{-# LANGUAGE UnboxedTuples #-}

-- | Basic parser building blocks.

module FlatParse.Basic.Base
  (
  -- * Bytewise
    eof
  , take
  , take#
  , takeUnsafe#
  , takeRest
  , skip
  , skip#
  , skipBack
  , skipBack#
  , atSkip#
  , atSkipUnsafe#

  -- * Combinators
  , branch
  , notFollowedBy
  , chainl
  , chainr
  , lookahead
  , ensure
  , ensure#
  , withEnsure
  , withEnsure1
  , withEnsure#
  , isolate
  , isolate#
  , isolateUnsafe#

  -- ** Non-specific (TODO)
  , skipMany
  , skipSome

  -- * Errors and failures
  , failed
  , try
  , err
  , withError
  , fails
  , cut
  , cutting
  , optional
  , optional_
  , withOption
  ) where

import Prelude hiding ( take )

import FlatParse.Basic.Parser
import qualified FlatParse.Common.Assorted as Common

import GHC.Exts
import qualified Data.ByteString as B
import qualified Data.ByteString.Internal as B
import GHC.ForeignPtr ( ForeignPtr(..) )
import qualified Control.Applicative

-- | The failing parser. By default, parser choice `(<|>)` arbitrarily backtracks
--   on parser failure.
failed :: ParserT st e a
failed = Control.Applicative.empty
{-# inline failed #-}

-- | Throw a parsing error. By default, parser choice `(<|>)` can't backtrack
--   on parser error. Use `try` to convert an error to a recoverable failure.
err :: e -> ParserT st e a
err e = ParserT \_fp _eob _s st -> Err# st e
{-# inline err #-}

-- | Run the parser, if an error is thrown, handle it with the given function.
withError :: ParserT st e b -> (e -> ParserT st e b) -> ParserT st e b
withError (ParserT f) hdl = ParserT $ \fp eob s st -> case f fp eob s st of
  Err# st' e -> case hdl e of
    ParserT g -> g fp eob s st'
  x -> x
{-# inline withError #-}

-- | Convert a parsing error into failure.
try :: ParserT st e a -> ParserT st e a
try (ParserT f) = ParserT \fp eob s st -> case f fp eob s st of
  Err# st' _ -> Fail# st'
  x          -> x
{-# inline try #-}

-- | Convert a parsing failure to a success.
fails :: ParserT st e a -> ParserT st e ()
fails (ParserT f) = ParserT \fp eob s st ->
  case f fp eob s st of
    OK#   st' _ _ -> Fail# st'
    Fail# st'     -> OK#   st' () s
    Err#  st' e   -> Err#  st' e
{-# inline fails #-}

-- | Convert a parsing failure to an error.
cut :: ParserT st e a -> e -> ParserT st e a
cut (ParserT f) e = ParserT \fp eob s st -> case f fp eob s st of
  Fail# st' -> Err# st' e
  x         -> x
{-# inline cut #-}

-- | Run the parser, if we get a failure, throw the given error, but if we get an error, merge the
--   inner and the newly given errors using the @e -> e -> e@ function. This can be useful for
--   implementing parsing errors which may propagate hints or accummulate contextual information.
cutting :: ParserT st e a -> e -> (e -> e -> e) -> ParserT st e a
cutting (ParserT f) e merge = ParserT \fp eob s st -> case f fp eob s st of
  Fail# st'    -> Err# st' e
  Err#  st' e' -> Err# st' $! merge e' e
  x            -> x
{-# inline cutting #-}

-- | Convert a parsing failure to a `Maybe`. If possible, use `withOption`
--   instead.
optional :: ParserT st e a -> ParserT st e (Maybe a)
optional p = (Just <$> p) <|> pure Nothing
{-# inline optional #-}

-- | Convert a parsing failure to a `()`.
optional_ :: ParserT st e a -> ParserT st e ()
optional_ p = (() <$ p) <|> pure ()
{-# inline optional_ #-}

-- | CPS'd version of `optional`. This is usually more efficient, since it gets
--   rid of the extra `Maybe` allocation.
withOption :: ParserT st e a -> (a -> ParserT st e r) -> ParserT st e r -> ParserT st e r
withOption (ParserT f) just (ParserT nothing) = ParserT \fp eob s st ->
    case f fp eob s st of
      OK#   st' a s -> runParserT# (just a) fp eob s st'
      Fail# st'     -> nothing fp eob s st'
      Err#  st' e   -> Err# st' e
{-# inline withOption #-}

--------------------------------------------------------------------------------

-- | Succeed if the input is empty.
eof :: ParserT st e ()
eof = ParserT \fp eob s st -> case eqAddr# eob s of
  1# -> OK#   st () s
  _  -> Fail# st
{-# inline eof #-}

-- | Save the parsing state, then run a parser, then restore the state.
lookahead :: ParserT st e a -> ParserT st e a
lookahead (ParserT f) = ParserT \fp eob s st ->
  case f fp eob s st of
    OK# st' a _ -> OK# st' a s
    x           -> x
{-# inline lookahead #-}

