{-# LANGUAGE CPP, BangPatterns #-}

#if __GLASGOW_HASKELL__ >= 704
{-# LANGUAGE Trustworthy #-}
#endif

{-# OPTIONS_GHC -fno-warn-incomplete-patterns
                -fno-warn-orphans
  #-}

-- |
-- Module      : Data.Vector.Storable.ByteString.Lazy
-- Copyright   : (c) Don Stewart 2006
--               (c) Duncan Coutts 2006
--               (c) Bas van Dijk 2011
-- License     : BSD-style
--
-- Maintainer  : Bas van Dijk <v.dijk.bas@gmail.com>
-- Stability   : experimental
-- 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. Byte vectors are encoded as lazy lists of strict 'Word8'
-- arrays of bytes. They provide a means to manipulate large byte vectors
-- without requiring the entire vector be resident in memory.
--
-- 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. And for other
-- operations lazy ByteStrings are usually within a few percent of
-- strict ones, but with better heap usage. For data larger than the
-- available memory, or if you have tight memory constraints, this
-- module will be the only option. The default chunk size is 64k, which
-- should be good in most circumstances. For people with large L2
-- caches, you may want to increase this to fit your cache.
--
-- This module is intended to be imported @qualified@, to avoid name
-- clashes with "Prelude" functions.  eg.
--
-- > import qualified Data.Vector.Storable.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.
-- Polished and extended by Don Stewart.
-- Lazy variant by Duncan Coutts and Don Stewart.
--

module Data.Vector.Storable.ByteString.Lazy (

        -- * The @ByteString@ type
        ByteString,             -- instances: Eq, Ord, Show, Read, Data, Typeable

        -- * Introducing and eliminating 'ByteString's
        empty,                  -- :: ByteString
        singleton,              -- :: Word8   -> ByteString
        pack,                   -- :: [Word8] -> ByteString
        unpack,                 -- :: ByteString -> [Word8]
        fromChunks,             -- :: [Strict.ByteString] -> ByteString
        toChunks,               -- :: ByteString -> [Strict.ByteString]

        -- * Basic interface
        cons,                   -- :: Word8 -> ByteString -> ByteString
        cons',                  -- :: Word8 -> ByteString -> ByteString
        snoc,                   -- :: ByteString -> Word8 -> ByteString
        append,                 -- :: ByteString -> ByteString -> ByteString
        head,                   -- :: ByteString -> Word8
        uncons,                 -- :: ByteString -> Maybe (Word8, ByteString)
        last,                   -- :: ByteString -> Word8
        tail,                   -- :: ByteString -> ByteString
        init,                   -- :: ByteString -> ByteString
        null,                   -- :: ByteString -> Bool
        length,                 -- :: ByteString -> Int64

        -- * Transforming ByteStrings
        map,                    -- :: (Word8 -> Word8) -> ByteString -> ByteString
        reverse,                -- :: ByteString -> ByteString
        intersperse,            -- :: Word8 -> ByteString -> ByteString
        intercalate,            -- :: ByteString -> [ByteString] -> ByteString
        transpose,              -- :: [ByteString] -> [ByteString]

        -- * Reducing 'ByteString's (folds)
        foldl,                  -- :: (a -> Word8 -> a) -> a -> ByteString -> a
        foldl',                 -- :: (a -> Word8 -> a) -> a -> ByteString -> a
        foldl1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
        foldl1',                -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8
        foldr,                  -- :: (Word8 -> a -> a) -> a -> ByteString -> a
        foldr1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> Word8

        -- ** Special folds
        concat,                 -- :: [ByteString] -> ByteString
        concatMap,              -- :: (Word8 -> ByteString) -> ByteString -> ByteString
        any,                    -- :: (Word8 -> Bool) -> ByteString -> Bool
        all,                    -- :: (Word8 -> Bool) -> ByteString -> Bool
        maximum,                -- :: ByteString -> Word8
        minimum,                -- :: ByteString -> Word8

