{-|

This modules provides a pure haskell implementation of a reader and writer for
the ASCII HEPEVT file format.

-}
module Data.HEPEVT (
  Event,

  parseEventFile,
  parseEvents,
) where

import qualified Data.ByteString.Char8 as S

type Event = ([Double], [[Double]])

parseEventFile :: String -> IO [Event]
parseEventFile fname = do
  S.readFile fname >>= return . parseEvents fname

data Line = Meta String | E [Double] | P [Double] | V [Double] | Blank
  deriving (Show, Eq)

parseLine :: String -> Line
parseLine line =
  let ws = words line in
    parseLine' ws line
  where
    parseLine' ("E":xs) _ = E $ map parseDouble xs
    parseLine' ("P":xs) _ = P $ map parseDouble xs
    parseLine' ("V":xs) _ = V $ map parseDouble xs
    parseLine' _ line = if length line > 1 then Meta line else Blank

getLines :: [String] -> [Line]
getLines = map parseLine

type ParseState = [Event]

parseEvents :: String -> S.ByteString -> [Event]
parseEvents fname dat =
  let ls = S.split '\n' dat in 
    reverse $ foldl process [] $ getLines (map S.unpack ls)
  where
    process events (E ds) = (ds, []):events
    process ((el, vl):events) (V ds) = (el, ds:vl):events
    process events _ = events

parseDouble :: String -> Double
parseDouble = read . reverse . dropWhile (=='.') . reverse