-- | @isolate n p@ runs the parser @p@ isolated to the next @n@ bytes.
--   All isolated bytes must be consumed.
--
-- Throws a runtime error if given a negative integer.
isolate :: Int -> ParserT st e a -> ParserT st e a
isolate = Common.withIntUnwrap# isolate#
{-# inline isolate #-}

-- | @isolate# n# p@ runs the parser @p@ isolated to the next @n#@ bytes.
--   All isolated bytes must be consumed.
--
-- Throws a runtime error if given a negative integer.
isolate# :: Int# -> ParserT st e a -> ParserT st e a
isolate# n# p = Common.withPosInt# n# (isolateUnsafe# n# p)
{-# inline isolate# #-}

-- | @isolateUnsafe# n# p@ runs the parser @p@ isolated to the next @n#@ bytes.
--   All isolated bytes must be consumed.
--
-- Undefined behaviour if given a negative integer.
isolateUnsafe# :: Int# -> ParserT st e a -> ParserT st e a
isolateUnsafe# n# (ParserT p) =
    withEnsure# n# $ ParserT \fp eob s st ->
        let s' = plusAddr# s n#
        in  case p fp s' s st of
              OK# st' a s'' ->
                case eqAddr# s' s'' of
                  1# -> OK#   st' a s''
                  _  -> Fail# st'
              x -> x
{-# inline isolateUnsafe# #-}

-- | An analogue of the list `foldl` function: first parse a @b@, then parse zero or more @a@-s,
--   and combine the results in a left-nested way by the @b -> a -> b@ function. Note: this is not
--   the usual `chainl` function from the parsec libraries!
chainl :: (b -> a -> b) -> ParserT st e b -> ParserT st e a -> ParserT st e b
chainl f start elem = start >>= go where
  go b = withOption elem (\ !a -> go $! f b a) (pure b)
{-# inline chainl #-}

-- | An analogue of the list `foldr` function: parse zero or more @a@-s, terminated by a @b@, and
--   combine the results in a right-nested way using the @a -> b -> b@ function. Note: this is not
--   the usual `chainr` function from the parsec libraries!
chainr :: (a -> b -> b) -> ParserT st e a -> ParserT st e b -> ParserT st e b
chainr f (ParserT elem) (ParserT end) = ParserT go where
  go fp eob s st = case elem fp eob s st of
    OK#   st' a s -> case go fp eob s st' of
      OK# st'' b s -> let !b' = f a b in OK# st'' b' s
      x            -> x
    Fail# st'     -> end fp eob s st'
    Err#  st' e   -> Err# st' e
{-# inline chainr #-}

-- | Branch on a parser: if the first argument succeeds, continue with the second, else with the third.
--   This can produce slightly more efficient code than `(<|>)`. Moreover, `branch` does not
--   backtrack from the true/false cases.
branch :: ParserT st e a -> ParserT st e b -> ParserT st e b -> ParserT st e b
branch pa pt pf = ParserT \fp eob s st -> case runParserT# pa fp eob s st of
  OK#   st' _ s -> runParserT# pt fp eob s st'
  Fail# st'     -> runParserT# pf fp eob s st'
  Err#  st' e   -> Err# st' e
{-# inline branch #-}

-- | Succeed if the first parser succeeds and the second one fails.
notFollowedBy :: ParserT st e a -> ParserT st e b -> ParserT st e a
notFollowedBy p1 p2 = p1 <* fails p2
{-# inline notFollowedBy #-}

--------------------------------------------------------------------------------

-- | Assert that there are at least @n@ bytes remaining.
--
-- Undefined behaviour if given a negative integer.
ensure :: Int -> ParserT st e ()
ensure = Common.withIntUnwrap# ensure#
{-# inline ensure #-}

-- | Assert that there are at least @n#@ bytes remaining.
--
-- Undefined behaviour if given a negative integer.
ensure# :: Int# -> ParserT st e ()
ensure# n# = withEnsure# n# (pure ())
{-# inline ensure# #-}

-- TODO: András: why do we need withEnsure-s?
-- There's no unboxing to be improved.

-- | Assert that there are at least @n#@ bytes remaining (CPS).
--
-- Undefined behaviour if given a negative integer.
withEnsure :: Int -> ParserT st e r -> ParserT st e r
withEnsure = Common.withIntUnwrap# withEnsure#
{-# inline withEnsure #-}

-- | Assert that there is at least 1 byte remaining (CPS).
--
-- Undefined behaviour if given a negative integer.
withEnsure1 :: ParserT st e r -> ParserT st e r
withEnsure1 (ParserT p) = ParserT \fp eob s st ->
    case eqAddr# eob s of
      0# -> p fp eob s st
      _  -> Fail# st
{-# inline withEnsure1 #-}

