{-# LANGUAGE BangPatterns, ExistentialQuantification #-}
-- |
-- Module      : Data.Text.Internal.Fusion.Types
-- Copyright   : (c) Tom Harper 2008-2009,
--               (c) Bryan O'Sullivan 2009,
--               (c) Duncan Coutts 2009,
--               (c) Jasper Van der Jeugt 2011
--
-- License     : BSD-style
-- Maintainer  : bos@serpentine.com
-- Stability   : experimental
-- Portability : GHC
--
-- /Warning/: this is an internal module, and does not have a stable
-- API or name. Functions in this module may not check or enforce
-- preconditions expected by public modules. Use at your own risk!
--
-- Core stream fusion functionality for text.

module Data.Text.Internal.Fusion.Types
    (
      CC(..)
    , PairS(..)
    , Scan(..)
    , RS(..)
    , Step(..)
    , Stream(..)
    , empty
    ) where

import Data.Text.Internal.Fusion.Size
import Data.Word (Word8)

-- | Specialised tuple for case conversion.
data CC s = CC !s {-# UNPACK #-} !Char {-# UNPACK #-} !Char

-- | Restreaming state.
data RS s
    = RS0 !s
    | RS1 !s {-# UNPACK #-} !Word8
    | RS2 !s {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8
    | RS3 !s {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8 {-# UNPACK #-} !Word8

-- | Strict pair.
data PairS a b = !a :*: !b
                 -- deriving (Eq, Ord, Show)
infixl 2 :*:

-- | An intermediate result in a scan.
data Scan s = Scan1 {-# UNPACK #-} !Char !s
            | Scan2 {-# UNPACK #-} !Char !s

-- | Intermediate result in a processing pipeline.
data Step s a = Done
              | Skip !s
              | Yield !a !s

{-
instance (Show a) => Show (Step s a)
    where show Done        = "Done"
          show (Skip _)    = "Skip"
          show (Yield x _) = "Yield " ++ show x
-}

instance (Eq a) => Eq (Stream a) where
    == :: Stream a -> Stream a -> Bool
(==) = forall a. Eq a => Stream a -> Stream a -> Bool
eq

instance (Ord a) => Ord (Stream a) where
    compare :: Stream a -> Stream a -> Ordering
compare = forall a. Ord a => Stream a -> Stream a -> Ordering
cmp

-- The length hint in a Stream has two roles.  If its value is zero,
-- we trust it, and treat the stream as empty.  Otherwise, we treat it
-- as a hint: it should usually be accurate, so we use it when
-- unstreaming to decide what size array to allocate.  However, the
-- unstreaming functions must be able to cope with the hint being too
-- small or too large.
--
-- The size hint tries to track the UTF-16 code units in a stream,
-- but often counts the number of code points instead.  It can easily
-- undercount if, for instance, a transformed stream contains astral
-- plane code points (those above 0x10000).

data Stream a =
    forall s. Stream
    (s -> Step s a)             -- stepper function
    !s                          -- current state
    !Size                       -- size hint in code units

-- | /O(n)/ Determines if two streams are equal.
eq :: (Eq a) => Stream a -> Stream a -> Bool
eq :: forall a. Eq a => Stream a -> Stream a -> Bool
eq (Stream s -> Step s a
next1 s
s1 Size
_) (Stream s -> Step s a
next2 s
s2 Size
_) = Step s a -> Step s a -> Bool
loop (s -> Step s a
next1 s
s1) (s -> Step s a
next2 s
s2)
    where
      loop :: Step s a -> Step s a -> Bool
loop Step s a
Done Step s a
Done                     = Bool
True
      loop (Skip s
s1')     (Skip s
s2')     = Step s a -> Step s a -> Bool
loop (s -> Step s a
next1 s
s1') (s -> Step s a
next2 s
s2')
      loop (Skip s
s1')     Step s a
x2             = Step s a -> Step s a -> Bool
loop (s -> Step s a
next1 s
s1') Step s a
x2
      loop Step s a
x1             (Skip s
s2')     = Step s a -> Step s a -> Bool
loop Step s a
x1          (s -> Step s a
next2 s
s2')
      loop Step s a
Done Step s a
_                        = Bool
False
      loop Step s a
_    Step s a
Done                     = Bool
False
      loop (Yield a
x1 s
s1') (Yield a
x2 s
s2') = a
x1 forall a. Eq a => a -> a -> Bool
== a
x2 Bool -> Bool -> Bool
&&
                                           Step s a -> Step s a -> Bool
loop (s -> Step s a
next1 s
s1') (s -> Step s a
next2 s
s2')
{-# INLINE [0] eq #-}

cmp :: (Ord a) => Stream a -> Stream a -> Ordering
cmp :: forall a. Ord a => Stream a -> Stream a -> Ordering
cmp (Stream s -> Step s a
next1 s
s1 Size
_) (Stream s -> Step s a
next2 s
s2 Size
_) = Step s a -> Step s a -> Ordering
loop (s -> Step s a
next1 s
s1) (s -> Step s a
next2 s
s2)
    where
      loop :: Step s a -> Step s a -> Ordering
loop Step s a
Done Step s a
Done                     = Ordering
EQ
      loop (Skip s
s1')     (Skip s
s2')     = Step s a -> Step s a -> Ordering
loop (s -> Step s a
next1 s
s1') (s -> Step s a
next2 s
s2')
      loop (Skip s
s1')     Step s a
x2             = Step s a -> Step s a -> Ordering
loop (s -> Step s a
next1 s
s1') Step s a
x2
      loop Step s a
x1             (Skip s
s2')     = Step s a -> Step s a -> Ordering
loop Step s a
x1          (s -> Step s a
next2 s
s2')
      loop Step s a
Done Step s a
_                        = Ordering
LT
      loop Step s a
_    Step s a
Done                     = Ordering
GT
      loop (Yield a
x1 s
s1') (Yield a
x2 s
s2') =
          case forall a. Ord a => a -> a -> Ordering
compare a
x1 a
x2 of
            Ordering
EQ    -> Step s a -> Step s a -> Ordering
loop (s -> Step s a
next1 s
s1') (s -> Step s a
next2 s
s2')
            Ordering
other -> Ordering
other
{-# INLINE [0] cmp #-}

-- | The empty stream.
empty :: Stream a
empty :: forall a. Stream a
empty = forall a s. (s -> Step s a) -> s -> Size -> Stream a
Stream forall {p} {s} {a}. p -> Step s a
next () Size
0
    where next :: p -> Step s a
next p
_ = forall s a. Step s a
Done
{-# INLINE [0] empty #-}