//**** Defines used to model the extra Pawn moves. ****
(define "SetEnPassantLocation"
    (then 
        (set Pending (ahead (last To) Backward))
    )
)

(define "InLocationEnPassant"
    (and 
        (is Pending) 
        (= (to) (value Pending)) 
    )
)

(define "EnPassant"
    (move Step 
        (directions {FR FL}) 
        (to if:"InLocationEnPassant") 
        (then 
            (remove 
                (ahead (last To) Backward)
            )
        )
    )
)

(define "InitialPawnMove"
    (if (is In (from) (sites Start (piece (what at:(from)))))
        ("DoubleStepForwardToEmpty" "SetEnPassantLocation")
    )
)

//------------------------------------------------------------------------------

(game "The Pawn Game" // Cross The Board
    ("TwoPlayersNorthSouth") 
    (equipment { 
        (board (square 8))
        ("ChessPawn" "Pawn"
            (or 
                "InitialPawnMove"
                "EnPassant"
            )
        )
        <Variant:piece>
        (regions P1 (sites Top))
        (regions P2 (sites Bottom))
    }) 
    (rules 
        (start { 
            (place "Pawn1" (sites Row 1))
            (place "Pawn2" (sites Row 6))
            <Variant:startP1>
            <Variant:startP2>
        })
        
        (play (forEach Piece))
        
        (end {
            ("ReachWin" (sites Mover) Mover)
            ("BlockWin")
            <Variant:end>
        }) 
    )
)

//------------------------------------------------------------------------------

(option "Variant" <Variant> args:{ <piece> <startP1> <startP2> <end> }
    {
    (item "Only Pawn" <> <> <> <> "The game is played with only pawns.")* 
    (item "Rooks" <("ChessRook" "Rook")> <(place "Rook1" {"A1" "H1"})> <(place "Rook2" {"A8" "H8"})> <> "Chess rooks are added to the game.") 
    (item "Knights" <("ChessKnight" "Knight")> <(place "Knight1" {"B1" "G1"})> <(place "Knight2" {"B8" "G8"})> <> "Chess knights are added to the game.") 
    (item "Bishops" <("ChessBishop" "Bishop")> <(place "Bishop1" {"C1" "F1"})> <(place "Bishop2" {"C8" "F8"})> <> "Chess bishops are added to the game.") 
    (item "Queens" <("ChessQueen" "Queen")> <(place "Queen1" coord:"D1")> <(place "Queen2" coord:"D8")> <> "Chess queens are added to the game.") 
    (item "Kings" <("ChessKing" "King")> <(place "King1" coord:"E1")> <(place "King2" coord:"E8")> <(if (no Pieces Enemy "King") (result Mover Win))> "Chess kings are added to the game. If you capture the king you win as well.") 
})

//------------------------------------------------------------------------------

(metadata
    
    (info
        {
        (description "This mini-game (also called the Pawn Game) gives a good feel for how the pawns move, capture and defend themselves. Pawns provide the backdrop for chess. Structures such as pawn chains will emerge as well as important concepts such as the sacrifice. To play the game well requires counting ahead as pawns race each other.")
        (aliases {"Cross The Board"})
        (rules "Each side has a line of pawns. The pawns move as in chess i.e. The pawn moves forwards one square (optionally two squares on its first move) and captures diagonally forwards one square by replacing the opponent’s piece. The rule of En Passant is also allowed. White goes first. The first person to reach the other side is the winner. You also win if it is your opponent’s move and they have no moves left.
        In Ludii, options are also available to add each of the five other Chess piece types. In the variant with the king piece, if you capture the opponent king, you win as well.")
        (id "2023")
        (source "<a href=\"https://chessplus.net/the-pawn-game/\" target=\"_blank\" class=\"style1\" style=\"color: #0000EE\" />ChessPlus</a>")
        (version "1.3.12")
        (classification "board/race/reach")
        (credit "Eric Piette")
        }
    )
    
    (graphics {
        (board Style Chess)
    })
    
    (ai
        "The Pawn Game_ai"
    )
)