{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
{-# OPTIONS_HADDOCK prune #-}
{-# LANGUAGE Trustworthy #-}

-- |
-- Module      : Data.ByteString.Lazy
-- Copyright   : (c) Don Stewart 2006
--               (c) Duncan Coutts 2006-2011
-- License     : BSD-style
--
-- Maintainer  : dons00@gmail.com, duncan@community.haskell.org
-- Stability   : stable
-- Portability : portable
--
-- A time and space-efficient implementation of lazy byte vectors
-- using lists of packed 'Word8' arrays, suitable for high performance
-- use, both in terms of large data quantities, or high speed
-- requirements. Lazy ByteStrings are encoded as lazy lists of strict chunks
-- of bytes.
--
-- A key feature of lazy ByteStrings is the means to manipulate large or
-- unbounded streams of data without requiring the entire sequence to be
-- resident in memory. To take advantage of this you have to write your
-- functions in a lazy streaming style, e.g. classic pipeline composition. The
-- default I\/O chunk size is 32k, which should be good in most circumstances.
--
-- Some operations, such as 'concat', 'append', 'reverse' and 'cons', have
-- better complexity than their "Data.ByteString" equivalents, due to
-- optimisations resulting from the list spine structure. For other
-- operations lazy ByteStrings are usually within a few percent of
-- strict ones.
--
-- The recomended way to assemble lazy ByteStrings from smaller parts
-- is to use the builder monoid from "Data.ByteString.Builder".
--
-- This module is intended to be imported @qualified@, to avoid name
-- clashes with "Prelude" functions.  eg.
--
-- > import qualified Data.ByteString.Lazy as B
--
-- Original GHC implementation by Bryan O\'Sullivan.
-- Rewritten to use 'Data.Array.Unboxed.UArray' by Simon Marlow.
-- Rewritten to support slices and use 'Foreign.ForeignPtr.ForeignPtr'
-- by David Roundy.
-- Rewritten again and extended by Don Stewart and Duncan Coutts.
-- Lazy variant by Duncan Coutts and Don Stewart.
--

module Data.ByteString.Lazy (

        -- * Lazy @ByteString@
        ByteString,
        LazyByteString,

        -- * Introducing and eliminating 'ByteString's
        empty,
        singleton,
        pack,
        unpack,
        fromStrict,
        toStrict,
        fromChunks,
        toChunks,
        foldrChunks,
        foldlChunks,

        -- * Basic interface
        cons,
        cons',
        snoc,
        append,
        head,
        uncons,
        unsnoc,
        last,
        tail,
        init,
        null,
        length,

        -- * Transforming ByteStrings
        map,
        reverse,
        intersperse,
        intercalate,
        transpose,

        -- * Reducing 'ByteString's (folds)
        foldl,
        foldl',
        foldl1,
        foldl1',
        foldr,
        foldr',
        foldr1,
        foldr1',

        -- ** Special folds
        concat,
        concatMap,
        any,
        all,
        maximum,
        minimum,
        compareLength,

        -- * Building ByteStrings
        -- ** Scans
        scanl,
        scanl1,
        scanr,
        scanr1,

        -- ** Accumulating maps
        mapAccumL,
        mapAccumR,

        -- ** Infinite ByteStrings
        repeat,
        replicate,
        cycle,
        iterate,

        -- ** Unfolding ByteStrings
        unfoldr,

        -- * Substrings

        -- ** Breaking strings
        take,
        takeEnd,
        drop,
        dropEnd,
        splitAt,
        takeWhile,
        takeWhileEnd,
        dropWhile,
        dropWhileEnd,
        span,
        spanEnd,
        break,
        breakEnd,
        group,
        groupBy,
        inits,
        tails,
        stripPrefix,
        stripSuffix,

        -- ** Breaking into many substrings
        split,
        splitWith,

        -- * Predicates
        isPrefixOf,
        isSuffixOf,
--        isInfixOf,

        -- ** Search for arbitrary substrings
--        isSubstringOf,

        -- * Searching ByteStrings

        -- ** Searching by equality
        elem,
        notElem,

        -- ** Searching with a predicate
        find,
        filter,
        partition,

        -- * Indexing ByteStrings
        index,
        indexMaybe,
        (!?),
        elemIndex,
        elemIndexEnd,
        elemIndices,
        findIndex,
        findIndexEnd,
        findIndices,
        count,

        -- * Zipping and unzipping ByteStrings
        zip,
        zipWith,
        packZipWith,
        unzip,

        -- * Ordered ByteStrings
--        sort,

        -- * Low level conversions
        -- ** Copying ByteStrings
        copy,
--        defrag,

        -- * I\/O with 'ByteString's
        -- $IOChunk

        -- ** Standard input and output
        getContents,
        putStr,
        interact,

        -- ** Files
        readFile,
        writeFile,
        appendFile,

        -- ** I\/O with Handles
        hGetContents,
        hGet,
        hGetNonBlocking,
        hPut,
        hPutNonBlocking,
        hPutStr,

  ) where

import Prelude hiding
    (reverse,head,tail,last,init,null,length,map,lines,foldl,foldr,unlines
    ,concat,any,take,drop,splitAt,takeWhile,dropWhile,span,break,elem,filter,maximum
    ,minimum,all,concatMap,foldl1,foldr1,scanl, scanl1, scanr, scanr1
    ,repeat, cycle, interact, iterate,readFile,writeFile,appendFile,replicate
    ,getContents,getLine,putStr,putStrLn ,zip,zipWith,unzip,notElem)

import qualified Data.List              as List
import qualified Data.Bifunctor         as BF
import qualified Data.ByteString        as P  (ByteString) -- type name only
import qualified Data.ByteString        as S  -- S for strict (hmm...)
import qualified Data.ByteString.Internal as S
import qualified Data.ByteString.Unsafe as S
import qualified Data.ByteString.Lazy.Internal.Deque as D
import Data.ByteString.Lazy.Internal

import Control.Monad            (mplus)
import Data.Word                (Word8)
import Data.Int                 (Int64)
import GHC.Stack.Types          (HasCallStack)
import System.IO                (Handle,openBinaryFile,stdin,stdout,withBinaryFile,IOMode(..)
                                ,hClose)
import System.IO.Error          (mkIOError, illegalOperationErrorType)
import System.IO.Unsafe

import Foreign.Ptr
import Foreign.Storable


-- -----------------------------------------------------------------------------
-- Introducing and eliminating 'ByteString's

-- | /O(1)/ The empty 'ByteString'
empty :: ByteString
empty = Empty
{-# INLINE empty #-}

-- | /O(1)/ Convert a 'Word8' into a 'ByteString'
singleton :: Word8 -> ByteString
singleton w = Chunk (S.singleton w) Empty
{-# INLINE singleton #-}

-- | /O(n)/ Convert a '[Word8]' into a 'ByteString'.
pack :: [Word8] -> ByteString
pack = packBytes

-- | /O(n)/ Converts a 'ByteString' to a '[Word8]'.
unpack :: ByteString -> [Word8]
unpack = unpackBytes

-- | /O(c)/ Convert a list of strict 'ByteString' into a lazy 'ByteString'
fromChunks :: [P.ByteString] -> ByteString
fromChunks = List.foldr chunk Empty

-- | /O(c)/ Convert a lazy 'ByteString' into a list of strict 'ByteString'
toChunks :: ByteString -> [P.ByteString]
toChunks = foldrChunks (:) []

------------------------------------------------------------------------

{-
-- | /O(n)/ Convert a '[a]' into a 'ByteString' using some
-- conversion function
packWith :: (a -> Word8) -> [a] -> ByteString
packWith k str = LPS $ L.map (P.packWith k) (chunk defaultChunkSize str)
{-# INLINE packWith #-}
{-# SPECIALIZE packWith :: (Char -> Word8) -> [Char] -> ByteString #-}

-- | /O(n)/ Converts a 'ByteString' to a '[a]', using a conversion function.
unpackWith :: (Word8 -> a) -> ByteString -> [a]
unpackWith k (LPS ss) = L.concatMap (S.unpackWith k) ss
{-# INLINE unpackWith #-}
{-# SPECIALIZE unpackWith :: (Word8 -> Char) -> ByteString -> [Char] #-}
-}

-- ---------------------------------------------------------------------
-- Basic interface

-- | /O(1)/ Test whether a ByteString is empty.
null :: ByteString -> Bool
null Empty = True
null _     = False
{-# INLINE null #-}

