{-# LANGUAGE BangPatterns #-}
-- |
-- Module      : Data.Massiv.Array.Ops.Slice
-- Copyright   : (c) Alexey Kuleshevich 2018-2019
-- License     : BSD3
-- Maintainer  : Alexey Kuleshevich <lehins@yandex.ru>
-- Stability   : experimental
-- Portability : non-portable
--
module Data.Massiv.Array.Ops.Slice
  (
  -- ** From the outside
    (!>)
  , (!?>)
  , (??>)
  -- ** From the inside
  , (<!)
  , (<!?)
  , (<??)
  -- ** From within
  , (<!>)
  , (<!?>)
  , (<??>)
  ) where

import Control.Monad (unless)
import Data.Massiv.Core.Common


infixl 4 !>, !?>, ??>, <!, <!?, <??, <!>, <!?>, <??>


-- | /O(1)/ - Slices the array from the outside. For 2-dimensional array this will
-- be equivalent of taking a row. Throws an error when index is out of bounds.
--
-- ===__Examples__
--
-- You could say that slicing from outside is synonymous to slicing from the end or slicing at the
-- highermost dimension. For example with rank-3 arrays outer slice would be equivalent to getting a
-- page:
--
-- >>> import Data.Massiv.Array
-- >>> arr = makeArrayR U Seq (Sz (3 :> 2 :. 4)) fromIx3
-- >>> arr
-- Array U Seq (Sz (3 :> 2 :. 4))
--   [ [ [ (0,0,0), (0,0,1), (0,0,2), (0,0,3) ]
--     , [ (0,1,0), (0,1,1), (0,1,2), (0,1,3) ]
--     ]
--   , [ [ (1,0,0), (1,0,1), (1,0,2), (1,0,3) ]
--     , [ (1,1,0), (1,1,1), (1,1,2), (1,1,3) ]
--     ]
--   , [ [ (2,0,0), (2,0,1), (2,0,2), (2,0,3) ]
--     , [ (2,1,0), (2,1,1), (2,1,2), (2,1,3) ]
--     ]
--   ]
-- >>> arr !> 2
-- Array M Seq (Sz (2 :. 4))
--   [ [ (2,0,0), (2,0,1), (2,0,2), (2,0,3) ]
--   , [ (2,1,0), (2,1,1), (2,1,2), (2,1,3) ]
--   ]
--
-- There is nothing wrong with chaining, mixing and matching slicing operators, or even using them
-- to index arrays:
--
-- >>> arr !> 2 !> 0 !> 3
-- (2,0,3)
-- >>> arr !> 2 <! 3 ! 0
-- (2,0,3)
-- >>> (arr !> 2 !> 0 !> 3) == (arr ! 2 :> 0 :. 3)
-- True
--
--
-- @since 0.1.0
(!>) :: OuterSlice r ix e => Array r ix e -> Int -> Elt r ix e
(!>) !arr !ix = either throw id (arr !?> ix)
{-# INLINE (!>) #-}


-- | /O(1)/ - Just like `!>` slices the array from the outside, but returns
-- `Nothing` when index is out of bounds.
--
-- @since 0.1.0
(!?>) :: (MonadThrow m, OuterSlice r ix e) => Array r ix e -> Int -> m (Elt r ix e)
(!?>) !arr !i
  | isSafeIndex sz i = pure $ unsafeOuterSlice arr i
  | otherwise = throwM $ IndexOutOfBoundsException sz i
  where
    !sz = fst (unconsSz (size arr))
{-# INLINE (!?>) #-}


-- | /O(1)/ - Safe slicing continuation from the outside. Similarly to (`!>`) slices the array from
-- the outside, but takes `Maybe` array as input and returns `Nothing` when index is out of bounds.
--
-- ===__Examples__
--
-- >>> import Data.Massiv.Array
-- >>> arr = makeArrayR U Seq (Sz (3 :> 2 :. 4)) fromIx3
-- >>> arr !?> 2 ??> 0 ??> 3 :: Maybe Ix3T
-- Just (2,0,3)
-- >>> arr !?> 2 ??> 0 ??> -1 :: Maybe Ix3T
-- Nothing
-- >>> arr !?> 2 ??> -10 ?? 1
-- *** Exception: IndexOutOfBoundsException: -10 not safe for (Sz1 2)
--
-- @since 0.1.0
(??>) :: (MonadThrow m, OuterSlice r ix e) => m (Array r ix e) -> Int -> m (Elt r ix e)
(??>) marr !ix = marr >>= (!?> ix)
{-# INLINE (??>) #-}


-- | /O(1)/ - Safe slice from the inside
--
-- @since 0.1.0
(<!?) :: (MonadThrow m, InnerSlice r ix e) => Array r ix e -> Int -> m (Elt r ix e)
(<!?) !arr !i
  | isSafeIndex m i = pure $ unsafeInnerSlice arr sz i
  | otherwise = throwM $ IndexOutOfBoundsException m i
  where
    !sz@(_, m) = unsnocSz (size arr)
{-# INLINE (<!?) #-}


-- | /O(1)/ - Similarly to (`!>`) slice an array from an opposite direction.
--
-- @since 0.1.0
(<!) :: InnerSlice r ix e => Array r ix e -> Int -> Elt r ix e
(<!) !arr !ix =
  case arr <!? ix of
    Right res -> res
    Left exc  -> throw exc
{-# INLINE (<!) #-}


-- | /O(1)/ - Safe slicing continuation from the inside
--
-- @since 0.1.0
(<??) :: (MonadThrow m, InnerSlice r ix e) => m (Array r ix e) -> Int -> m (Elt r ix e)
(<??) marr !ix = marr >>= (<!? ix)
{-# INLINE (<??) #-}


-- | /O(1)/ - Same as (`<!>`), but fails gracefully with a `Nothing`, instead of an error
--
-- @since 0.1.0
(<!?>) :: (MonadThrow m, Slice r ix e) => Array r ix e -> (Dim, Int) -> m (Elt r ix e)
(<!?>) !arr (dim, i) = do
  (m, szl) <- pullOutSzM (size arr) dim
  unless (isSafeIndex m i) $ throwM $ IndexOutOfBoundsException m i
  start <- setDimM zeroIndex dim i
  cutSz <- insertSzM szl dim oneSz
  unsafeSlice arr start cutSz dim
{-# INLINE (<!?>) #-}


-- prop> arr !> i == arr <!> (dimensions (size arr), i)
-- prop> arr <! i == arr <!> (1,i)
--
-- | /O(1)/ - Slices the array in any available dimension. Throws an error when
-- index is out of bounds or dimensions is invalid.
--
-- @since 0.1.0
(<!>) :: Slice r ix e => Array r ix e -> (Dim, Int) -> Elt r ix e
(<!>) !arr !dix =
  case arr <!?> dix of
    Right res -> res
    Left exc  -> throw exc
{-# INLINE (<!>) #-}


-- | /O(1)/ - Safe slicing continuation from within.
--
-- @since 0.1.0
(<??>) :: (MonadThrow m, Slice r ix e) => m (Array r ix e) -> (Dim, Int) -> m (Elt r ix e)
(<??>) !marr !ix = marr >>= (<!?> ix)
{-# INLINE (<??>) #-}