{-# LANGUAGE FlexibleContexts, GeneralizedNewtypeDeriving, InstanceSigs,
             RankNTypes, ScopedTypeVariables, TypeFamilies, UndecidableInstances #-}
module Text.Grampa.ContextFree.Memoizing (FailureInfo(..), ResultList(..), Parser(..), BinTree(..),
                                          fromResultList, reparseTails, longest, peg, terminalPEG)
where

import Control.Applicative
import Control.Monad (Monad(..), MonadFail(fail), MonadPlus(..))
import Data.Function (on)
import Data.Foldable (toList)
import Data.Functor.Classes (Show1(..))
import Data.Functor.Compose (Compose(..))
import Data.List (genericLength, maximumBy, nub)
import Data.Monoid (Monoid(mappend, mempty))
import Data.Monoid.Null (MonoidNull(null))
import Data.Monoid.Factorial (FactorialMonoid, length, splitPrimePrefix)
import Data.Monoid.Textual (TextualMonoid)
import qualified Data.Monoid.Factorial as Factorial
import qualified Data.Monoid.Textual as Textual
import Data.Semigroup (Semigroup((<>)))
import Data.Semigroup.Cancellative (LeftReductive(isPrefixOf))
import Data.String (fromString)
import Data.Witherable.Class (Filterable(mapMaybe))

import qualified Text.Parser.Char
import Text.Parser.Char (CharParsing)
import Text.Parser.Combinators (Parsing(..))
import Text.Parser.LookAhead (LookAheadParsing(..))

import qualified Rank2

import Text.Grampa.Class (GrammarParsing(..), MultiParsing(..),
                          DeterministicParsing(..), InputParsing(..), InputCharParsing(..),
                          TailsParsing(parseTails), ParseResults, ParseFailure(..), Expected(..))
import Text.Grampa.Internal (BinTree(..), FailureInfo(..))
import qualified Text.Grampa.PEG.Backtrack.Measured as Backtrack

import Prelude hiding (iterate, length, null, showList, span, takeWhile)

-- | Parser for a context-free grammar with packrat-like sharing of parse results. It does not support left-recursive
-- grammars.
newtype Parser g s r = Parser{applyParser :: [(s, g (ResultList g s))] -> ResultList g s r}

data ResultList g s r = ResultList !(BinTree (ResultInfo g s r)) {-# UNPACK #-} !(FailureInfo s)
data ResultInfo g s r = ResultInfo !Int ![(s, g (ResultList g s))] !r

instance (Show s, Show r) => Show (ResultList g s r) where
   show (ResultList l f) = "ResultList (" ++ shows l (") (" ++ shows f ")")

instance Show s => Show1 (ResultList g s) where
   liftShowsPrec _sp showList _prec (ResultList l f) rest = "ResultList " ++ showList (simplify <$> toList l) (shows f rest)
      where simplify (ResultInfo _ _ r) = r

instance (Show s, Show r) => Show (ResultInfo g s r) where
   show (ResultInfo l _ r) = "(ResultInfo @" ++ show l ++ " " ++ shows r ")"

instance Functor (ResultInfo g s) where
   fmap f (ResultInfo l t r) = ResultInfo l t (f r)

instance Foldable (ResultInfo g s) where
   foldMap f (ResultInfo _ _ r) = f r

instance Traversable (ResultInfo g s) where
   traverse f (ResultInfo l t r) = ResultInfo l t <$> f r

instance Functor (ResultList g s) where
   fmap f (ResultList l failure) = ResultList ((f <$>) <$> l) failure

instance Filterable (ResultList g s) where
   mapMaybe f (ResultList l failure) = ResultList (mapMaybe (traverse f) l) failure

instance Semigroup (ResultList g s r) where
   ResultList rl1 f1 <> ResultList rl2 f2 = ResultList (rl1 <> rl2) (f1 <> f2)

instance Monoid (ResultList g s r) where
   mempty = ResultList mempty mempty
   mappend = (<>)

