{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# OPTIONS_HADDOCK prune not-home #-}

{- |
Module      : Data.Attoparsec.Framer.Testing
Copyright   : (c) 2022 Tim Emiola
Maintainer  : Tim Emiola <adetokunbo@emio.la>
SPDX-License-Identifier: BSD3

This module provides combinators that simplify unit tests of code that
use @'Framer's@.
-}
module Data.Attoparsec.Framer.Testing (
  -- * testing combinators
  parsesFromFramerOk,
  chunksOfN,
) where

import Control.Exception (catch)
import qualified Data.Attoparsec.ByteString as A
import Data.Attoparsec.Framer
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import Data.IORef (
  IORef,
  modifyIORef',
  newIORef,
  readIORef,
  writeIORef,
 )
import Data.List (unfoldr)
import Data.Word (Word32)


{- | Creates a 'Framer' and uses 'runFramer to confirm that the expect frames
  are received '
-}
parsesFromFramerOk :: Eq a => (a -> ByteString) -> A.Parser a -> Word32 -> [a] -> IO Bool
parsesFromFramerOk asBytes parser chunkSize' wanted = do
  chunkStore <- newIORef Nothing
  dst <- newIORef []
  let updateDst x = modifyIORef' dst ((:) x)
      mkChunks n = mconcat $ map (chunksOfN n . asBytes) wanted
      src = nextFrom' mkChunks chunkStore
      frames = setChunkSize chunkSize' $ mkFramer parser updateDst src
  runFramer frames `catch` (\(_e :: NoMoreInput) -> pure ())

  got <- readIORef dst
  pure $ got == reverse wanted


-- | Split a 'ByteString' into chunks of given size
chunksOfN :: Int -> ByteString -> [ByteString]
chunksOfN x b =
  let go y =
        let taken = BS.take x y
         in if BS.null taken then Nothing else Just (taken, BS.drop x y)
   in unfoldr go b


nextFrom' ::
  (Int -> [ByteString]) -> IORef (Maybe [ByteString]) -> Word32 -> IO ByteString
nextFrom' initChunks chunkStore chunkSize' = do
  readIORef chunkStore >>= \case
    Nothing -> do
      writeIORef chunkStore $ Just $ initChunks $ fromIntegral chunkSize'
      nextFrom' initChunks chunkStore chunkSize'
    Just [] -> pure BS.empty
    Just (x : xs) -> do
      writeIORef chunkStore $ Just xs
      pure x