{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
{-
	Copyright (C) 2018 Dr. Alistair Ward

	This file is part of BishBosh.

	BishBosh is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	BishBosh is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with BishBosh.  If not, see <http://www.gnu.org/licenses/>.
-}
{- |
 [@AUTHOR@]	Dr. Alistair Ward

 [@DESCRIPTION@]	Defines the file on which an En-passant option currently exists.
-}

module BishBosh.State.EnPassantAbscissa (
-- * Types
-- ** Data-types
	EnPassantAbscissa(getAbscissa),
-- * Functions
-- ** Constructor
	mkMaybeEnPassantAbscissa
) where

import qualified	BishBosh.Attribute.LogicalColour	as Attribute.LogicalColour
import qualified	BishBosh.Cartesian.Coordinates		as Cartesian.Coordinates
import qualified	BishBosh.Component.Move			as Component.Move
import qualified	BishBosh.Component.Piece		as Component.Piece
import qualified	BishBosh.Component.QualifiedMove	as Component.QualifiedMove
import qualified	BishBosh.Component.Turn			as Component.Turn
import qualified	BishBosh.Component.Zobrist		as Component.Zobrist
import qualified	BishBosh.Property.Opposable		as Property.Opposable
import qualified	BishBosh.State.MaybePieceByCoordinates	as State.MaybePieceByCoordinates
import qualified	Control.DeepSeq
import qualified	Data.Array.IArray
import qualified	Data.Maybe

-- | Defines the file on which an En-passant option currently exists.
newtype EnPassantAbscissa x	= MkEnPassantAbscissa {
	getAbscissa	:: x	-- ^ The file on which an En-passant option currently exists.
} deriving (Eq, Ord)

instance Data.Array.IArray.Ix x => Component.Zobrist.Hashable1D EnPassantAbscissa x {-CAVEAT: FlexibleInstances, MultiParamTypeClasses-} where
	listRandoms1D MkEnPassantAbscissa { getAbscissa = x }	= return {-to List-monad-} . Component.Zobrist.dereferenceRandomByEnPassantAbscissa x

instance Control.DeepSeq.NFData x => Control.DeepSeq.NFData (EnPassantAbscissa x) where
	rnf MkEnPassantAbscissa { getAbscissa = x }	= Control.DeepSeq.rnf x

-- | Constructor.
mkMaybeEnPassantAbscissa :: (
	Enum	x,
	Enum	y,
	Ord	x,
	Ord	y
 )
	=> Attribute.LogicalColour.LogicalColour	-- ^ The player who moves next, & who may have an En-passant option.
	-> State.MaybePieceByCoordinates.MaybePieceByCoordinates x y
	-> Component.Turn.Turn x y			-- ^ The last /turn/ taken.
	-> Maybe (EnPassantAbscissa x)
mkMaybeEnPassantAbscissa nextLogicalColour maybePieceByCoordinates lastTurn
	| Component.Turn.isPawnDoubleAdvance (Property.Opposable.getOpposite nextLogicalColour) lastTurn
	, let destination	= Component.Move.getDestination . Component.QualifiedMove.getMove $ Component.Turn.getQualifiedMove lastTurn
	, any (
		Data.Maybe.maybe False {-unoccupied-} (
			== Component.Piece.mkPawn nextLogicalColour
		) . (
			`State.MaybePieceByCoordinates.dereference` maybePieceByCoordinates
		)
	) $ Cartesian.Coordinates.getAdjacents destination	= Just . MkEnPassantAbscissa $ Cartesian.Coordinates.getX destination
	| otherwise						= Nothing