-- | /O(c)/ 'length' returns the length of a ByteString as an 'Int64'
length :: ByteString -> Int64
length = foldlChunks (\n c -> n + fromIntegral (S.length c)) 0
{-# INLINE [1] length #-}

infixr 5 `cons`, `cons'` --same as list (:)
infixl 5 `snoc`

-- | /O(1)/ 'cons' is analogous to '(Prelude.:)' for lists.
--
cons :: Word8 -> ByteString -> ByteString
cons c = Chunk (S.singleton c)
{-# INLINE cons #-}

-- | /O(1)/ Unlike 'cons', 'cons'' is
-- strict in the ByteString that we are consing onto. More precisely, it forces
-- the head and the first chunk. It does this because, for space efficiency, it
-- may coalesce the new byte onto the first \'chunk\' rather than starting a
-- new \'chunk\'.
--
-- So that means you can't use a lazy recursive contruction like this:
--
-- > let xs = cons' c xs in xs
--
-- You can however use 'cons', as well as 'repeat' and 'cycle', to build
-- infinite lazy ByteStrings.
--
cons' :: Word8 -> ByteString -> ByteString
cons' w (Chunk c cs) | S.length c < 16 = Chunk (S.cons w c) cs
cons' w cs                             = Chunk (S.singleton w) cs
{-# INLINE cons' #-}

-- | /O(n\/c)/ Append a byte to the end of a 'ByteString'
snoc :: ByteString -> Word8 -> ByteString
snoc cs w = foldrChunks Chunk (singleton w) cs
{-# INLINE snoc #-}

-- | /O(1)/ Extract the first element of a ByteString, which must be non-empty.
head :: HasCallStack => ByteString -> Word8
head Empty       = errorEmptyList "head"
head (Chunk c _) = S.unsafeHead c
{-# INLINE head #-}

-- | /O(1)/ Extract the head and tail of a ByteString, returning Nothing
-- if it is empty.
uncons :: ByteString -> Maybe (Word8, ByteString)
uncons Empty = Nothing
uncons (Chunk c cs)
    = Just (S.unsafeHead c,
            if S.length c == 1 then cs else Chunk (S.unsafeTail c) cs)
{-# INLINE uncons #-}

-- | /O(1)/ Extract the elements after the head of a ByteString, which must be
-- non-empty.
tail :: HasCallStack => ByteString -> ByteString
tail Empty          = errorEmptyList "tail"
tail (Chunk c cs)
  | S.length c == 1 = cs
  | otherwise       = Chunk (S.unsafeTail c) cs
{-# INLINE tail #-}

-- | /O(n\/c)/ Extract the last element of a ByteString, which must be finite
-- and non-empty.
last :: HasCallStack => ByteString -> Word8
last Empty          = errorEmptyList "last"
last (Chunk c0 cs0) = go c0 cs0
  where go c Empty        = S.unsafeLast c
        go _ (Chunk c cs) = go c cs
-- XXX Don't inline this. Something breaks with 6.8.2 (haven't investigated yet)

-- | /O(n\/c)/ Return all the elements of a 'ByteString' except the last one.
init :: HasCallStack => ByteString -> ByteString
init Empty          = errorEmptyList "init"
init (Chunk c0 cs0) = go c0 cs0
  where go c Empty | S.length c == 1 = Empty
                   | otherwise       = Chunk (S.unsafeInit c) Empty
        go c (Chunk c' cs)           = Chunk c (go c' cs)

-- | /O(n\/c)/ Extract the 'init' and 'last' of a ByteString, returning Nothing
-- if it is empty.
--
-- * It is no faster than using 'init' and 'last'
unsnoc :: ByteString -> Maybe (ByteString, Word8)
unsnoc Empty        = Nothing
unsnoc (Chunk c cs) = Just (init (Chunk c cs), last (Chunk c cs))

-- | /O(n\/c)/ Append two ByteStrings
append :: ByteString -> ByteString -> ByteString
append = mappend
{-# INLINE append #-}

-- ---------------------------------------------------------------------
-- Transformations

-- | /O(n)/ 'map' @f xs@ is the ByteString obtained by applying @f@ to each
-- element of @xs@.
map :: (Word8 -> Word8) -> ByteString -> ByteString
map f = go
    where
        go Empty        = Empty
        go (Chunk x xs) = Chunk y ys
            where
                y  = S.map f x
                ys = go xs
{-# INLINE map #-}

-- | /O(n)/ 'reverse' @xs@ returns the elements of @xs@ in reverse order.
reverse :: ByteString -> ByteString
reverse = rev Empty
  where rev a Empty        = a
        rev a (Chunk c cs) = rev (Chunk (S.reverse c) a) cs
{-# INLINE reverse #-}

-- | The 'intersperse' function takes a 'Word8' and a 'ByteString' and
-- \`intersperses\' that byte between the elements of the 'ByteString'.
-- It is analogous to the intersperse function on Lists.
intersperse :: Word8 -> ByteString -> ByteString
intersperse _ Empty        = Empty
intersperse w (Chunk c cs) = Chunk (S.intersperse w c)
                                   (foldrChunks (Chunk . intersperse') Empty cs)
  where intersperse' :: P.ByteString -> P.ByteString
        intersperse' (S.BS fp l) =
          S.unsafeCreate (2*l) $ \p' -> S.unsafeWithForeignPtr fp $ \p -> do
            poke p' w
            S.c_intersperse (p' `plusPtr` 1) p (fromIntegral l) w

-- | The 'transpose' function transposes the rows and columns of its
-- 'ByteString' argument.
transpose :: [ByteString] -> [ByteString]
transpose css = List.map (\ss -> Chunk (S.pack ss) Empty)
                      (List.transpose (List.map unpack css))
--TODO: make this fast

-- ---------------------------------------------------------------------
-- Reducing 'ByteString's

-- | 'foldl', applied to a binary operator, a starting value (typically
-- the left-identity of the operator), and a ByteString, reduces the
-- ByteString using the binary operator, from left to right.
foldl :: (a -> Word8 -> a) -> a -> ByteString -> a
foldl f = go
  where go a Empty        = a
        go a (Chunk c cs) = go (S.foldl f a c) cs
{-# INLINE foldl #-}

-- | 'foldl'' is like 'foldl', but strict in the accumulator.
foldl' :: (a -> Word8 -> a) -> a -> ByteString -> a
foldl' f = go
  where go !a Empty        = a
        go !a (Chunk c cs) = go (S.foldl' f a c) cs
{-# INLINE foldl' #-}

-- | 'foldr', applied to a binary operator, a starting value
-- (typically the right-identity of the operator), and a ByteString,
-- reduces the ByteString using the binary operator, from right to left.
foldr :: (Word8 -> a -> a) -> a -> ByteString -> a
foldr k = foldrChunks (flip (S.foldr k))
{-# INLINE foldr #-}

-- | 'foldr'' is like 'foldr', but strict in the accumulator.
--
-- @since 0.11.2.0
foldr' :: (Word8 -> a -> a) -> a -> ByteString -> a
foldr' f a = go
  where
    go Empty = a
    go (Chunk c cs) = S.foldr' f (foldr' f a cs) c
{-# INLINE foldr' #-}

-- | 'foldl1' is a variant of 'foldl' that has no starting value
-- argument, and thus must be applied to non-empty 'ByteString's.
foldl1 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
foldl1 _ Empty        = errorEmptyList "foldl1"
foldl1 f (Chunk c cs) = foldl f (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)

-- | 'foldl1'' is like 'foldl1', but strict in the accumulator.
foldl1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
foldl1' _ Empty        = errorEmptyList "foldl1'"
foldl1' f (Chunk c cs) = foldl' f (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)

-- | 'foldr1' is a variant of 'foldr' that has no starting value argument,
-- and thus must be applied to non-empty 'ByteString's
foldr1 :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
foldr1 _ Empty          = errorEmptyList "foldr1"
foldr1 f (Chunk c0 cs0) = go c0 cs0
  where go c Empty         = S.foldr1 f c
        go c (Chunk c' cs) = S.foldr  f (go c' cs) c

-- | 'foldr1'' is like 'foldr1', but strict in the accumulator.
--
-- @since 0.11.2.0
foldr1' :: HasCallStack => (Word8 -> Word8 -> Word8) -> ByteString -> Word8
foldr1' _ Empty          = errorEmptyList "foldr1'"
foldr1' f (Chunk c0 cs0) = go c0 cs0
  where go c Empty         = S.foldr1' f c
        go c (Chunk c' cs) = S.foldr'  f (go c' cs) c

-- ---------------------------------------------------------------------
-- Special folds

