{-# LANGUAGE OverloadedStrings #-}

module SimpleParser.Examples.Sexp
  ( Sexp (..)
  , SexpF (..)
  , Atom (..)
  , SexpLabel (..)
  , SexpParserC
  , SexpParserM
  , sexpParser
  , recSexpParser
  ) where

import Control.Monad (void)
import Data.Char (isDigit, isSpace)
import Data.Foldable (asum)
import Data.Scientific (Scientific)
import Data.Sequence (Seq)
import Data.Text (Text)
import Data.Void (Void)
import SimpleParser (Chunked (..), EmbedTextLabel (..), ExplainLabel (..), Parser, TextLabel, TextualStream,
                     betweenParser, commitParser, decimalParser, escapedStringParser, lexemeParser, matchToken,
                     onEmptyParser, orParser, packChunk, satisfyToken, scientificParser, sepByParser,
                     signedNumStartPred, signedParser, spaceParser, takeTokensWhile)

data Atom =
    AtomIdent !Text
  | AtomString !Text
  | AtomInt !Integer
  | AtomFloat !Scientific
  deriving (Eq, Show)

data SexpF a =
    SexpAtom !Atom
  | SexpList !(Seq a)
  deriving (Eq, Show, Functor, Foldable, Traversable)

data SexpLabel =
    SexpLabelIdentStart
  | SexpLabelEmbedText !TextLabel
  deriving (Eq, Show)

instance ExplainLabel SexpLabel where
  explainLabel sl =
    case sl of
      SexpLabelIdentStart -> "start of identifier"
      SexpLabelEmbedText tl -> explainLabel tl

instance EmbedTextLabel SexpLabel where
  embedTextLabel = SexpLabelEmbedText

newtype Sexp = Sexp { unSexp :: SexpF Sexp }
  deriving (Eq, Show)

type SexpParserC s = TextualStream s

type SexpParserM s a = Parser SexpLabel s Void a

sexpParser :: SexpParserC s => SexpParserM s Sexp
sexpParser = let p = fmap Sexp (recSexpParser p) in p

recSexpParser :: SexpParserC s => SexpParserM s a -> SexpParserM s (SexpF a)
recSexpParser root = onEmptyParser (orParser lp ap) (fail "failed to parse sexp document") where
  lp = commitParser openParenP (fmap SexpList (listP root))
  ap = fmap SexpAtom atomP

nonDelimPred :: Char -> Bool
nonDelimPred c = c /= '(' && c /= ')' && not (isSpace c)

identStartPred :: Char -> Bool
identStartPred c = not (isDigit c) && identContPred c

identContPred :: Char -> Bool
identContPred c = c /= '"' && nonDelimPred c

stringP :: SexpParserC s => SexpParserM s Text
stringP = fmap packChunk (escapedStringParser '"')

identifierP :: SexpParserC s => SexpParserM s Text
identifierP = do
  x <- satisfyToken (Just SexpLabelIdentStart) identStartPred
  xs <- takeTokensWhile identContPred
  pure (packChunk (consChunk x xs))

spaceP :: SexpParserC s => SexpParserM s ()
spaceP = spaceParser

lexP :: SexpParserC s => SexpParserM s a -> SexpParserM s a
lexP = lexemeParser spaceP

openParenP :: SexpParserC s => SexpParserM s ()
openParenP = lexP (void (matchToken '('))

closeParenP :: SexpParserC s => SexpParserM s ()
closeParenP = lexP (void (matchToken ')'))

intP :: SexpParserC s => SexpParserM s Integer
intP = signedParser (pure ()) decimalParser

floatP :: SexpParserC s => SexpParserM s Scientific
floatP = signedParser (pure ()) scientificParser

atomP :: SexpParserC s => SexpParserM s Atom
atomP = lexP $ asum
  [ commitParser (void (matchToken '"')) (fmap AtomString stringP)
  , commitParser (void (satisfyToken Nothing signedNumStartPred)) (fmap AtomInt intP)
  , commitParser (void (satisfyToken Nothing signedNumStartPred)) (fmap AtomFloat floatP)
  , commitParser (void (satisfyToken Nothing identStartPred)) (fmap AtomIdent identifierP)
  ]

listP :: SexpParserC s => SexpParserM s a -> SexpParserM s (Seq a)
listP root = lexP (betweenParser openParenP closeParenP (sepByParser root spaceP))