        -- * Building ByteStrings
        -- ** Scans
        scanl,                  -- :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
--        scanl1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString
--        scanr,                  -- :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
--        scanr1,                 -- :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString

        -- ** Accumulating maps
        mapAccumL,              -- :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)
        mapAccumR,              -- :: (acc -> Word8 -> (acc, Word8)) -> acc -> ByteString -> (acc, ByteString)

        -- ** Infinite ByteStrings
        repeat,                 -- :: Word8 -> ByteString
        replicate,              -- :: Int64 -> Word8 -> ByteString
        cycle,                  -- :: ByteString -> ByteString
        iterate,                -- :: (Word8 -> Word8) -> Word8 -> ByteString

        -- ** Unfolding ByteStrings
        unfoldr,                -- :: (a -> Maybe (Word8, a)) -> a -> ByteString

        -- * Substrings

        -- ** Breaking strings
        take,                   -- :: Int64 -> ByteString -> ByteString
        drop,                   -- :: Int64 -> ByteString -> ByteString
        splitAt,                -- :: Int64 -> ByteString -> (ByteString, ByteString)
        takeWhile,              -- :: (Word8 -> Bool) -> ByteString -> ByteString
        dropWhile,              -- :: (Word8 -> Bool) -> ByteString -> ByteString
        span,                   -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
        break,                  -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
        group,                  -- :: ByteString -> [ByteString]
        groupBy,                -- :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
        inits,                  -- :: ByteString -> [ByteString]
        tails,                  -- :: ByteString -> [ByteString]

        -- ** Breaking into many substrings
        split,                  -- :: Word8 -> ByteString -> [ByteString]
        splitWith,              -- :: (Word8 -> Bool) -> ByteString -> [ByteString]

        -- * Predicates
        isPrefixOf,             -- :: ByteString -> ByteString -> Bool
        isSuffixOf,             -- :: ByteString -> ByteString -> Bool
--        isInfixOf,              -- :: ByteString -> ByteString -> Bool

        -- ** Search for arbitrary substrings
--        isSubstringOf,          -- :: ByteString -> ByteString -> Bool
--        findSubstring,          -- :: ByteString -> ByteString -> Maybe Int
--        findSubstrings,         -- :: ByteString -> ByteString -> [Int]

        -- * Searching ByteStrings

        -- ** Searching by equality
        elem,                   -- :: Word8 -> ByteString -> Bool
        notElem,                -- :: Word8 -> ByteString -> Bool

        -- ** Searching with a predicate
        find,                   -- :: (Word8 -> Bool) -> ByteString -> Maybe Word8
        filter,                 -- :: (Word8 -> Bool) -> ByteString -> ByteString
        partition,              -- :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)

        -- * Indexing ByteStrings
        index,                  -- :: ByteString -> Int64 -> Word8
        elemIndex,              -- :: Word8 -> ByteString -> Maybe Int64
        elemIndices,            -- :: Word8 -> ByteString -> [Int64]
        findIndex,              -- :: (Word8 -> Bool) -> ByteString -> Maybe Int64
        findIndices,            -- :: (Word8 -> Bool) -> ByteString -> [Int64]
        count,                  -- :: Word8 -> ByteString -> Int64

        -- * Zipping and unzipping ByteStrings
        zip,                    -- :: ByteString -> ByteString -> [(Word8,Word8)]
        zipWith,                -- :: (Word8 -> Word8 -> c) -> ByteString -> ByteString -> [c]
        unzip,                  -- :: [(Word8,Word8)] -> (ByteString,ByteString)

        -- * Ordered ByteStrings
--        sort,                   -- :: ByteString -> ByteString

        -- * Low level conversions
        -- ** Copying ByteStrings
        copy,                   -- :: ByteString -> ByteString
--        defrag,                -- :: ByteString -> ByteString

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

        -- ** Standard input and output
        getContents,            -- :: IO ByteString
        putStr,                 -- :: ByteString -> IO ()
        putStrLn,               -- :: ByteString -> IO ()
        interact,               -- :: (ByteString -> ByteString) -> IO ()

