mchess-server/chess/pawn.go

package chess

import (
	"mchess_server/types"

	"github.com/samber/lo"
)

type Pawn struct {
	Color types.ChessColor
}

func (p Pawn) GetAllMovesButBlocked(board Board, fromSquare types.Coordinate) []types.Coordinate {
	theoreticalSquares := p.getAllMoves(fromSquare)
	legalSquares := p.filterBlockedSquares(board, fromSquare, theoreticalSquares)

	return legalSquares
}

func (p Pawn) GetColor() types.ChessColor {
	return p.Color
}

func (p Pawn) getAllMoves(fromSquare types.Coordinate) []types.Coordinate {
	theoreticalMoves := make([]types.Coordinate, 0, 4)

	switch p.Color {
	case types.Black:
		firstMove := fromSquare.Row == types.RangeLastValid-1
		
        if fromSquare.Down(1) != nil {
			theoreticalMoves = append(theoreticalMoves, *fromSquare.Down(1))
		}
		if firstMove && fromSquare.Down(2) != nil {
			theoreticalMoves = append(theoreticalMoves, *fromSquare.Down(2))
		}

		if lowerRight := fromSquare.Down(1).Right(1); lowerRight != nil {
			theoreticalMoves = append(theoreticalMoves, *lowerRight)
		}
		if lowerLeft := fromSquare.Down(1).Left(1); lowerLeft != nil {
			theoreticalMoves = append(theoreticalMoves, *lowerLeft)
		}

	case types.White:
		firstMove := fromSquare.Row == types.RangeFirstValid+1

		if fromSquare.Up(1) != nil {
			theoreticalMoves = append(theoreticalMoves, *fromSquare.Up(1))
		}
		if firstMove && fromSquare.Up(2) != nil {
			theoreticalMoves = append(theoreticalMoves, *fromSquare.Up(2))
		}

		if upperRight := fromSquare.Up(1).Right(1); upperRight != nil {
			theoreticalMoves = append(theoreticalMoves, *upperRight)
		}
		if upperLeft := fromSquare.Up(1).Left(1); upperLeft != nil {
			theoreticalMoves = append(theoreticalMoves, *upperLeft)
		}
	}

	return theoreticalMoves
}

func (p Pawn) filterBlockedSquares(board Board, fromSquare types.Coordinate, squaresToBeFiltered []types.Coordinate) []types.Coordinate {
	var nonBlockedSquares []types.Coordinate
	//order of movesToBeFiltered is important here
	for _, square := range squaresToBeFiltered {
		pieceAtSquare := board.getPieceAt(square)
		if square.Col == fromSquare.Col { // squares ahead
			if pieceAtSquare == nil {
				nonBlockedSquares = append(nonBlockedSquares, square)
			}
		} else { //squares that pawn attacks
			if pieceAtSquare != nil && pieceAtSquare.GetColor() != p.Color {
				nonBlockedSquares = append(nonBlockedSquares, square)
			}
		}
	}
	return lo.Intersect(nonBlockedSquares, squaresToBeFiltered)
}