instance Functor (Parser g i) where
   fmap f (Parser p) = Parser (fmap f . p)
   {-# INLINABLE fmap #-}

instance Applicative (Parser g i) where
   pure a = Parser (\rest-> ResultList (Leaf $ ResultInfo 0 rest a) mempty)
   Parser p <*> Parser q = Parser r where
      r rest = case p rest
               of ResultList results failure -> ResultList mempty failure <> foldMap continue results
      continue (ResultInfo l rest' f) = continue' l f (q rest')
      continue' l f (ResultList rs failure) = ResultList (adjust l f <$> rs) failure
      adjust l f (ResultInfo l' rest' a) = ResultInfo (l+l') rest' (f a)
   {-# INLINABLE pure #-}
   {-# INLINABLE (<*>) #-}

instance Alternative (Parser g i) where
   empty = Parser (\rest-> ResultList mempty $ FailureInfo (genericLength rest) [Expected "empty"])
   Parser p <|> Parser q = Parser r where
      r rest = p rest <> q rest
   {-# INLINABLE (<|>) #-}

instance Filterable (Parser g i) where
   mapMaybe f (Parser p) = Parser (mapMaybe f . p)
   {-# INLINABLE mapMaybe #-}

instance Monad (Parser g i) where
   return = pure
   Parser p >>= f = Parser q where
      q rest = case p rest
               of ResultList results failure -> ResultList mempty failure <> foldMap continue results
      continue (ResultInfo l rest' a) = continue' l (applyParser (f a) rest')
      continue' l (ResultList rs failure) = ResultList (adjust l <$> rs) failure
      adjust l (ResultInfo l' rest' a) = ResultInfo (l+l') rest' a

instance MonadFail (Parser g s) where
   fail msg = Parser p
      where p rest = ResultList mempty (FailureInfo (genericLength rest) [Expected msg])

instance MonadPlus (Parser g s) where
   mzero = empty
   mplus = (<|>)

instance Semigroup x => Semigroup (Parser g s x) where
   (<>) = liftA2 (<>)

instance Monoid x => Monoid (Parser g s x) where
   mempty = pure mempty
   mappend = liftA2 mappend

instance (Eq s, LeftReductive s, FactorialMonoid s) => GrammarParsing (Parser g s) where
   type ParserGrammar (Parser g s) = g
   type GrammarFunctor (Parser g s) = ResultList g s
   parsingResult s = Compose . fromResultList s
   nonTerminal f = Parser p where
      p ((_, d) : _) = f d
      p _ = ResultList mempty (FailureInfo 0 [Expected "NonTerminal at endOfInput"])
   {-# INLINE nonTerminal #-}

instance (Eq s, LeftReductive s, FactorialMonoid s) => TailsParsing (Parser g s) where
   parseTails = applyParser

-- | Memoizing parser guarantees O(n²) performance for grammars with unambiguous productions, but provides no left
-- recursion support.
--
-- @
-- 'parseComplete' :: ("Rank2".'Rank2.Functor' g, 'FactorialMonoid' s) =>
--                  g (Memoizing.'Parser' g s) -> s -> g ('Compose' ('ParseResults' s) [])
-- @
instance (LeftReductive s, FactorialMonoid s) => MultiParsing (Parser g s) where
   type GrammarConstraint (Parser g s) g' = (g ~ g', Rank2.Functor g)
   type ResultFunctor (Parser g s) = Compose (ParseResults s) []
   -- | Returns the list of all possible input prefix parses paired with the remaining input suffix.
   parsePrefix g input = Rank2.fmap (Compose . Compose . fromResultList input) (snd $ head $ parseGrammarTails g input)
   parseComplete :: (Rank2.Functor g, Eq s, FactorialMonoid s) =>
                    g (Parser g s) -> s -> g (Compose (ParseResults s) [])
   parseComplete g input = Rank2.fmap ((snd <$>) . Compose . fromResultList input)
                              (snd $ head $ reparseTails close $ parseGrammarTails g input)
      where close = Rank2.fmap (<* eof) g