        -- ** Files
        readFile,               -- :: FilePath -> IO ByteString
        writeFile,              -- :: FilePath -> ByteString -> IO ()
        appendFile,             -- :: FilePath -> ByteString -> IO ()

        -- ** I\/O with Handles
        hGetContents,           -- :: Handle -> IO ByteString
        hGet,                   -- :: Handle -> Int -> IO ByteString
        hGetNonBlocking,        -- :: Handle -> Int -> IO ByteString
        hPut,                   -- :: Handle -> ByteString -> IO ()
        hPutNonBlocking,        -- :: Handle -> ByteString -> IO ByteString
        hPutStr,                -- :: Handle -> ByteString -> IO ()

  ) 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 L  -- L for list/lazy
import qualified Data.Vector.Storable.ByteString        as P  (ByteString) -- type name only
import qualified Data.Vector.Storable.ByteString        as S  -- S for strict (hmm...)
import qualified Data.Vector.Storable.ByteString.Internal as S
import qualified Data.Vector.Storable.ByteString.Unsafe as S
import Data.Vector.Storable.ByteString.Lazy.Internal

import Data.Monoid              (Monoid(..))

import Data.Word                (Word8)
import Data.Int                 (Int64)
import System.IO                (Handle,stdin,stdout,openBinaryFile,IOMode(..)
                                ,hClose)
import System.IO.Error          (mkIOError, illegalOperationErrorType)
import System.IO.Unsafe
import Control.Exception        (bracket)

import Foreign.ForeignPtr       (withForeignPtr)
import Foreign.Ptr
import Foreign.Storable

-- from vector:
import qualified Data.Vector.Storable as VS
    ( unsafeToForeignPtr0, unsafeToForeignPtr0 )


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

instance Eq  ByteString
    where (==)    = eq

instance Ord ByteString
    where compare = cmp

instance Monoid ByteString where
    mempty  = empty
    mappend = append
    mconcat = concat

eq :: ByteString -> ByteString -> Bool
eq Empty Empty = True
eq Empty _     = False
eq _     Empty = False
eq (Chunk a as) (Chunk b bs) =
  case compare (S.length a) (S.length b) of
    LT -> a == (S.take (S.length a) b) && eq as (Chunk (S.drop (S.length a) b) bs)
    EQ -> a == b                       && eq as bs
    GT -> (S.take (S.length b) a) == b && eq (Chunk (S.drop (S.length b) a) as) bs

cmp :: ByteString -> ByteString -> Ordering
cmp Empty Empty = EQ
cmp Empty _     = LT
cmp _     Empty = GT
cmp (Chunk a as) (Chunk b bs) =
  case compare (S.length a) (S.length b) of
    LT -> case compare a (S.take (S.length a) b) of
            EQ     -> cmp as (Chunk (S.drop (S.length a) b) bs)
            result -> result
    EQ -> case compare a b of
            EQ     -> cmp as bs
            result -> result
    GT -> case compare (S.take (S.length b) a) b of
            EQ     -> cmp (Chunk (S.drop (S.length b) a) as) bs
            result -> result

-- -----------------------------------------------------------------------------
-- 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 ws = L.foldr (Chunk . S.pack) Empty (chunks defaultChunkSize ws)
  where
    chunks :: Int -> [a] -> [[a]]
    chunks _    [] = []
    chunks size xs = case L.splitAt size xs of
                      (xs', xs'') -> xs' : chunks size xs''

-- | /O(n)/ Converts a 'ByteString' to a '[Word8]'.
unpack :: ByteString -> [Word8]
unpack cs = L.concatMap S.unpack (toChunks cs)
--TODO: we can do better here by integrating the concat with the unpack

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

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

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

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

-- | /O(1)/ 'cons' is analogous to '(:)' for lists.
--
cons :: Word8 -> ByteString -> ByteString
cons c cs = Chunk (S.singleton c) cs
{-# 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 :: 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 :: 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 :: ByteString -> Word8
last Empty          = errorEmptyList "last"
last (Chunk c0 cs0) = go c0 cs0
  where go c Empty        = S.last 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 :: 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.init c) Empty
        go c (Chunk c' cs)           = Chunk c (go c' cs)

