module ParseBookfile where

import Control.Monad
import Data.Void
import Environment (Bookfile (..))
import Text.Megaparsec
import Text.Megaparsec.Char
import qualified Text.Megaparsec.Char.Lexer as L

-- use String, since we need FilePaths which are type aliases over String anyway.
type Parser = Parsec Void String

__VERSION__ :: Int
__VERSION__ = 2

parseMagicLine :: Parser Int
parseMagicLine = do
  void (char '%') <?> "first line to begin with % character"
  void spaceChar <?> "a space character"
  void (string "publish")
  void spaceChar <?> "a space character"
  void (char 'v') <?> "the character v and then a number"
  v <- L.decimal <?> "the bookfile schema version number"
  unless (v == __VERSION__) (fail ("currently recognized bookfile schema version is v" ++ show __VERSION__))
  void newline
  return v

parseBeginLine :: Parser ()
parseBeginLine = try $ label "begin marker" $ do
  void (string "% begin")
  void newline

parseFileLine :: Parser FilePath
parseFileLine = do
  notFollowedBy (char '%')
  file <- takeWhile1P (Just "line containing a filename") (/= '\n')
  return file

parseEndLine :: Parser ()
parseEndLine = try $ label "end marker" $ do
  void (string "% end")
  void newline

parseBlank :: Parser ()
parseBlank = do
  void (hidden (many newline))

parseBookfile :: Parser Bookfile
parseBookfile = do
  version <- parseMagicLine
  preambles <- many (parseBlank *> parseFileLine <* parseBlank)
  parseBeginLine
  fragments <- many (parseBlank *> parseFileLine <* parseBlank)
  parseEndLine
  trailers <- many (parseBlank *> parseFileLine <* parseBlank)
  return
    Bookfile
      { versionFrom = version,
        preamblesFrom = preambles,
        fragmentsFrom = fragments,
        trailersFrom = trailers
      }