parseGrammarTails :: (Rank2.Functor g, FactorialMonoid s) => g (Parser g s) -> s -> [(s, g (ResultList g s))]
parseGrammarTails g input = foldr parseTail [] (Factorial.tails input)
   where parseTail s parsedTail = parsed
            where parsed = (s,d):parsedTail
                  d      = Rank2.fmap (($ parsed) . applyParser) g

reparseTails :: Rank2.Functor g => g (Parser g s) -> [(s, g (ResultList g s))] -> [(s, g (ResultList g s))]
reparseTails _ [] = []
reparseTails final parsed@((s, _):_) = (s, gd):parsed
   where gd = Rank2.fmap (`applyParser` parsed) final

instance (LeftReductive s, FactorialMonoid s) => InputParsing (Parser g s) where
   type ParserInput (Parser g s) = s
   getInput = Parser p
      where p rest@((s, _):_) = ResultList (Leaf $ ResultInfo 0 rest s) mempty
            p [] = ResultList (Leaf $ ResultInfo 0 [] mempty) mempty
   anyToken = Parser p
      where p rest@((s, _):t) = case splitPrimePrefix s
                                of Just (first, _) -> ResultList (Leaf $ ResultInfo 1 t first) mempty
                                   _ -> ResultList mempty (FailureInfo (genericLength rest) [Expected "anyToken"])
            p [] = ResultList mempty (FailureInfo 0 [Expected "anyToken"])
   satisfy predicate = Parser p
      where p rest@((s, _):t) =
               case splitPrimePrefix s
               of Just (first, _) | predicate first -> ResultList (Leaf $ ResultInfo 1 t first) mempty
                  _ -> ResultList mempty (FailureInfo (genericLength rest) [Expected "satisfy"])
            p [] = ResultList mempty (FailureInfo 0 [Expected "satisfy"])
   scan s0 f = Parser (p s0)
      where p s rest@((i, _) : _) = ResultList (Leaf $ ResultInfo l (drop l rest) prefix) mempty
               where (prefix, _, _) = Factorial.spanMaybe' s f i
                     l = Factorial.length prefix
            p _ [] = ResultList (Leaf $ ResultInfo 0 [] mempty) mempty
   take 0 = mempty
   take n = Parser p
      where p rest@((s, _) : _)
               | x <- Factorial.take n s, l <- Factorial.length x, l == n =
                    ResultList (Leaf $ ResultInfo l (drop l rest) x) mempty
            p rest = ResultList mempty (FailureInfo (genericLength rest) [Expected $ "take " ++ show n])
   takeWhile predicate = Parser p
      where p rest@((s, _) : _)
               | x <- Factorial.takeWhile predicate s, l <- Factorial.length x =
                    ResultList (Leaf $ ResultInfo l (drop l rest) x) mempty
            p [] = ResultList (Leaf $ ResultInfo 0 [] mempty) mempty
   takeWhile1 predicate = Parser p
      where p rest@((s, _) : _)
               | x <- Factorial.takeWhile predicate s, l <- Factorial.length x, l > 0 =
                    ResultList (Leaf $ ResultInfo l (drop l rest) x) mempty
            p rest = ResultList mempty (FailureInfo (genericLength rest) [Expected "takeWhile1"])
   string s = Parser p where
      p rest@((s', _) : _)
         | s `isPrefixOf` s' = ResultList (Leaf $ ResultInfo l (Factorial.drop l rest) s) mempty
      p rest = ResultList mempty (FailureInfo (genericLength rest) [ExpectedInput s])
      l = Factorial.length s
   notSatisfy predicate = Parser p
      where p rest@((s, _):_)
               | Just (first, _) <- splitPrimePrefix s, 
                 predicate first = ResultList mempty (FailureInfo (genericLength rest) [Expected "notSatisfy"])
            p rest = ResultList (Leaf $ ResultInfo 0 rest ()) mempty
   {-# INLINABLE string #-}