-- | /O(n\/c)/ Append two ByteStrings
append :: ByteString -> ByteString -> ByteString
append xs ys = foldrChunks Chunk ys xs
{-# 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 s = go s
    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 cs0 = rev Empty cs0
  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' v =
          S.unsafeCreate (2*l) $ \p' -> withForeignPtr fp $ \p -> do
            poke p' w
            S.c_intersperse (p' `plusPtr` 1) p (fromIntegral l) w
              where
                 (fp, l) = VS.unsafeToForeignPtr0 v

-- | The 'transpose' function transposes the rows and columns of its
-- 'ByteString' argument.
transpose :: [ByteString] -> [ByteString]
transpose css = L.map (\ss -> Chunk (S.pack ss) Empty)
                      (L.transpose (L.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 z = go z
  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 z = go z
  where go a _ | a `seq` False = undefined
        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 z cs = foldrChunks (flip (S.foldr k)) z cs
{-# INLINE foldr #-}

-- | 'foldl1' is a variant of 'foldl' that has no starting value
-- argument, and thus must be applied to non-empty 'ByteStrings'.
-- This function is subject to array fusion.
foldl1 :: (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' :: (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 :: (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 css0 = to css0
  where
    go Empty        css = to css
    go (Chunk c cs) css = Chunk c (go cs css)
    to []               = Empty
    to (cs:css)         = go cs css

-- | 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 cs = foldrChunks (\c rest -> S.any f c || rest) False cs
{-# INLINE any #-}
-- todo fuse

-- | /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 cs = foldrChunks (\c rest -> S.all f c && rest) True cs
{-# INLINE all #-}
-- todo fuse

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

-- | 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 s0 cs0 = go s0 cs0
  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 s0 cs0 = go s0 cs0
  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. This function will fuse.
--
-- > scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
--
-- Note that
--
-- > last (scanl f z xs) == foldl f z xs.
scanl :: (Word8 -> Word8 -> Word8) -> Word8 -> ByteString -> ByteString
scanl f z = snd . foldl k (z,singleton z)
 where
    k (c,acc) a = let n = f c a in (n, acc `snoc` n)
{-# INLINE scanl #-}

-- ---------------------------------------------------------------------
-- 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' -> x' `seq` 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 :: 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 s0 = unfoldChunk 32 s0
  where unfoldChunk n s =
          case S.unfoldrN n f s of
            (c, Nothing)
              | S.null c  -> Empty
              | otherwise -> Chunk c Empty
            (c, Just s')  -> Chunk c (unfoldChunk (n*2) s')

-- ---------------------------------------------------------------------
-- 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(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\/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'')


-- | 'takeWhile', applied to a predicate @p@ and a ByteString @xs@,
-- returns the longest prefix (possibly empty) of @xs@ of elements that
-- satisfy @p@.
takeWhile :: (Word8 -> Bool) -> ByteString -> ByteString
takeWhile f cs0 = takeWhile' cs0
  where takeWhile' Empty        = Empty
        takeWhile' (Chunk c cs) =
          case findIndexOrEnd (not . f) c of
            0                  -> Empty
            n | n < S.length c -> Chunk (S.take n c) Empty
              | otherwise      -> Chunk c (takeWhile' cs)

-- | 'dropWhile' @p xs@ returns the suffix remaining after 'takeWhile' @p xs@.
dropWhile :: (Word8 -> Bool) -> ByteString -> ByteString
dropWhile f cs0 = dropWhile' cs0
  where dropWhile' Empty        = Empty
        dropWhile' (Chunk c cs) =
          case findIndexOrEnd (not . f) c of
            n | n < S.length c -> Chunk (S.drop n c) cs
              | otherwise      -> dropWhile' cs