-- | /O(n)/ Concatenate a list of ByteStrings.
concat :: [ByteString] -> ByteString
concat = mconcat

-- | Map a function over a 'ByteString' and concatenate the results
concatMap :: (Word8 -> ByteString) -> ByteString -> ByteString
concatMap _ Empty        = Empty
concatMap f (Chunk c0 cs0) = to c0 cs0
  where
    go :: ByteString -> P.ByteString -> ByteString -> ByteString
    go Empty        c' cs' = to c' cs'
    go (Chunk c cs) c' cs' = Chunk c (go cs c' cs')

    to :: P.ByteString -> ByteString -> ByteString
    to c cs | S.null c  = case cs of
        Empty          -> Empty
        (Chunk c' cs') -> to c' cs'
            | otherwise = go (f (S.unsafeHead c)) (S.unsafeTail c) cs

-- | /O(n)/ Applied to a predicate and a ByteString, 'any' determines if
-- any element of the 'ByteString' satisfies the predicate.
any :: (Word8 -> Bool) -> ByteString -> Bool
any f = foldrChunks (\c rest -> S.any f c || rest) False
{-# INLINE any #-}

-- | /O(n)/ Applied to a predicate and a 'ByteString', 'all' determines
-- if all elements of the 'ByteString' satisfy the predicate.
all :: (Word8 -> Bool) -> ByteString -> Bool
all f = foldrChunks (\c rest -> S.all f c && rest) True
{-# INLINE all #-}

-- | /O(n)/ 'maximum' returns the maximum value from a 'ByteString'
maximum :: HasCallStack => ByteString -> Word8
maximum Empty        = errorEmptyList "maximum"
maximum (Chunk c cs) = foldlChunks (\n c' -> n `max` S.maximum c')
                                   (S.maximum c) cs
{-# INLINE maximum #-}

-- | /O(n)/ 'minimum' returns the minimum value from a 'ByteString'
minimum :: HasCallStack => ByteString -> Word8
minimum Empty        = errorEmptyList "minimum"
minimum (Chunk c cs) = foldlChunks (\n c' -> n `min` S.minimum c')
                                     (S.minimum c) cs
{-# INLINE minimum #-}

-- | /O(c)/ 'compareLength' compares the length of a 'ByteString'
-- to an 'Int64'
--
-- @since 0.11.1.0
compareLength :: ByteString -> Int64 -> Ordering
compareLength _ toCmp | toCmp < 0 = GT
compareLength Empty toCmp         = compare 0 toCmp
compareLength (Chunk c cs) toCmp  = compareLength cs (toCmp - fromIntegral (S.length c))
{-# INLINE compareLength #-}

{-# RULES
"ByteString.Lazy length/compareN -> compareLength" [~1] forall t n.
  compare (length t) n = compareLength t n
"ByteString.Lazy compareN/length -> compareLength" [~1] forall t n.
  -- compare EQ LT = GT and vice versa
  compare n (length t) = compare EQ $ compareLength t n
"ByteString.Lazy length/==N -> compareLength/==EQ" [~1] forall t n.
   length t == n = compareLength t n == EQ
"ByteString.Lazy N==/length -> compareLength/==EQ" [~1] forall t n.
   n == length t = compareLength t n == EQ
"ByteString.Lazy length//=N -> compareLength//=EQ" [~1] forall t n.
   length t /= n = compareLength t n /= EQ
"ByteString.Lazy N/=/length -> compareLength//=EQ" [~1] forall t n.
   n /= length t = compareLength t n /= EQ
"ByteString.Lazy length/<N -> compareLength/==LT" [~1] forall t n.
   length t < n = compareLength t n == LT
"ByteString.Lazy >N/length -> compareLength/==LT" [~1] forall t n.
   n > length t = compareLength t n == LT
"ByteString.Lazy length/<=N -> compareLength//=GT" [~1] forall t n.
   length t <= n = compareLength t n /= GT
"ByteString.Lazy <=N/length -> compareLength//=GT" [~1] forall t n.
   n >= length t = compareLength t n /= GT
"ByteString.Lazy length/>N -> compareLength/==GT" [~1] forall t n.
   length t > n = compareLength t n == GT
"ByteString.Lazy <N/length -> compareLength/==GT" [~1] forall t n.
   n < length t = compareLength t n == GT
"ByteString.Lazy length/>=N -> compareLength//=LT" [~1] forall t n.
   length t >= n = compareLength t n /= LT
"ByteString.Lazy >=N/length -> compareLength//=LT" [~1] forall t n.
   n <= length t = compareLength t n /= LT
  #-}

-- | The 'mapAccumL' function behaves like a combination of 'map' and
-- 'foldl'; it applies a function to each element of a ByteString,
-- passing an accumulating parameter from left to right, and returning a
-- final value of this accumulator together with the new ByteString.
mapAccumL :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
mapAccumL f = go
  where
    go s Empty        = (s, Empty)
    go s (Chunk c cs) = (s'', Chunk c' cs')
        where (s',  c')  = S.mapAccumL f s c
              (s'', cs') = go s' cs

-- | The 'mapAccumR' function behaves like a combination of 'map' and
-- 'foldr'; it applies a function to each element of a ByteString,
-- passing an accumulating parameter from right to left, and returning a
-- final value of this accumulator together with the new ByteString.
mapAccumR :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
mapAccumR f = go
  where
    go s Empty        = (s, Empty)
    go s (Chunk c cs) = (s'', Chunk c' cs')
        where (s'', c') = S.mapAccumR f s' c
              (s', cs') = go s cs

-- ---------------------------------------------------------------------
-- Building ByteStrings

-- | 'scanl' is similar to 'foldl', but returns a list of successive
-- reduced values from the left.
--
-- > scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
--
-- Note that
--
-- > head (scanl f z xs) == z
-- > last (scanl f z xs) == foldl f z xs
--
scanl
    :: (Word8 -> Word8 -> Word8)
    -- ^ accumulator -> element -> new accumulator
    -> Word8
    -- ^ starting value of accumulator
    -> ByteString
    -- ^ input of length n
    -> ByteString
    -- ^ output of length n+1
scanl function = fmap (uncurry (flip snoc)) . mapAccumL (\x y -> (function x y, x))
{-# INLINE scanl #-}

-- | 'scanl1' is a variant of 'scanl' that has no starting value argument.
--
-- > scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
--
-- @since 0.11.2.0
scanl1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString
scanl1 function byteStream = case uncons byteStream of
  Nothing -> Empty
  Just (firstByte, remainingBytes) -> scanl function firstByte remainingBytes

-- | 'scanr' is similar to 'foldr', but returns a list of successive
-- reduced values from the right.
--
-- > scanr f z [..., x{n-1}, xn] == [..., x{n-1} `f` (xn `f` z), xn `f` z, z]
--
-- Note that
--
-- > head (scanr f z xs) == foldr f z xs
-- > last (scanr f z xs) == z
--
-- @since 0.11.2.0
scanr
    :: (Word8 -> Word8 -> Word8)
    -- ^ element -> accumulator -> new accumulator
    -> Word8
    -- ^ starting value of accumulator
    -> ByteString
    -- ^ input of length n
    -> ByteString
    -- ^ output of length n+1
scanr function = fmap (uncurry cons) . mapAccumR (\x y -> (function y x, x))

-- | 'scanr1' is a variant of 'scanr' that has no starting value argument.
--
-- @since 0.11.2.0
scanr1 :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString
scanr1 function byteStream = case unsnoc byteStream of
  Nothing -> Empty
  Just (initialBytes, lastByte) -> scanr function lastByte initialBytes

-- ---------------------------------------------------------------------
-- Unfolds and replicates

-- | @'iterate' f x@ returns an infinite ByteString of repeated applications
-- of @f@ to @x@:
--
-- > iterate f x == [x, f x, f (f x), ...]
--
iterate :: (Word8 -> Word8) -> Word8 -> ByteString
iterate f = unfoldr (\x -> case f x of !x' -> Just (x', x'))

-- | @'repeat' x@ is an infinite ByteString, with @x@ the value of every
-- element.
--
repeat :: Word8 -> ByteString
repeat w = cs where cs = Chunk (S.replicate smallChunkSize w) cs

-- | /O(n)/ @'replicate' n x@ is a ByteString of length @n@ with @x@
-- the value of every element.
--
replicate :: Int64 -> Word8 -> ByteString
replicate n w
    | n <= 0             = Empty
    | n < fromIntegral smallChunkSize = Chunk (S.replicate (fromIntegral n) w) Empty
    | r == 0             = cs -- preserve invariant
    | otherwise          = Chunk (S.unsafeTake (fromIntegral r) c) cs
 where
    c      = S.replicate smallChunkSize w
    cs     = nChunks q
    (q, r) = quotRem n (fromIntegral smallChunkSize)
    nChunks 0 = Empty
    nChunks m = Chunk c (nChunks (m-1))