instance (Show s, TextualMonoid s) => InputCharParsing (Parser g s) where
   satisfyCharInput predicate = Parser p
      where p rest@((s, _):t) =
               case Textual.characterPrefix s
               of Just first | predicate first -> ResultList (Leaf $ ResultInfo 1 t $ Factorial.primePrefix s) mempty
                  _ -> ResultList mempty (FailureInfo (genericLength rest) [Expected "satisfyCharInput"])
            p [] = ResultList mempty (FailureInfo 0 [Expected "satisfyCharInput"])
   scanChars s0 f = Parser (p s0)
      where p s rest@((i, _) : _) = ResultList (Leaf $ ResultInfo l (drop l rest) prefix) mempty
               where (prefix, _, _) = Textual.spanMaybe_' s f i
                     l = Factorial.length prefix
            p _ [] = ResultList (Leaf $ ResultInfo 0 [] mempty) mempty
   takeCharsWhile predicate = Parser p
      where p rest@((s, _) : _)
               | x <- Textual.takeWhile_ False predicate s, l <- Factorial.length x =
                    ResultList (Leaf $ ResultInfo l (drop l rest) x) mempty
            p [] = ResultList (Leaf $ ResultInfo 0 [] mempty) mempty
   takeCharsWhile1 predicate = Parser p
      where p rest@((s, _) : _)
               | x <- Textual.takeWhile_ False predicate s, l <- Factorial.length x, l > 0 =
                    ResultList (Leaf $ ResultInfo l (drop l rest) x) mempty
            p rest = ResultList mempty (FailureInfo (genericLength rest) [Expected "takeCharsWhile1"])
   notSatisfyChar predicate = Parser p
      where p rest@((s, _):_)
               | Just first <- Textual.characterPrefix s, 
                 predicate first = ResultList mempty (FailureInfo (genericLength rest) [Expected "notSatisfyChar"])
            p rest = ResultList (Leaf $ ResultInfo 0 rest ()) mempty

instance MonoidNull s => Parsing (Parser g s) where
   try (Parser p) = Parser q
      where q rest = rewindFailure (p rest)
               where rewindFailure (ResultList rl (FailureInfo _pos _msgs)) =
                        ResultList rl (FailureInfo (genericLength rest) [])
   Parser p <?> msg  = Parser q
      where q rest = replaceFailure (p rest)
               where replaceFailure (ResultList EmptyTree (FailureInfo pos msgs)) =
                        ResultList EmptyTree (FailureInfo pos $ if pos == genericLength rest then [Expected msg] else msgs)
                     replaceFailure rl = rl
   notFollowedBy (Parser p) = Parser (\input-> rewind input (p input))
      where rewind t (ResultList EmptyTree _) = ResultList (Leaf $ ResultInfo 0 t ()) mempty
            rewind t ResultList{} = ResultList mempty (FailureInfo (genericLength t) [Expected "notFollowedBy"])
   skipMany p = go
      where go = pure () <|> p *> go
   unexpected msg = Parser (\t-> ResultList mempty $ FailureInfo (genericLength t) [Expected msg])
   eof = Parser f
      where f rest@((s, _):_)
               | null s = ResultList (Leaf $ ResultInfo 0 rest ()) mempty
               | otherwise = ResultList mempty (FailureInfo (genericLength rest) [Expected "endOfInput"])
            f [] = ResultList (Leaf $ ResultInfo 0 [] ()) mempty

instance MonoidNull s => DeterministicParsing (Parser g s) where
   Parser p <<|> Parser q = Parser r where
      r rest = case p rest
               of rl@(ResultList EmptyTree _failure) -> rl <> q rest
                  rl -> rl
   takeSome p = (:) <$> p <*> takeMany p
   takeMany (Parser p) = Parser (q 0 id) where
      q len acc rest = case p rest
                       of ResultList EmptyTree _failure -> ResultList (Leaf $ ResultInfo len rest (acc [])) mempty
                          ResultList rl _ -> foldMap continue rl
         where continue (ResultInfo len' rest' result) = q (len + len') (acc . (result:)) rest'
   skipAll (Parser p) = Parser (q 0) where
      q len rest = case p rest
                   of ResultList EmptyTree _failure -> ResultList (Leaf $ ResultInfo len rest ()) mempty
                      ResultList rl _failure -> foldMap continue rl
         where continue (ResultInfo len' rest' _) = q (len + len') rest'