-- | 'break' @p@ is equivalent to @'span' ('not' . p)@.
break :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
break f cs0 = break' cs0
  where break' Empty        = (Empty, Empty)
        break' (Chunk c cs) =
          case findIndexOrEnd 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'')

--
-- 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 (=='c') "abcd" == breakByte 'c' "abcd"
--
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  (=='c') "abcd" == spanByte 'c' "abcd"
--
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)
-}

-- | 'span' @p xs@ breaks the ByteString into two segments. It is
-- equivalent to @('takeWhile' p xs, 'dropWhile' p xs)@
span :: (Word8 -> Bool) -> ByteString -> (ByteString, ByteString)
span p = break (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 (=='a') "aabbaca" == ["","","bb","c",""]
-- > splitWith (=='a') []        == []
--
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 '\n' "a\nb\nd\ne" == ["a","b","d","e"]
-- > split 'a'  "aXaXaXa"    == ["","X","X","X",""]
-- > split 'x'  "x"          == ["",""]
--
-- 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 'ByteStrings' 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 #-}

{-
-- | Like 'splitWith', except that sequences of adjacent separators are
-- treated as a single separator. eg.
--
-- > tokens (=='a') "aabbaca" == ["bb","c"]
--
tokens :: (Word8 -> Bool) -> ByteString -> [ByteString]
tokens f = L.filter (not.null) . splitWith f
-}

-- | 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 Empty          = []
group (Chunk c0 cs0) = group' [] (S.group c0) cs0
  where
    group' :: [P.ByteString] -> [P.ByteString] -> ByteString -> [ByteString]
    group' acc@(s':_) ss@(s:_) cs
      | S.unsafeHead s'
     /= S.unsafeHead s             = revNonEmptyChunks    acc  : group' [] ss cs
    group' acc (s:[]) Empty        = revNonEmptyChunks (s:acc) : []
    group' acc (s:[]) (Chunk c cs) = group' (s:acc) (S.group c) cs
    group' acc (s:ss) cs           = revNonEmptyChunks (s:acc) : group' [] ss cs

{-
TODO: check if something like this might be faster

group :: ByteString -> [ByteString]
group xs
    | null xs   = []
    | otherwise = ys : group zs
    where
        (ys, zs) = spanByte (unsafeHead xs) xs
-}

-- | The 'groupBy' function is the non-overloaded version of 'group'.
--
groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
groupBy _ Empty          = []
groupBy k (Chunk c0 cs0) = groupBy' [] 0 (S.groupBy k c0) cs0
  where
    groupBy' :: [P.ByteString] -> Word8 -> [P.ByteString] -> ByteString -> [ByteString]
    groupBy' acc@(_:_) c ss@(s:_) cs
      | not (c `k` S.unsafeHead s)     = revNonEmptyChunks acc : groupBy' [] 0 ss cs
    groupBy' acc _ (s:[]) Empty        = revNonEmptyChunks (s : acc) : []
    groupBy' acc w (s:[]) (Chunk c cs) = groupBy' (s:acc) w' (S.groupBy k c) cs
                                           where w' | L.null acc = S.unsafeHead s
                                                    | otherwise  = w
    groupBy' acc _ (s:ss) cs           = revNonEmptyChunks (s : acc) : groupBy' [] 0 ss cs

{-
TODO: check if something like this might be faster

groupBy :: (Word8 -> Word8 -> Bool) -> ByteString -> [ByteString]
groupBy k xs
    | null xs   = []
    | otherwise = take n xs : groupBy k (drop n xs)
    where
        n = 1 + findIndexOrEnd (not . k (head xs)) (tail xs)
-}

-- | /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 . (L.intersperse s)