-- | 'cycle' ties a finite ByteString into a circular one, or equivalently,
-- the infinite repetition of the original ByteString.
--
cycle :: HasCallStack => ByteString -> ByteString
cycle Empty = errorEmptyList "cycle"
cycle cs    = cs' where cs' = foldrChunks Chunk cs' cs

-- | /O(n)/ The 'unfoldr' function is analogous to the List \'unfoldr\'.
-- 'unfoldr' builds a ByteString from a seed value.  The function takes
-- the element and returns 'Nothing' if it is done producing the
-- ByteString or returns 'Just' @(a,b)@, in which case, @a@ is a
-- prepending to the ByteString and @b@ is used as the next element in a
-- recursive call.
unfoldr :: (a -> Maybe (Word8, a)) -> a -> ByteString
unfoldr f = unfoldChunk 32
  where unfoldChunk n x =
          case S.unfoldrN n f x of
            (c, Nothing)
              | S.null c  -> Empty
              | otherwise -> Chunk c Empty
            (c, Just x')  -> Chunk c (unfoldChunk (n*2) x')

-- ---------------------------------------------------------------------
-- Substrings

-- | /O(n\/c)/ 'take' @n@, applied to a ByteString @xs@, returns the prefix
-- of @xs@ of length @n@, or @xs@ itself if @n > 'length' xs@.
take :: Int64 -> ByteString -> ByteString
take i _ | i <= 0 = Empty
take i cs0         = take' i cs0
  where take' 0 _            = Empty
        take' _ Empty        = Empty
        take' n (Chunk c cs) =
          if n < fromIntegral (S.length c)
            then Chunk (S.take (fromIntegral n) c) Empty
            else Chunk c (take' (n - fromIntegral (S.length c)) cs)

-- | /O(c)/ @'takeEnd' n xs@ is equivalent to @'drop' ('length' xs - n) xs@.
-- Takes @n@ elements from end of bytestring.
--
-- >>> takeEnd 3 "abcdefg"
-- "efg"
-- >>> takeEnd 0 "abcdefg"
-- ""
-- >>> takeEnd 4 "abc"
-- "abc"
--
-- @since 0.11.2.0
takeEnd :: Int64 -> ByteString -> ByteString
takeEnd i _ | i <= 0 = Empty
takeEnd i cs0        = takeEnd' i cs0
  where takeEnd' 0 _         = Empty
        takeEnd' n cs        =
            snd $ foldrChunks takeTuple (n,Empty) cs
        takeTuple _ (0, cs)  = (0, cs)
        takeTuple c (n, cs)
            | n > fromIntegral (S.length c) = (n - fromIntegral (S.length c), Chunk c cs)
            | otherwise      = (0, Chunk (S.takeEnd (fromIntegral n) c) cs)

-- | /O(n\/c)/ 'drop' @n xs@ returns the suffix of @xs@ after the first @n@
-- elements, or @[]@ if @n > 'length' xs@.
drop  :: Int64 -> ByteString -> ByteString
drop i p | i <= 0 = p
drop i cs0 = drop' i cs0
  where drop' 0 cs           = cs
        drop' _ Empty        = Empty
        drop' n (Chunk c cs) =
          if n < fromIntegral (S.length c)
            then Chunk (S.drop (fromIntegral n) c) cs
            else drop' (n - fromIntegral (S.length c)) cs

-- | /O(n)/ @'dropEnd' n xs@ is equivalent to @'take' ('length' xs - n) xs@.
-- Drops @n@ elements from end of bytestring.
--
-- >>> dropEnd 3 "abcdefg"
-- "abcd"
-- >>> dropEnd 0 "abcdefg"
-- "abcdefg"
-- >>> dropEnd 4 "abc"
-- ""
--
-- @since 0.11.2.0
dropEnd :: Int64 -> ByteString -> ByteString
dropEnd i p | i <= 0 = p
dropEnd i p          = go D.empty p
  where go :: D.Deque -> ByteString -> ByteString
        go deque (Chunk c cs)
            | D.byteLength deque < i = go (D.snoc c deque) cs
            | otherwise              =
                  let (output, deque') = getOutput empty (D.snoc c deque)
                    in foldrChunks Chunk (go deque' cs) output
        go deque Empty               = fromDeque $ dropEndBytes deque i

        len c = fromIntegral (S.length c)

        -- get a `ByteString` from all the front chunks of the accumulating deque
        -- for which we know they won't be dropped
        getOutput :: ByteString -> D.Deque -> (ByteString, D.Deque)
        getOutput out deque = case D.popFront deque of
            Nothing                       -> (reverseChunks out, deque)
            Just (x, deque') | D.byteLength deque' >= i ->
                            getOutput (Chunk x out) deque'
            _ -> (reverseChunks out, deque)

        -- reverse a `ByteString`s chunks, keeping all internal `S.ByteString`s
        -- unchanged
        reverseChunks = foldlChunks (flip Chunk) empty

        -- drop n elements from the rear of the accumulating `deque`
        dropEndBytes :: D.Deque -> Int64 -> D.Deque
        dropEndBytes deque n = case D.popRear deque of
            Nothing                       -> deque
            Just (deque', x) | len x <= n -> dropEndBytes deque' (n - len x)
                             | otherwise  ->
                                D.snoc (S.dropEnd (fromIntegral n) x) deque'

        -- build a lazy ByteString from an accumulating `deque`
        fromDeque :: D.Deque -> ByteString
        fromDeque deque =
            List.foldr chunk Empty (D.front deque) `append`
            List.foldl' (flip chunk) Empty (D.rear deque)

-- | /O(n\/c)/ 'splitAt' @n xs@ is equivalent to @('take' n xs, 'drop' n xs)@.
splitAt :: Int64 -> ByteString -> (ByteString, ByteString)
splitAt i cs0 | i <= 0 = (Empty, cs0)
splitAt i cs0 = splitAt' i cs0
  where splitAt' 0 cs           = (Empty, cs)
        splitAt' _ Empty        = (Empty, Empty)
        splitAt' n (Chunk c cs) =
          if n < fromIntegral (S.length c)
            then (Chunk (S.take (fromIntegral n) c) Empty
                 ,Chunk (S.drop (fromIntegral n) c) cs)
            else let (cs', cs'') = splitAt' (n - fromIntegral (S.length c)) cs
                   in (Chunk c cs', cs'')


-- | Similar to 'P.takeWhile',
-- returns the longest (possibly empty) prefix of elements
-- satisfying the predicate.
takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
takeWhile f = takeWhile'
  where takeWhile' Empty        = Empty
        takeWhile' (Chunk c cs) =
          case S.findIndexOrLength (not . f) c of
            0                  -> Empty
            n | n < S.length c -> Chunk (S.take n c) Empty
              | otherwise      -> Chunk c (takeWhile' cs)

-- | Returns the longest (possibly empty) suffix of elements
-- satisfying the predicate.
--
-- @'takeWhileEnd' p@ is equivalent to @'reverse' . 'takeWhile' p . 'reverse'@.
--
-- >>> {-# LANGUAGE OverloadedLists #-)
-- >>> takeWhileEnd even [1,2,3,4,6]
-- [4,6]
--
-- @since 0.11.2.0
takeWhileEnd :: (Word8 -> Bool) -> ByteString -> ByteString
takeWhileEnd f = takeWhileEnd'
  where takeWhileEnd' Empty = Empty
        takeWhileEnd' cs    =
            snd $ foldrChunks takeTuple (True,Empty) cs
        takeTuple _ (False, bs) = (False,bs)
        takeTuple c (True,bs)   =
           case S.takeWhileEnd f c of
                c' | S.length c' == S.length c -> (True, Chunk c bs)
                   | otherwise                 -> (False, fromStrict c' `append` bs)

-- | Similar to 'P.dropWhile',
-- drops the longest (possibly empty) prefix of elements
-- satisfying the predicate and returns the remainder.
dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
dropWhile f = dropWhile'
  where dropWhile' Empty        = Empty
        dropWhile' (Chunk c cs) =
          case S.findIndexOrLength (not . f) c of
            n | n < S.length c -> Chunk (S.drop n c) cs
              | otherwise      -> dropWhile' cs

