module Store(

    ElemIndex(),

    MStore(),

    IStore(),

    newStore,

    addElem,

    removeElem,

    readElem,

    writeElem,

    modifyElem,

    firstIndex,

    withIStore,

    withIStore2,

    (!),

    indices

    ) where

import qualified Data.Array.IArray as IA

import qualified Data.Array.IO as IOA

import qualified Data.IntSet as IntSet

import Data.IORef

import Control.Monad

newtype ElemIndex = ElemIndex Int

    deriving (Eq)

newtype MStore e = MStore (IORef (IntSet.IntSet, IntSet.IntSet, IOA.IOArray Int e))

newtype IStore e = IStore (IntSet.IntSet, IA.Array Int e)

instance Show ElemIndex where

    show (ElemIndex i) = 'i' : show i

firstIndex :: ElemIndex

firstIndex = ElemIndex 0

-- MStore code

initialSize :: Int

initialSize = 10

growFunc :: Int -> Int

growFunc a = a * 3 `div` 2

newStore :: IO (MStore e)

newStore = do

    newar <- IOA.newArray_ (0, initialSize - 1)

    new <- newIORef (IntSet.empty, IntSet.fromAscList [0..initialSize - 1], newar)

    return (MStore new)

growStore :: MStore e -> IO ()

growStore (MStore ref) = do

    (busyElems, freeElems, arr) <- readIORef ref

    (_, m') <- IOA.getBounds arr

    let newM' = growFunc (m' + 1) - 1

    newArr <- IOA.newArray_ (0, newM')

    sequence_ [IOA.readArray arr i >>= IOA.writeArray newArr i | i <- [0..m']]

    writeIORef ref (busyElems, freeElems `IntSet.union` (IntSet.fromAscList [m'+1..newM']), newArr)

growIfNeeded :: MStore e -> IO ()

growIfNeeded m@(MStore ref) = do

    (_, freeElems, _) <- readIORef ref

    when (IntSet.null freeElems) $ growStore m

addElem :: MStore e -> e -> IO ElemIndex

addElem m@(MStore ref) element = do

    growIfNeeded m

    (busyElems, freeElems, arr) <- readIORef ref

    let (n, freeElems') = IntSet.deleteFindMin freeElems

    IOA.writeArray arr n element

    writeIORef ref (IntSet.insert n busyElems, freeElems', arr)

    return $ ElemIndex n

removeElem :: MStore e -> ElemIndex -> IO ()

removeElem (MStore ref) (ElemIndex n) = do

    (busyElems, freeElems, arr) <- readIORef ref

    IOA.writeArray arr n undefined

    writeIORef ref (IntSet.delete n busyElems, IntSet.insert n freeElems, arr)

readElem :: MStore e -> ElemIndex -> IO e

readElem (MStore ref) (ElemIndex n) = readIORef ref >>= \(_, _, arr) -> IOA.readArray arr n

writeElem :: MStore e -> ElemIndex -> e -> IO ()

writeElem (MStore ref) (ElemIndex n) el = readIORef ref >>= \(_, _, arr) -> IOA.writeArray arr n el

modifyElem :: MStore e -> (e -> e) -> ElemIndex -> IO ()

modifyElem (MStore ref) f (ElemIndex n) = do

    (_, _, arr) <- readIORef ref

    IOA.readArray arr n >>= (IOA.writeArray arr n) . f

-- A way to use see MStore elements in pure code via IStore

m2i :: MStore e -> IO (IStore e)

m2i (MStore ref) = do

    (a, _, c') <- readIORef ref 

    c <- IOA.unsafeFreeze c'

    return $ IStore (a, c)

withIStore :: MStore e -> (IStore e -> a) -> IO a

withIStore m f = liftM f (m2i m)

withIStore2 :: MStore e1 -> MStore e2 -> (IStore e1 -> IStore e2 -> a) -> IO a

withIStore2 m1 m2 f = do

    i1 <- m2i m1

    i2 <- m2i m2

    return $ f i1 i2

-- IStore code

(!) :: IStore e -> ElemIndex -> e

(!) (IStore (_, arr)) (ElemIndex i) = (IA.!) arr i

indices :: IStore e -> [ElemIndex]

indices (IStore (busy, _)) = map ElemIndex $ IntSet.toList busy