module Minilang.Lambda.Parser where

import Control.Applicative (Alternative (many), (<|>))
import Data.Bifunctor (first)
import Data.Text (Text, pack)
import Data.Void (Void)
import Text.Megaparsec (Parsec, between, empty, errorBundlePretty, manyTill, notFollowedBy, optional, parse, try)
import Text.Megaparsec.Char (alphaNumChar, char, letterChar, space1, string, symbolChar)
import qualified Text.Megaparsec.Char.Lexer as L

type Parser = Parsec Void Text

data ParseError = ParseError Text
  deriving (Eq, Show)

data AST = Sym Text
  deriving (Eq, Show)

parse :: Text -> Either ParseError AST
parse =
  first (ParseError . pack . errorBundlePretty) . Text.Megaparsec.parse symbol ""

symbol :: Parser AST
symbol = Sym . pack <$> identifier

identifier :: Parser String
identifier =
  lexeme $
    (:)
      <$> (letterChar <|> extraChars)
      <*> many (alphaNumChar <|> extraChars)

lexeme :: Parser a -> Parser a
lexeme = L.lexeme spaceConsumer

extraChars :: Parser Char
extraChars =
  foldl (\b a -> char a <|> b) symbolChar extraIdentifierChars

initialChars :: [Char]
initialChars =
  ['a' .. 'z'] <> ['A' .. 'Z'] <> extraIdentifierChars

restChars :: [Char]
restChars =
  initialChars <> ['0' .. '9']

extraIdentifierChars :: String
extraIdentifierChars = ['-', '_', '*', '#', '%', '&', ':', '@', '/']

spaceConsumer :: Parser ()
spaceConsumer =
  L.space space1 (L.skipLineComment ";") empty