-- | Similar to 'P.dropWhileEnd',
-- drops the longest (possibly empty) suffix of elements
-- satisfying the predicate and returns the remainder.
--
-- @'dropWhileEnd' p@ is equivalent to @'reverse' . 'dropWhile' p . 'reverse'@.
--
-- >>> {-# LANGUAGE OverloadedLists #-)
-- >>> dropWhileEnd even [1,2,3,4,6]
-- [1,2,3]
--
-- @since 0.11.2.0
dropWhileEnd :: (Word8 -> Bool) -> ByteString -> ByteString
dropWhileEnd f = go []
  where go acc (Chunk c cs)
            | f (S.last c) = go (c : acc) cs
            | otherwise    = List.foldl (flip Chunk) (go [] cs) (c : acc)
        go acc Empty       = dropEndBytes acc
        dropEndBytes []         = Empty
        dropEndBytes (x : xs)   =
            case S.dropWhileEnd f x of
                 x' | S.null x' -> dropEndBytes xs
                    | otherwise -> List.foldl' (flip Chunk) Empty (x' : xs)

-- | Similar to 'P.break',
-- returns the longest (possibly empty) prefix of elements which __do not__
-- satisfy the predicate and the remainder of the string.
--
-- 'break' @p@ is equivalent to @'span' (not . p)@ and to @('takeWhile' (not . p) &&& 'dropWhile' (not . p))@.
--
break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
break f = break'
  where break' Empty        = (Empty, Empty)
        break' (Chunk c cs) =
          case S.findIndexOrLength f c of
            0                  -> (Empty, Chunk c cs)
            n | n < S.length c -> (Chunk (S.take n c) Empty
                                  ,Chunk (S.drop n c) cs)
              | otherwise      -> let (cs', cs'') = break' cs
                                   in (Chunk c cs', cs'')


-- | Returns the longest (possibly empty) suffix of elements which __do not__
-- satisfy the predicate and the remainder of the string.
--
-- 'breakEnd' @p@ is equivalent to @'spanEnd' (not . p)@ and to @('takeWhileEnd' (not . p) &&& 'dropWhileEnd' (not . p))@.
--
-- @since 0.11.2.0
breakEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
breakEnd  f = go []
  where go acc (Chunk c cs)
            | f (S.last c) = List.foldl (flip $ BF.first . Chunk) (go [] cs) (c : acc)
            | otherwise = go (c : acc) cs
        go acc Empty = dropEndBytes acc
        dropEndBytes [] = (Empty, Empty)
        dropEndBytes (x : xs) =
            case S.breakEnd f x of
                 (x', x'') | S.null x' -> let (y, y') = dropEndBytes xs
                                           in (y, y' `append` fromStrict x)
                           | otherwise ->
                                List.foldl' (flip $ BF.first . Chunk) (fromStrict x', fromStrict x'') xs


--
-- TODO
--
-- Add rules
--

{-
-- | 'breakByte' breaks its ByteString argument at the first occurence
-- of the specified byte. It is more efficient than 'break' as it is
-- implemented with @memchr(3)@. I.e.
--
-- > break (==99) "abcd" == breakByte 99 "abcd" -- fromEnum 'c' == 99
--
breakByte :: Word8 -> ByteString -> (ByteString, ByteString)
breakByte c (LPS ps) = case (breakByte' ps) of (a,b) -> (LPS a, LPS b)
  where breakByte' []     = ([], [])
        breakByte' (x:xs) =
          case P.elemIndex c x of
            Just 0  -> ([], x : xs)
            Just n  -> (P.take n x : [], P.drop n x : xs)
            Nothing -> let (xs', xs'') = breakByte' xs
                        in (x : xs', xs'')

-- | 'spanByte' breaks its ByteString argument at the first
-- occurence of a byte other than its argument. It is more efficient
-- than 'span (==)'
--
-- > span  (==99) "abcd" == spanByte 99 "abcd" -- fromEnum 'c' == 99
--
spanByte :: Word8 -> ByteString -> (ByteString, ByteString)
spanByte c (LPS ps) = case (spanByte' ps) of (a,b) -> (LPS a, LPS b)
  where spanByte' []     = ([], [])
        spanByte' (x:xs) =
          case P.spanByte c x of
            (x', x'') | P.null x'  -> ([], x : xs)
                      | P.null x'' -> let (xs', xs'') = spanByte' xs
                                       in (x : xs', xs'')
                      | otherwise  -> (x' : [], x'' : xs)
-}

-- | Similar to 'P.span',
-- returns the longest (possibly empty) prefix of elements
-- satisfying the predicate and the remainder of the string.
--
-- 'span' @p@ is equivalent to @'break' (not . p)@ and to @('takeWhile' p &&& 'dropWhile' p)@.
--
span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
span p = break (not . p)

-- | Returns the longest (possibly empty) suffix of elements
-- satisfying the predicate and the remainder of the string.
--
-- 'spanEnd' @p@ is equivalent to @'breakEnd' (not . p)@ and to @('takeWhileEnd' p &&& 'dropWhileEnd' p)@.
--
-- We have
--
-- > spanEnd (not . isSpace) "x y z" == ("x y ", "z")
--
-- and
--
-- > spanEnd (not . isSpace) ps
-- >    ==
-- > let (x, y) = span (not . isSpace) (reverse ps) in (reverse y, reverse x)
--
-- @since 0.11.2.0
spanEnd :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
spanEnd p = breakEnd (not . p)

-- | /O(n)/ Splits a 'ByteString' into components delimited by
-- separators, where the predicate returns True for a separator element.
-- The resulting components do not contain the separators.  Two adjacent
-- separators result in an empty component in the output.  eg.
--
-- > splitWith (==97) "aabbaca" == ["","","bb","c",""] -- fromEnum 'a' == 97
-- > splitWith undefined ""     == []                  -- and not [""]
--
splitWith :: (Word8 -> Bool) -> ByteString -> [ByteString]
splitWith _ Empty          = []
splitWith p (Chunk c0 cs0) = comb [] (S.splitWith p c0) cs0

  where comb :: [P.ByteString] -> [P.ByteString] -> ByteString -> [ByteString]
        comb acc [s] Empty        = [revChunks (s:acc)]
        comb acc [s] (Chunk c cs) = comb (s:acc) (S.splitWith p c) cs
        comb acc (s:ss) cs        = revChunks (s:acc) : comb [] ss cs
{-# INLINE splitWith #-}

-- | /O(n)/ Break a 'ByteString' into pieces separated by the byte
-- argument, consuming the delimiter. I.e.
--
-- > split 10  "a\nb\nd\ne" == ["a","b","d","e"]   -- fromEnum '\n' == 10
-- > split 97  "aXaXaXa"    == ["","X","X","X",""] -- fromEnum 'a' == 97
-- > split 120 "x"          == ["",""]             -- fromEnum 'x' == 120
-- > split undefined ""     == []                  -- and not [""]
--
-- and
--
-- > intercalate [c] . split c == id
-- > split == splitWith . (==)
--
-- As for all splitting functions in this library, this function does
-- not copy the substrings, it just constructs new 'ByteString's that
-- are slices of the original.
--
split :: Word8 -> ByteString -> [ByteString]
split _ Empty     = []
split w (Chunk c0 cs0) = comb [] (S.split w c0) cs0

  where comb :: [P.ByteString] -> [P.ByteString] -> ByteString -> [ByteString]
        comb acc [s] Empty        = [revChunks (s:acc)]
        comb acc [s] (Chunk c cs) = comb (s:acc) (S.split w c) cs
        comb acc (s:ss) cs        = revChunks (s:acc) : comb [] ss cs
{-# INLINE split #-}

-- | The 'group' function takes a ByteString and returns a list of
-- ByteStrings such that the concatenation of the result is equal to the
-- argument.  Moreover, each sublist in the result contains only equal
-- elements.  For example,
--
-- > group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]
--
-- It is a special case of 'groupBy', which allows the programmer to
-- supply their own equality test.
group :: ByteString -> [ByteString]
group = go
  where
    go Empty        = []
    go (Chunk c cs)
      | S.length c == 1  = to [c] (S.unsafeHead c) cs
      | otherwise        = to [S.unsafeTake 1 c] (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)

    to acc !_ Empty        = [revNonEmptyChunks acc]
    to acc !w (Chunk c cs) =
      case S.findIndexOrLength (/= w) c of
        0                    -> revNonEmptyChunks acc
                              : go (Chunk c cs)
        n | n == S.length c  -> to (S.unsafeTake n c : acc) w cs
          | otherwise        -> revNonEmptyChunks (S.unsafeTake n c : acc)
                              : go (Chunk (S.unsafeDrop n c) cs)