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

-- | /O(c)/ 'ByteString' index (subscript) operator, starting from 0.
index :: 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(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 cs0 = elemIndex' 0 cs0
  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 ==
-- > (-) (length xs - 1) `fmap` elemIndex c (reverse xs)
--
elemIndexEnd :: Word8 -> ByteString -> Maybe Int
elemIndexEnd ch (PS x s l) = inlinePerformIO $ withForeignPtr x $ \p ->
    go (p `plusPtr` s) (l-1)
  where
    go !p !i | i < 0     = return Nothing
             | otherwise = do ch' <- peekByteOff p i
                              if ch == ch'
                                then return $ Just i
                                else go p (i-1)
-}
-- | /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 cs0 = elemIndices' 0 cs0
  where elemIndices' _ Empty        = []
        elemIndices' n (Chunk c cs) = L.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 cs = foldlChunks (\n c -> n + fromIntegral (S.count w c)) 0 cs

-- | 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 cs0 = findIndex' 0 cs0
  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 #-}

-- | /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 cs0 = find' cs0
  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 cs0 = findIndices' 0 cs0
  where findIndices' _ Empty        = []
        findIndices' n (Chunk c cs) = L.map ((+n).fromIntegral) (S.findIndices k c)
                             ++ findIndices' (n + fromIntegral (S.length c)) cs

-- ---------------------------------------------------------------------
-- 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 (elem w 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 s = go s
    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 f p = (filter f p, filter (not . f) p)
--TODO: use a better implementation

-- ---------------------------------------------------------------------
-- 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 '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

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

-- | /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 (L.map fst ls), pack (L.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) = L.map (\c' -> Chunk c' Empty) (L.tail (S.inits c))
                           ++ L.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 cs = foldrChunks (Chunk . S.copy) Empty cs
--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.
--
-- Note: the 'Handle' should be placed in binary mode with
-- 'System.IO.hSetBinaryMode' for 'hGetContentsN' to
-- work correctly.
--
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 do hClose h >> return Empty
          else do cs <- lazyRead
                  return (Chunk c cs)

-- | 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.
--
-- Once EOF is encountered, the Handle is closed.
--
-- Note: the 'Handle' should be placed in binary mode with
-- 'System.IO.hSetBinaryMode' for 'hGetContents' to
-- work correctly.
--
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.
--
readFile :: FilePath -> IO ByteString
readFile f = openBinaryFile f ReadMode >>= hGetContents

-- | Write a 'ByteString' to a file.
--
writeFile :: FilePath -> ByteString -> IO ()
writeFile f txt = bracket (openBinaryFile f WriteMode) hClose
    (\hdl -> hPut hdl txt)

-- | Append a 'ByteString' to a file.
--
appendFile :: FilePath -> ByteString -> IO ()
appendFile f txt = bracket (openBinaryFile f AppendMode) hClose
    (\hdl -> hPut hdl txt)

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

-- | Outputs a 'ByteString' to the specified 'Handle'.
--
hPut :: Handle -> ByteString -> IO ()
hPut h cs = foldrChunks (\c rest -> S.hPut h c >> rest) (return ()) cs

-- | 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

-- | Write a ByteString to stdout, appending a newline byte
--
putStrLn :: ByteString -> IO ()
putStrLn ps = hPut stdout ps >> hPut stdout (singleton 0x0a)

{-# DEPRECATED putStrLn
    "Use Data.ByteString.Lazy.Char8.putStrLn instead. (Functions that rely on ASCII encodings belong in Data.ByteString.Lazy.Char8)"
  #-}

-- | 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 :: String -> a
errorEmptyList fun = moduleError fun "empty ByteString"

moduleError :: String -> String -> a
moduleError fun msg = error ("Data.Vector.Storable.ByteString.Lazy." ++ fun ++ ':':' ':msg)


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

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

-- | 'findIndexOrEnd' is a variant of findIndex, that returns the length
-- of the string if no element is found, rather than Nothing.
findIndexOrEnd :: (Word8 -> Bool) -> P.ByteString -> Int
findIndexOrEnd k v = S.inlinePerformIO $ withForeignPtr fp $ \f -> go f 0
  where
    (fp, l) = VS.unsafeToForeignPtr0 v

    go !ptr !n | n >= l    = return l
               | otherwise = do w <- peek ptr
                                if k w
                                  then return n
                                  else go (ptr `plusPtr` 1) (n+1)
{-# INLINE findIndexOrEnd #-}