{-# LANGUAGE BangPatterns #-}
-- |
-- Module      : Data.Text.Lazy.Fusion
-- Copyright   : (c) 2009, 2010 Bryan O'Sullivan
--
-- License     : BSD-style
-- Maintainer  : bos@serpentine.com
-- Stability   : experimental
-- Portability : GHC
--
-- /Warning/: this is an internal module, and does not have a stable
-- API or name. Functions in this module may not check or enforce
-- preconditions expected by public modules. Use at your own risk!
--
-- Core stream fusion functionality for text.

module Data.Text.Internal.Lazy.Fusion
    (
      stream
    , unstream
    , unstreamChunks
    , length
    , unfoldrN
    , index
    , countChar
    ) where

import Prelude hiding (length)
import qualified Data.Text.Internal.Fusion.Common as S
import Control.Monad.ST (runST)
import Data.Text.Internal.Fusion.Types
import Data.Text.Internal.Fusion.Size (isEmpty, unknownSize)
import Data.Text.Internal.Lazy
import qualified Data.Text.Internal as I
import qualified Data.Text.Array as A
import Data.Text.Internal.Unsafe.Char (unsafeWrite)
import Data.Text.Internal.Unsafe.Shift (shiftL)
import Data.Text.Unsafe (Iter(..), iter)
import Data.Int (Int64)

default(Int64)

-- | /O(n)/ Convert a 'Text' into a 'Stream Char'.
stream :: Text -> Stream Char
stream text = Stream next (text :*: 0) unknownSize
  where
    next (Empty :*: _) = Done
    next (txt@(Chunk t@(I.Text _ _ len) ts) :*: i)
        | i >= len  = next (ts :*: 0)
        | otherwise = Yield c (txt :*: i+d)
        where Iter c d = iter t i
{-# INLINE [0] stream #-}

-- | /O(n)/ Convert a 'Stream Char' into a 'Text', using the given
-- chunk size.
unstreamChunks :: Int -> Stream Char -> Text
unstreamChunks !chunkSize (Stream next s0 len0)
  | isEmpty len0 = Empty
  | otherwise    = outer s0
  where
    outer so = {-# SCC "unstreamChunks/outer" #-}
              case next so of
                Done       -> Empty
                Skip s'    -> outer s'
                Yield x s' -> runST $ do
                                a <- A.new unknownLength
                                unsafeWrite a 0 x >>= inner a unknownLength s'
                    where unknownLength = 4
      where
        inner marr !len s !i
            | i + 1 >= chunkSize = finish marr i s
            | i + 1 >= len       = {-# SCC "unstreamChunks/resize" #-} do
                let newLen = min (len `shiftL` 1) chunkSize
                marr' <- A.new newLen
                A.copyM marr' 0 marr 0 len
                inner marr' newLen s i
            | otherwise =
                {-# SCC "unstreamChunks/inner" #-}
                case next s of
                  Done        -> finish marr i s
                  Skip s'     -> inner marr len s' i
                  Yield x s'  -> do d <- unsafeWrite marr i x
                                    inner marr len s' (i+d)
        finish marr len s' = do
          arr <- A.unsafeFreeze marr
          return (I.Text arr 0 len `Chunk` outer s')
{-# INLINE [0] unstreamChunks #-}

-- | /O(n)/ Convert a 'Stream Char' into a 'Text', using
-- 'defaultChunkSize'.
unstream :: Stream Char -> Text
unstream = unstreamChunks defaultChunkSize
{-# INLINE [0] unstream #-}

-- | /O(n)/ Returns the number of characters in a text.
length :: Stream Char -> Int64
length = S.lengthI
{-# INLINE[0] length #-}

{-# RULES "LAZY STREAM stream/unstream fusion" forall s.
    stream (unstream s) = s #-}

-- | /O(n)/ Like 'unfoldr', 'unfoldrN' builds a stream from a seed
-- value. However, the length of the result is limited by the
-- first argument to 'unfoldrN'. This function is more efficient than
-- 'unfoldr' when the length of the result is known.
unfoldrN :: Int64 -> (a -> Maybe (Char,a)) -> a -> Stream Char
unfoldrN n = S.unfoldrNI n
{-# INLINE [0] unfoldrN #-}

-- | /O(n)/ stream index (subscript) operator, starting from 0.
index :: Stream Char -> Int64 -> Char
index = S.indexI
{-# INLINE [0] index #-}

-- | /O(n)/ The 'count' function returns the number of times the query
-- element appears in the given stream.
countChar :: Char -> Stream Char -> Int64
countChar = S.countCharI
{-# INLINE [0] countChar #-}