-- | The 'groupBy' function is the non-overloaded version of 'group'.
--
groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
groupBy k = go
  where
    go Empty        = []
    go (Chunk c cs)
      | S.length c == 1  = to [c] (S.unsafeHead c) cs
      | otherwise        = to [S.unsafeTake 1 c] (S.unsafeHead c) (Chunk (S.unsafeTail c) cs)

    to acc !_ Empty        = [revNonEmptyChunks acc]
    to acc !w (Chunk c cs) =
      case S.findIndexOrLength (not . k w) c of
        0                    -> revNonEmptyChunks acc
                              : go (Chunk c cs)
        n | n == S.length c  -> to (S.unsafeTake n c : acc) w cs
          | otherwise        -> revNonEmptyChunks (S.unsafeTake n c : acc)
                              : go (Chunk (S.unsafeDrop n c) cs)

-- | /O(n)/ The 'intercalate' function takes a 'ByteString' and a list of
-- 'ByteString's and concatenates the list after interspersing the first
-- argument between each element of the list.
intercalate :: ByteString -> [ByteString] -> ByteString
intercalate s = concat . List.intersperse s

-- ---------------------------------------------------------------------
-- Indexing ByteStrings

-- | /O(c)/ 'ByteString' index (subscript) operator, starting from 0.
index :: HasCallStack => ByteString -> Int64 -> Word8
index _  i | i < 0  = moduleError "index" ("negative index: " ++ show i)
index cs0 i         = index' cs0 i
  where index' Empty     n = moduleError "index" ("index too large: " ++ show n)
        index' (Chunk c cs) n
          | n >= fromIntegral (S.length c) =
              index' cs (n - fromIntegral (S.length c))
          | otherwise       = S.unsafeIndex c (fromIntegral n)

-- | /O(c)/ 'ByteString' index, starting from 0, that returns 'Just' if:
--
-- > 0 <= n < length bs
--
-- @since 0.11.0.0
indexMaybe :: ByteString -> Int64 -> Maybe Word8
indexMaybe _ i | i < 0 = Nothing
indexMaybe cs0 i       = index' cs0 i
  where index' Empty _ = Nothing
        index' (Chunk c cs) n
          | n >= fromIntegral (S.length c) =
              index' cs (n - fromIntegral (S.length c))
          | otherwise       = Just $! S.unsafeIndex c (fromIntegral n)

-- | /O(1)/ 'ByteString' index, starting from 0, that returns 'Just' if:
--
-- > 0 <= n < length bs
--
-- @since 0.11.0.0
(!?) :: ByteString -> Int64 -> Maybe Word8
(!?) = indexMaybe
{-# INLINE (!?) #-}

-- | /O(n)/ The 'elemIndex' function returns the index of the first
-- element in the given 'ByteString' which is equal to the query
-- element, or 'Nothing' if there is no such element.
-- This implementation uses memchr(3).
elemIndex :: Word8 -> ByteString -> Maybe Int64
elemIndex w = elemIndex' 0
  where elemIndex' _ Empty        = Nothing
        elemIndex' n (Chunk c cs) =
          case S.elemIndex w c of
            Nothing -> elemIndex' (n + fromIntegral (S.length c)) cs
            Just i  -> Just (n + fromIntegral i)

-- | /O(n)/ The 'elemIndexEnd' function returns the last index of the
-- element in the given 'ByteString' which is equal to the query
-- element, or 'Nothing' if there is no such element. The following
-- holds:
--
-- > elemIndexEnd c xs = case elemIndex c (reverse xs) of
-- >   Nothing -> Nothing
-- >   Just i  -> Just (length xs - 1 - i)
--
-- @since 0.10.6.0
elemIndexEnd :: Word8 -> ByteString -> Maybe Int64
elemIndexEnd = findIndexEnd . (==)
{-# INLINE elemIndexEnd #-}

-- | /O(n)/ The 'elemIndices' function extends 'elemIndex', by returning
-- the indices of all elements equal to the query element, in ascending order.
-- This implementation uses memchr(3).
elemIndices :: Word8 -> ByteString -> [Int64]
elemIndices w = elemIndices' 0
  where elemIndices' _ Empty        = []
        elemIndices' n (Chunk c cs) = List.map ((+n).fromIntegral) (S.elemIndices w c)
                             ++ elemIndices' (n + fromIntegral (S.length c)) cs

-- | count returns the number of times its argument appears in the ByteString
--
-- > count = length . elemIndices
--
-- But more efficiently than using length on the intermediate list.
count :: Word8 -> ByteString -> Int64
count w = foldlChunks (\n c -> n + fromIntegral (S.count w c)) 0

-- | The 'findIndex' function takes a predicate and a 'ByteString' and
-- returns the index of the first element in the ByteString
-- satisfying the predicate.
findIndex :: (Word8 -> Bool) -> ByteString -> Maybe Int64
findIndex k = findIndex' 0
  where findIndex' _ Empty        = Nothing
        findIndex' n (Chunk c cs) =
          case S.findIndex k c of
            Nothing -> findIndex' (n + fromIntegral (S.length c)) cs
            Just i  -> Just (n + fromIntegral i)
{-# INLINE findIndex #-}

-- | The 'findIndexEnd' function takes a predicate and a 'ByteString' and
-- returns the index of the last element in the ByteString
-- satisfying the predicate.
--
-- @since 0.10.12.0
findIndexEnd :: (Word8 -> Bool) -> ByteString -> Maybe Int64
findIndexEnd k = findIndexEnd' 0
  where
    findIndexEnd' _ Empty = Nothing
    findIndexEnd' n (Chunk c cs) =
      let !n' = n + S.length c
          !i  = fromIntegral . (n +) <$> S.findIndexEnd k c
      in findIndexEnd' n' cs `mplus` i
{-# INLINE findIndexEnd #-}

-- | /O(n)/ The 'find' function takes a predicate and a ByteString,
-- and returns the first element in matching the predicate, or 'Nothing'
-- if there is no such element.
--
-- > find f p = case findIndex f p of Just n -> Just (p ! n) ; _ -> Nothing
--
find :: (Word8 -> Bool) -> ByteString -> Maybe Word8
find f = find'
  where find' Empty        = Nothing
        find' (Chunk c cs) = case S.find f c of
            Nothing -> find' cs
            Just w  -> Just w
{-# INLINE find #-}

-- | The 'findIndices' function extends 'findIndex', by returning the
-- indices of all elements satisfying the predicate, in ascending order.
findIndices :: (Word8 -> Bool) -> ByteString -> [Int64]
findIndices k = findIndices' 0
  where findIndices' _ Empty        = []
        findIndices' n (Chunk c cs) = List.map ((+n).fromIntegral) (S.findIndices k c)
                             ++ findIndices' (n + fromIntegral (S.length c)) cs
{-# INLINE findIndices #-}

-- ---------------------------------------------------------------------
-- Searching ByteStrings

-- | /O(n)/ 'elem' is the 'ByteString' membership predicate.
elem :: Word8 -> ByteString -> Bool
elem w cs = case elemIndex w cs of Nothing -> False ; _ -> True

-- | /O(n)/ 'notElem' is the inverse of 'elem'
notElem :: Word8 -> ByteString -> Bool
notElem w cs = not (w `elem` cs)

-- | /O(n)/ 'filter', applied to a predicate and a ByteString,
-- returns a ByteString containing those characters that satisfy the
-- predicate.
filter :: (Word8 -> Bool) -> ByteString -> ByteString
filter p = go
    where
        go Empty        = Empty
        go (Chunk x xs) = chunk (S.filter p x) (go xs)
{-# INLINE filter #-}

{-
-- | /O(n)/ and /O(n\/c) space/ A first order equivalent of /filter .
-- (==)/, for the common case of filtering a single byte. It is more
-- efficient to use /filterByte/ in this case.
--
-- > filterByte == filter . (==)
--
-- filterByte is around 10x faster, and uses much less space, than its
-- filter equivalent
filterByte :: Word8 -> ByteString -> ByteString
filterByte w ps = replicate (count w ps) w
{-# INLINE filterByte #-}

{-# RULES
"ByteString specialise filter (== x)" forall x.
  filter ((==) x) = filterByte x

"ByteString specialise filter (== x)" forall x.
 filter (== x) = filterByte x
  #-}
-}

