{-# LANGUAGE ViewPatterns #-}

module Formats.Scale where

import           Data.Sequence (Seq)
import qualified Data.Sequence as S
import           Data.Text (Text)
import qualified Data.Text as T

import           State (Note(..))

parse :: Text -> Either String (Seq Note)
parse t = case T.lines t of
  ((T.takeWhile (/= '#') -> "hypsibius scale"):rs) -> parseLines rs
  _ -> Left "Not a valid Hypsibius scale: missing header\n"

parseLines :: [Text] -> Either String (Seq Note)
parseLines [] = pure S.empty
parseLines (l:ls) =
  case T.words (T.takeWhile (/= '#') l) of
    [] -> parseLines ls
    [cents, name] ->
      let n = Note (read (T.unpack cents)) name
      in (n S.<|) <$> parseLines ls
    rs -> Left ("Bad declaration: " ++ show rs)