{-# LANGUAGE CPP #-}
{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PatternGuards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}

-- | 'Patch'es on 'Map' that can insert, delete, and move values from one key to
-- another
module Data.Patch.MapWithMove where

import Data.Patch.Class

import Control.Arrow
import Control.Lens hiding (from, to)
import Control.Monad.Trans.State
import Data.Foldable
import Data.Function
import Data.List
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Maybe
#if !MIN_VERSION_base(4,11,0)
import Data.Semigroup (Semigroup (..))
#endif
import qualified Data.Set as Set
import Data.These (These(..))
import Data.Tuple

-- | Patch a Map 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
  { -- | Extract the internal representation of the 'PatchMapWithMove'
    unPatchMapWithMove :: Map k (NodeInfo k v)
  }
  deriving ( Show, Read, 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

makeWrapped ''PatchMapWithMove

instance FunctorWithIndex k (PatchMapWithMove k)
instance FoldableWithIndex k (PatchMapWithMove k)
instance TraversableWithIndex k (PatchMapWithMove k) where
  itraverse = itraversed . Indexed
  itraversed = _Wrapped .> itraversed <. traversed

-- | 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
  }

-- | 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 $
                        fromMaybe (error "PatchMapWithMove.patchThatChangesMap: impossible: fromKs was empty") $
                        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 = (<>)