , _nodeInfo_to = _nodeInfo_to nib
        }
      applyFixup _ ni = \case
        Fixup_Delete -> Nothing
        Fixup_Update u -> Just $ NodeInfo
          { _nodeInfo_from = fromMaybe (_nodeInfo_from ni) $ getHere u
          , _nodeInfo_to = fromMaybe (_nodeInfo_to ni) $ getThere u
          }
      m = Map.differenceWithKey applyFixup (Map.unionWithKey combineNodeInfos ma mb) fixups
      getHere :: These a b -> Maybe a
      getHere = \case
        This a -> Just a
        These a _ -> Just a
        That _ -> Nothing
      getThere :: These a b -> Maybe b
      getThere = \case
        This _ -> Nothing
        These _ b -> Just b
        That b -> Just b

--TODO: Figure out how to implement this in terms of PatchDMapWithMove rather than duplicating it here
-- |Compose patches having the same effect as applying the patches in turn: @'applyAlways' (p <> q) == 'applyAlways' p . 'applyAlways' q@
instance Ord k => Monoid (PatchMapWithMove k v) where
  mempty = PatchMapWithMove mempty
  mappend = (<>)