instance MonoidNull s => LookAheadParsing (Parser g s) where
   lookAhead (Parser p) = Parser (\input-> rewind input (p input))
      where rewind t (ResultList rl failure) = ResultList (rewindInput t <$> rl) failure
            rewindInput t (ResultInfo _ _ r) = ResultInfo 0 t r

instance (Show s, TextualMonoid s) => CharParsing (Parser g s) where
   satisfy predicate = Parser p
      where p rest@((s, _):t) =
               case Textual.characterPrefix s
               of Just first | predicate first -> ResultList (Leaf $ ResultInfo 1 t first) mempty
                  _ -> ResultList mempty (FailureInfo (genericLength rest) [Expected "Char.satisfy"])
            p [] = ResultList mempty (FailureInfo 0 [Expected "Char.satisfy"])
   string s = Textual.toString (error "unexpected non-character") <$> string (fromString s)
   text t = (fromString . Textual.toString (error "unexpected non-character")) <$> string (Textual.fromText t)

fromResultList :: (Eq s, FactorialMonoid s) => s -> ResultList g s r -> ParseResults s [(s, r)]
fromResultList s (ResultList EmptyTree (FailureInfo pos msgs)) = Left (ParseFailure (length s - pos + 1) (nub msgs))
fromResultList _ (ResultList rl _failure) = Right (f <$> toList rl)
   where f (ResultInfo _ ((s, _):_) r) = (s, r)
         f (ResultInfo _ [] r) = (mempty, r)

-- | Turns a context-free parser into a backtracking PEG parser that consumes the longest possible prefix of the list
-- of input tails, opposite of 'peg'
longest :: Parser g s a -> Backtrack.Parser g [(s, g (ResultList g s))] a
longest p = Backtrack.Parser q where
   q rest = case applyParser p rest
            of ResultList EmptyTree (FailureInfo pos expected) -> Backtrack.NoParse (FailureInfo pos $ map message expected)
               ResultList rs _ -> parsed (maximumBy (compare `on` resultLength) rs)
   resultLength (ResultInfo l _ _) = l
   parsed (ResultInfo l s r) = Backtrack.Parsed l r s
   message (Expected msg) = Expected msg
   message (ExpectedInput s) = ExpectedInput [(s, error "longest")]

-- | Turns a backtracking PEG parser of the list of input tails into a context-free parser, opposite of 'longest'
peg :: Backtrack.Parser g [(s, g (ResultList g s))] a -> Parser g s a
peg p = Parser q where
   q rest = case Backtrack.applyParser p rest
            of Backtrack.Parsed l result suffix -> ResultList (Leaf $ ResultInfo l suffix result) mempty
               Backtrack.NoParse (FailureInfo pos expected) -> ResultList mempty (FailureInfo pos ((fst . head <$>) <$> expected))

-- | Turns a backtracking PEG parser into a context-free parser
terminalPEG :: Monoid s => Backtrack.Parser g s a -> Parser g s a
terminalPEG p = Parser q where
   q [] = case Backtrack.applyParser p mempty
            of Backtrack.Parsed l result _ -> ResultList (Leaf $ ResultInfo l [] result) mempty
               Backtrack.NoParse failure -> ResultList mempty failure
   q rest@((s, _):_) = case Backtrack.applyParser p s
                       of Backtrack.Parsed l result _ -> ResultList (Leaf $ ResultInfo l (drop l rest) result) mempty
                          Backtrack.NoParse failure -> ResultList mempty failure