{-
-- | /O(n)/ A first order equivalent of /filter . (\/=)/, for the common
-- case of filtering a single byte out of a list. It is more efficient
-- to use /filterNotByte/ in this case.
--
-- > filterNotByte == filter . (/=)
--
-- filterNotByte is around 2x faster than its filter equivalent.
filterNotByte :: Word8 -> ByteString -> ByteString
filterNotByte w (LPS xs) = LPS (filterMap (P.filterNotByte w) xs)
-}

-- | /O(n)/ The 'partition' function takes a predicate a ByteString and returns
-- the pair of ByteStrings with elements which do and do not satisfy the
-- predicate, respectively; i.e.,
--
-- > partition p bs == (filter p xs, filter (not . p) xs)
--
partition :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
partition _ Empty = (Empty, Empty)
partition p (Chunk x xs) = (chunk t ts, chunk f fs)
  where
    (t,   f) = S.partition p x
    (ts, fs) = partition   p xs

-- ---------------------------------------------------------------------
-- Searching for substrings

-- | /O(n)/ The 'isPrefixOf' function takes two ByteStrings and returns 'True'
-- iff the first is a prefix of the second.
isPrefixOf :: ByteString -> ByteString -> Bool
isPrefixOf Empty _  = True
isPrefixOf _ Empty  = False
isPrefixOf (Chunk x xs) (Chunk y ys)
    | S.length x == S.length y = x == y  && isPrefixOf xs ys
    | S.length x <  S.length y = x == yh && isPrefixOf xs (Chunk yt ys)
    | otherwise                = xh == y && isPrefixOf (Chunk xt xs) ys
  where (xh,xt) = S.splitAt (S.length y) x
        (yh,yt) = S.splitAt (S.length x) y

-- | /O(n)/ The 'stripPrefix' function takes two ByteStrings and returns 'Just'
-- the remainder of the second iff the first is its prefix, and otherwise
-- 'Nothing'.
--
-- @since 0.10.8.0
stripPrefix :: ByteString -> ByteString -> Maybe ByteString
stripPrefix Empty bs  = Just bs
stripPrefix _ Empty  = Nothing
stripPrefix (Chunk x xs) (Chunk y ys)
    | S.length x == S.length y = if x == y then stripPrefix xs ys else Nothing
    | S.length x <  S.length y = do yt <- S.stripPrefix x y
                                    stripPrefix xs (Chunk yt ys)
    | otherwise                = do xt <- S.stripPrefix y x
                                    stripPrefix (Chunk xt xs) ys

-- | /O(n)/ The 'isSuffixOf' function takes two ByteStrings and returns 'True'
-- iff the first is a suffix of the second.
--
-- The following holds:
--
-- > isSuffixOf x y == reverse x `isPrefixOf` reverse y
--
isSuffixOf :: ByteString -> ByteString -> Bool
isSuffixOf x y = reverse x `isPrefixOf` reverse y
--TODO: a better implementation

-- | /O(n)/ The 'stripSuffix' function takes two ByteStrings and returns 'Just'
-- the remainder of the second iff the first is its suffix, and otherwise
-- 'Nothing'.
stripSuffix :: ByteString -> ByteString -> Maybe ByteString
stripSuffix x y = reverse <$> stripPrefix (reverse x) (reverse y)
--TODO: a better implementation

-- ---------------------------------------------------------------------
-- Zipping

-- | /O(n)/ 'zip' takes two ByteStrings and returns a list of
-- corresponding pairs of bytes. If one input ByteString is short,
-- excess elements of the longer ByteString are discarded. This is
-- equivalent to a pair of 'unpack' operations.
zip :: ByteString -> ByteString -> [(Word8,Word8)]
zip = zipWith (,)

-- | 'zipWith' generalises 'zip' by zipping with the function given as
-- the first argument, instead of a tupling function.  For example,
-- @'zipWith' (+)@ is applied to two ByteStrings to produce the list of
-- corresponding sums.
zipWith :: (Word8 -> Word8 -> a) -> ByteString -> ByteString -> [a]
zipWith _ Empty     _  = []
zipWith _ _      Empty = []
zipWith f (Chunk a as) (Chunk b bs) = go a as b bs
  where
    go x xs y ys = f (S.unsafeHead x) (S.unsafeHead y)
                 : to (S.unsafeTail x) xs (S.unsafeTail y) ys

    to x Empty         _ _             | S.null x       = []
    to _ _             y Empty         | S.null y       = []
    to x xs            y ys            | not (S.null x)
                                      && not (S.null y) = go x  xs y  ys
    to x xs            _ (Chunk y' ys) | not (S.null x) = go x  xs y' ys
    to _ (Chunk x' xs) y ys            | not (S.null y) = go x' xs y  ys
    to _ (Chunk x' xs) _ (Chunk y' ys)                  = go x' xs y' ys

-- | A specialised version of `zipWith` for the common case of a
-- simultaneous map over two ByteStrings, to build a 3rd.
--
-- @since 0.11.1.0
packZipWith :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString -> ByteString
packZipWith _ Empty _ = Empty
packZipWith _ _ Empty = Empty
packZipWith f (Chunk a@(S.BS _ al) as) (Chunk b@(S.BS _ bl) bs) = Chunk (S.packZipWith f a b) $
    case compare al bl of
        LT -> packZipWith f as $ Chunk (S.drop al b) bs
        EQ -> packZipWith f as bs
        GT -> packZipWith f (Chunk (S.drop bl a) as) bs
{-# INLINE packZipWith #-}

-- | /O(n)/ 'unzip' transforms a list of pairs of bytes into a pair of
-- ByteStrings. Note that this performs two 'pack' operations.
unzip :: [(Word8,Word8)] -> (ByteString,ByteString)
unzip ls = (pack (List.map fst ls), pack (List.map snd ls))
{-# INLINE unzip #-}

-- ---------------------------------------------------------------------
-- Special lists

-- | /O(n)/ Return all initial segments of the given 'ByteString', shortest first.
inits :: ByteString -> [ByteString]
inits = (Empty :) . inits'
  where inits' Empty        = []
        inits' (Chunk c cs) = List.map (`Chunk` Empty) (List.tail (S.inits c))
                           ++ List.map (Chunk c) (inits' cs)

-- | /O(n)/ Return all final segments of the given 'ByteString', longest first.
tails :: ByteString -> [ByteString]
tails Empty         = [Empty]
tails cs@(Chunk c cs')
  | S.length c == 1 = cs : tails cs'
  | otherwise       = cs : tails (Chunk (S.unsafeTail c) cs')

-- ---------------------------------------------------------------------
-- Low level constructors

-- | /O(n)/ Make a copy of the 'ByteString' with its own storage.
--   This is mainly useful to allow the rest of the data pointed
--   to by the 'ByteString' to be garbage collected, for example
--   if a large string has been read in, and only a small part of it
--   is needed in the rest of the program.
copy :: ByteString -> ByteString
copy = foldrChunks (Chunk . S.copy) Empty
--TODO, we could coalese small blocks here
--FIXME: probably not strict enough, if we're doing this to avoid retaining
-- the parent blocks then we'd better copy strictly.

-- ---------------------------------------------------------------------

-- TODO defrag func that concatenates block together that are below a threshold
-- defrag :: ByteString -> ByteString

-- ---------------------------------------------------------------------
-- Lazy ByteString IO
--
-- Rule for when to close: is it expected to read the whole file?
-- If so, close when done.
--

-- | Read entire handle contents /lazily/ into a 'ByteString'. Chunks
-- are read on demand, in at most @k@-sized chunks. It does not block
-- waiting for a whole @k@-sized chunk, so if less than @k@ bytes are
-- available then they will be returned immediately as a smaller chunk.
--
-- The handle is closed on EOF.
--
hGetContentsN :: Int -> Handle -> IO ByteString
hGetContentsN k h = lazyRead -- TODO close on exceptions
  where
    lazyRead = unsafeInterleaveIO loop

    loop = do
        c <- S.hGetSome h k -- only blocks if there is no data available
        if S.null c
          then hClose h >> return Empty
          else Chunk c <$> lazyRead