-- | Assert that there are at least @n#@ bytes remaining (CPS).
--
-- Undefined behaviour if given a negative integer.
withEnsure# :: Int# -> ParserT st e r -> ParserT st e r
withEnsure# n# (ParserT p) = ParserT \fp eob s st ->
    case n# <=# minusAddr# eob s of
      1# -> p fp eob s st
      _  -> Fail# st
{-# inline withEnsure# #-}

--------------------------------------------------------------------------------

-- | Read the given number of bytes as a 'ByteString'.
--
-- Throws a runtime error if given a negative integer.
--
-- This does no copying. The 'B.ByteString' returned is a "slice" of the input,
-- and will keep it alive. To avoid this, use 'B.copy' on the output.
take :: Int -> ParserT st e B.ByteString
take (I# n#) = take# n#
{-# inline take #-}

-- | Read @n#@ bytes as a 'ByteString'. Fails if fewer than @n#@ bytes are
--   available.
--
-- Throws a runtime error if given a negative integer.
--
-- This does no copying. The 'B.ByteString' returned is a "slice" of the input,
-- and will keep it alive. To avoid this, use 'B.copy' on the output.
take# :: Int# -> ParserT st e B.ByteString
take# n# = Common.withPosInt# n# (takeUnsafe# n#)
{-# inline take# #-}

-- | Read @n#@ bytes as a 'ByteString'. Fails if fewer than @n#@ bytes are
--   available.
--
-- Undefined behaviour if given a negative integer.
--
-- This does no copying. The 'B.ByteString' returned is a "slice" of the input,
-- and will keep it alive. To avoid this, use 'B.copy' on the output.
takeUnsafe# :: Int# -> ParserT st e B.ByteString
takeUnsafe# n# = ParserT \fp eob s st ->
    case n# <=# minusAddr# eob s of
      1# -> OK#   st (B.PS (ForeignPtr s fp) 0 (I# n#)) (plusAddr# s n#)
      _  -> Fail# st
{-# inline takeUnsafe# #-}

-- | Consume the rest of the input. May return the empty bytestring.
--
-- This does no copying. The 'B.ByteString' returned is a "slice" of the input,
-- and will keep it alive. To avoid this, use 'B.copy' on the output.
takeRest :: ParserT st e B.ByteString
takeRest = ParserT \fp eob s st ->
  let n# = minusAddr# eob s
  in  OK# st (B.PS (ForeignPtr s fp) 0 (I# n#)) eob
{-# inline takeRest #-}

-- | Skip forward @n@ bytes. Fails if fewer than @n@ bytes are available.
--
-- Throws a runtime error if given a negative integer.
skip :: Int -> ParserT st e ()
skip (I# n#) = skip# n#
{-# inline skip #-}

-- | Skip forward @n#@ bytes. Fails if fewer than @n#@ bytes are available.
--
-- Throws a runtime error if given a negative integer.
skip# :: Int# -> ParserT st e ()
skip# n# = atSkip# n# (pure ())
{-# inline skip# #-}

-- | Go back @i@ bytes in the input. Takes a positive integer.
--
-- Extremely unsafe. Makes no checks. Almost certainly a Bad Idea.
skipBack :: Int -> ParserT st e ()
skipBack = Common.withIntUnwrap# skipBack#
{-# inline skipBack #-}

-- | Go back @n#@ bytes. Takes a positive integer.
--
-- Extremely unsafe. Makes no checks. Almost certainly a Bad Idea.
skipBack# :: Int# -> ParserT st e ()
skipBack# n# = ParserT \fp eob s st ->
    OK# st () (plusAddr# s (negateInt# n#))
{-# inline skipBack# #-}

-- | Skip forward @n#@ bytes and run the given parser. Fails if fewer than @n#@
--   bytes are available.
--
-- Throws a runtime error if given a negative integer.
atSkip# :: Int# -> ParserT st e a -> ParserT st e a
atSkip# n# p = Common.withPosInt# n# (atSkipUnsafe# n# p)
{-# inline atSkip# #-}

-- | Skip forward @n@ bytes and run the given parser. Fails if fewer than @n@
--   bytes are available.
--
-- Undefined behaviour if given a negative integer.
atSkipUnsafe# :: Int# -> ParserT st e r -> ParserT st e r
atSkipUnsafe# n# (ParserT p) =
    withEnsure# n# $ ParserT \fp eob s st ->
        p fp eob (plusAddr# s n#) st
{-# inline atSkipUnsafe# #-}

--------------------------------------------------------------------------------

-- | Skip a parser zero or more times.
skipMany :: ParserT st e a -> ParserT st e ()
skipMany (ParserT f) = ParserT go where
  go fp eob s st = case f fp eob s st of
    OK# st a s -> go fp eob s st
    Fail# st   -> OK# st () s
    Err# st e  -> Err# st e
{-# inline skipMany #-}

-- TODO identical to one from parser-combinators
-- | Skip a parser one or more times.
skipSome :: ParserT st e a -> ParserT st e ()
skipSome p = p *> skipMany p
{-# inline skipSome #-}