{-
	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 <https://www.gnu.org/licenses/>.
-}
{- |
 [@AUTHOR@]	Dr. Alistair Ward

 [@DESCRIPTION@]	The details of a player's turn.
-}

module BishBosh.Component.Turn(
-- * Types
-- ** Data-types
        Turn(
--		MkTurn,
                getQualifiedMove,
                getRank,
                getIsRepeatableMove
        ),
-- * Functions
        compareByLVA,
        compareByMVVLVA,
-- ** Constructor
        mkTurn,
-- ** Predicates
        isCapture,
        isPawnDoubleAdvance
) where

import                  Control.Arrow((&&&))
import qualified        BishBosh.Attribute.LogicalColour        as Attribute.LogicalColour
import qualified        BishBosh.Attribute.MoveType             as Attribute.MoveType
import qualified        BishBosh.Attribute.Rank                 as Attribute.Rank
import qualified        BishBosh.Component.Move                 as Component.Move
import qualified        BishBosh.Component.QualifiedMove        as Component.QualifiedMove
import qualified        BishBosh.Property.Reflectable           as Property.Reflectable
import qualified        Control.Arrow
import qualified        Control.DeepSeq
import qualified        Data.Default
import qualified        Data.Ord

{- |
	* Defines one turn of a player.

	* Additional data is recorded to facilitate both rollback & recording of the /move/ in various conventional notations.
-}
data Turn x y   = MkTurn {
        getQualifiedMove        :: Component.QualifiedMove.QualifiedMove x y,
        getRank                 :: Attribute.Rank.Rank, -- ^ The /rank/ of /piece/ that was moved, prior to any promotion.
        getIsRepeatableMove     :: Bool                 -- ^ Whether this move can ever recur; without rolling-back.
}

instance (Eq x, Eq y) => Eq (Turn x y) where
        MkTurn {
                getQualifiedMove        = qualifiedMove,
                getRank                 = rank
        } == MkTurn {
                getQualifiedMove        = qualifiedMove',
                getRank                 = rank'
        } = (qualifiedMove, rank) == (qualifiedMove', rank')    -- 'getIsRepeatableMove' can be derived.

instance (Control.DeepSeq.NFData x, Control.DeepSeq.NFData y) => Control.DeepSeq.NFData (Turn x y) where
        rnf MkTurn {
                getQualifiedMove        = qualifiedMove,
                getRank                 = rank,
                getIsRepeatableMove     = isRepeatableMove
        } = Control.DeepSeq.rnf (qualifiedMove, rank, isRepeatableMove)

instance (Show x, Show y) => Show (Turn x y) where
        showsPrec _ MkTurn {
                getQualifiedMove        = qualifiedMove,
                getRank                 = rank
--		getIsRepeatableMove	= isRepeatableMove
        } = shows (
                qualifiedMove,
                rank
--		isRepeatableMove	-- Derived.
         ) -- Represent as a tuple.

instance (
        Enum    x,
        Enum    y,
        Ord     x,
        Ord     y,
        Read    x,
        Read    y
 ) => Read (Turn x y) where
        readsPrec _     = map (Control.Arrow.first $ uncurry mkTurn) . reads

instance Enum y => Property.Reflectable.ReflectableOnX (Turn x y) where
        reflectOnX turn@MkTurn { getQualifiedMove = qualifiedMove } = turn { getQualifiedMove = Property.Reflectable.reflectOnX qualifiedMove }

-- | Smart constructor.
mkTurn
        :: Component.QualifiedMove.QualifiedMove x y
        -> Attribute.Rank.Rank
        -> Turn x y
mkTurn qualifiedMove rank = MkTurn {
        getQualifiedMove        = qualifiedMove,
        getRank                 = rank,
        getIsRepeatableMove     = rank /= Attribute.Rank.Pawn {-can't retreat-} && not (
                Attribute.MoveType.isAcyclic $ Component.QualifiedMove.getMoveType qualifiedMove
        ) -- Infer.
}

-- | Convenience.
isCapture :: Turn x y -> Bool
isCapture MkTurn { getQualifiedMove = qualifiedMove }   = Attribute.MoveType.isCapture $ Component.QualifiedMove.getMoveType qualifiedMove

-- | Whether the /turn/ represents a @Pawn@'s initial two-square advance.
isPawnDoubleAdvance :: (
        Enum    x,
        Enum    y,
        Eq      y
 )
        => Attribute.LogicalColour.LogicalColour        -- Defines the side whose /turn/ is referenced.
        -> Turn x y
        -> Bool
isPawnDoubleAdvance logicalColour MkTurn {
        getRank                 = Attribute.Rank.Pawn,
        getQualifiedMove        = qualifiedMove
} = Component.Move.isPawnDoubleAdvance logicalColour (Component.QualifiedMove.getMove qualifiedMove) && Component.QualifiedMove.getMoveType qualifiedMove == Data.Default.def
isPawnDoubleAdvance _ _ = False

-- | Forwards the request to 'Attribute.Rank.compareByLVA'.
compareByLVA
        :: Ord rankValue
        => Attribute.Rank.EvaluateRank rankValue
        -> Turn x y
        -> Turn x y
        -> Ordering
compareByLVA evaluateRank MkTurn { getRank = rankL } MkTurn { getRank = rankR } = Attribute.Rank.compareByLVA evaluateRank rankL rankR

{- |
	* Compares /turn/s by <https://chessprogramming.wikispaces.com/MVV-LVA>.

	* This orders the most valuable victim of an attack first, but when victims are of equal rank, orders the least valuable aggressor first.

	* N.B.: the order of non-capture moves (including promotions) isn't defined.

	* CAVEAT: no account is made for any defenders of the attacked piece, which might recoup transient gains.
-}
compareByMVVLVA
        :: Ord rankValue
        => Attribute.Rank.EvaluateRank rankValue
        -> Turn x y
        -> Turn x y
        -> Ordering
compareByMVVLVA evaluateRank turnL@MkTurn {
        getQualifiedMove        = qualifiedMoveL
} turnR@MkTurn {
        getQualifiedMove        = qualifiedMoveR
} = case ($ qualifiedMoveL) &&& ($ qualifiedMoveR) $ Attribute.MoveType.getMaybeImplicitlyTakenRank . Component.QualifiedMove.getMoveType of
        (Nothing, Nothing)      -> EQ
        (Nothing, _)            -> GT
        (_, Nothing)            -> LT
        (Just rankL, Just rankR)
                | rankL == rankR        -> lvaComparison
                | otherwise             -> case Data.Ord.comparing evaluateRank rankR rankL {-MVV-} of
                        EQ              -> lvaComparison
                        ordering        -> ordering     -- MVV-comparison uniquely defines the order.
        where
                lvaComparison   = compareByLVA evaluateRank turnL turnR