-- | Read @n@ bytes into a 'ByteString', directly from the
-- specified 'Handle', in chunks of size @k@.
--
hGetN :: Int -> Handle -> Int -> IO ByteString
hGetN k h n | n > 0 = readChunks n
  where
    readChunks !i = do
        c <- S.hGet h (min k i)
        case S.length c of
            0 -> return Empty
            m -> do cs <- readChunks (i - m)
                    return (Chunk c cs)

hGetN _ _ 0 = return Empty
hGetN _ h n = illegalBufferSize h "hGet" n

-- | hGetNonBlockingN is similar to 'hGetContentsN', except that it will never block
-- waiting for data to become available, instead it returns only whatever data
-- is available. Chunks are read on demand, in @k@-sized chunks.
--
hGetNonBlockingN :: Int -> Handle -> Int -> IO ByteString
hGetNonBlockingN k h n | n > 0= readChunks n
  where
    readChunks !i = do
        c <- S.hGetNonBlocking h (min k i)
        case S.length c of
            0 -> return Empty
            m -> do cs <- readChunks (i - m)
                    return (Chunk c cs)

hGetNonBlockingN _ _ 0 = return Empty
hGetNonBlockingN _ h n = illegalBufferSize h "hGetNonBlocking" n

illegalBufferSize :: Handle -> String -> Int -> IO a
illegalBufferSize handle fn sz =
    ioError (mkIOError illegalOperationErrorType msg (Just handle) Nothing)
    --TODO: System.IO uses InvalidArgument here, but it's not exported :-(
    where
      msg = fn ++ ": illegal ByteString size " ++ showsPrec 9 sz []

-- | Read entire handle contents /lazily/ into a 'ByteString'. Chunks
-- are read on demand, using the default chunk size.
--
-- File handles are closed on EOF if all the file is read, or through
-- garbage collection otherwise.
--
hGetContents :: Handle -> IO ByteString
hGetContents = hGetContentsN defaultChunkSize

-- | Read @n@ bytes into a 'ByteString', directly from the specified 'Handle'.
--
hGet :: Handle -> Int -> IO ByteString
hGet = hGetN defaultChunkSize

-- | hGetNonBlocking is similar to 'hGet', except that it will never block
-- waiting for data to become available, instead it returns only whatever data
-- is available.  If there is no data available to be read, 'hGetNonBlocking'
-- returns 'empty'.
--
-- Note: on Windows and with Haskell implementation other than GHC, this
-- function does not work correctly; it behaves identically to 'hGet'.
--
hGetNonBlocking :: Handle -> Int -> IO ByteString
hGetNonBlocking = hGetNonBlockingN defaultChunkSize

-- | Read an entire file /lazily/ into a 'ByteString'.
--
-- The 'Handle' will be held open until EOF is encountered.
--
-- Note that this function's implementation relies on 'hGetContents'.
-- The reader is advised to read its documentation.
--
readFile :: FilePath -> IO ByteString
readFile f = openBinaryFile f ReadMode >>= hGetContents

modifyFile :: IOMode -> FilePath -> ByteString -> IO ()
modifyFile mode f txt = withBinaryFile f mode (`hPut` txt)

-- | Write a 'ByteString' to a file.
--
writeFile :: FilePath -> ByteString -> IO ()
writeFile = modifyFile WriteMode

-- | Append a 'ByteString' to a file.
--
appendFile :: FilePath -> ByteString -> IO ()
appendFile = modifyFile AppendMode

-- | getContents. Equivalent to hGetContents stdin. Will read /lazily/
--
getContents :: IO ByteString
getContents = hGetContents stdin

-- | Outputs a 'ByteString' to the specified 'Handle'. The chunks will be
-- written one at a time. Other threads might write to the 'Handle' between the
-- writes, and hence 'hPut' alone might not be suitable for concurrent writes.
--
hPut :: Handle -> ByteString -> IO ()
hPut h = foldrChunks (\c rest -> S.hPut h c >> rest) (return ())

-- | Similar to 'hPut' except that it will never block. Instead it returns
-- any tail that did not get written. This tail may be 'empty' in the case that
-- the whole string was written, or the whole original string if nothing was
-- written. Partial writes are also possible.
--
-- Note: on Windows and with Haskell implementation other than GHC, this
-- function does not work correctly; it behaves identically to 'hPut'.
--
hPutNonBlocking :: Handle -> ByteString -> IO ByteString
hPutNonBlocking _ Empty           = return Empty
hPutNonBlocking h bs@(Chunk c cs) = do
  c' <- S.hPutNonBlocking h c
  case S.length c' of
    l' | l' == S.length c -> hPutNonBlocking h cs
    0                     -> return bs
    _                     -> return (Chunk c' cs)

-- | A synonym for @hPut@, for compatibility
--
hPutStr :: Handle -> ByteString -> IO ()
hPutStr = hPut

-- | Write a ByteString to stdout
putStr :: ByteString -> IO ()
putStr = hPut stdout

-- | The interact function takes a function of type @ByteString -> ByteString@
-- as its argument. The entire input from the standard input device is passed
-- to this function as its argument, and the resulting string is output on the
-- standard output device.
--
interact :: (ByteString -> ByteString) -> IO ()
interact transformer = putStr . transformer =<< getContents

-- ---------------------------------------------------------------------
-- Internal utilities

-- Common up near identical calls to `error' to reduce the number
-- constant strings created when compiled:
errorEmptyList :: HasCallStack => String -> a
errorEmptyList fun = moduleError fun "empty ByteString"
{-# NOINLINE errorEmptyList #-}

moduleError :: HasCallStack => String -> String -> a
moduleError fun msg = error ("Data.ByteString.Lazy." ++ fun ++ ':':' ':msg)
{-# NOINLINE moduleError #-}


-- reverse a list of non-empty chunks into a lazy ByteString
revNonEmptyChunks :: [P.ByteString] -> ByteString
revNonEmptyChunks = List.foldl' (flip Chunk) Empty

-- reverse a list of possibly-empty chunks into a lazy ByteString
revChunks :: [P.ByteString] -> ByteString
revChunks = List.foldl' (flip chunk) Empty

-- $IOChunk
--
-- ⚠ Using lazy I\/O functions like 'readFile' or 'hGetContents'
-- means that the order of operations such as closing the file handle
-- is left at the discretion of the RTS.
-- Hence, the developer can face some issues when:
--
-- * The program reads a file and writes the same file. This means that the file
--   may be locked because the handler has not been released when 'writeFile' is executed.
-- * The program reads thousands of files, but due to lazy evaluation, the OS's file descriptor
--   limit is reached before the handlers can be released.
--
-- === Why?
--
-- Consider the following program:
--
-- > import qualified Data.ByteString.Lazy as BL
-- > main = do
-- >   _ <- BL.readFile "foo.txt"
-- >   BL.writeFile "foo.txt" mempty
--
-- Generally, in the 'IO' monad side effects happen
-- sequentially and in full. Therefore, one might reasonably expect that
-- reading the whole file via 'readFile' executes all three actions
-- (open the file handle, read its content, close the file handle) before
-- control moves to the following 'writeFile' action. This expectation holds
-- for the strict "Data.ByteString" API. However, the above lazy 'ByteString' variant
-- of the program fails with @openBinaryFile: resource busy (file is locked)@.
--
-- The reason for this is that "Data.ByteString.Lazy" is specifically designed
-- to handle large or unbounded streams of data incrementally, without requiring all the data
-- to be resident in memory at the same time. Incremental processing would not be possible
-- if 'readFile' were to follow the usual rules of 'IO': evaluating all side effects
-- would require reading the file in full and closing its handle before returning from 'readFile'. This is why
-- 'readFile' (and 'hGetContents' in general) is implemented
-- via 'unsafeInterleaveIO', which allows 'IO' side effects to be delayed and
-- interleaved with subsequent processing of the return value.
-- That's exactly what happens
-- in the example above: 'readFile' opens a file handle, but since the content
-- is not fully consumed, the file handle remains open, allowing the content to
-- read __on demand__ (never in this case, since the return value is ignored).
-- So when 'writeFile' is executed next, @foo.txt@ is still open for reading and
-- the RTS takes care to avoid simultaneously opening it for writing, instead
-- returning the error shown above.
--
-- === How to enforce the order of effects?
--
-- If the content is small enough to fit in memory,
-- consider using strict 'Data.ByteString.readFile',
-- potentially applying 'fromStrict' afterwards. E. g.,
--
-- > import qualified Data.ByteString as BS
-- > import qualified Data.ByteString.Lazy as BL
-- > main = do
-- >   _ <- BS.readFile "foo.txt"
-- >   BL.writeFile "foo.txt" mempty
--
-- If you are dealing with large or unbounded data streams,
-- consider reaching out for a specialised package, such as
-- <http://hackage.haskell.org/package/conduit conduit>,
-- <http://hackage.haskell.org/package/machines-bytestring machines-bytestring>,
-- <http://hackage.haskell.org/package/pipes-bytestring pipes-bytestring>,
-- <http://hackage.haskell.org/package/streaming-bytestring streaming-bytestring>,
-- <http://hackage.haskell.org/package/streamly-bytestring streamly-bytestring>,
-- etc.