How to Build a Chess App in SwiftUI

import SwiftData
import Foundation

enum PieceType: String, Codable {
    case king, queen, rook, bishop, knight, pawn
}
enum PieceColor: String, Codable { case white, black }

struct ChessPiece: Codable, Identifiable {
    var id       = UUID()
    var type:    PieceType
    var color:   PieceColor
    var file:    Int        // 0 (a-file) – 7 (h-file)
    var rank:    Int        // 0 – 7
    var hasMoved = false

    var symbol: String {
        let w = [PieceType.king:"♔",.queen:"♕",.rook:"♖",
                 .bishop:"♗",.knight:"♘",.pawn:"♙"]
        let b = [PieceType.king:"♚",.queen:"♛",.rook:"♜",
                 .bishop:"♝",.knight:"♞",.pawn:"♟"]
        return (color == .white ? w : b)[type] ?? "?"
    }
}

@Model final class ChessGame {
    var id          = UUID()
    var boardData   = Data()        // JSON-encoded [ChessPiece]
    var currentTurn = "white"
    var moveHistory = [String]()    // algebraic notation
    var status      = "active"      // active | checkmate | stalemate | draw
    var createdAt   = Date()
}

struct ChessBoardView: View {
    @ObservedObject var vm: ChessGameViewModel

    var body: some View {
        VStack(spacing: 0) {
            ForEach((0..<8).reversed(), id: \.self) { rank in
                HStack(spacing: 0) {
                    ForEach(0..<8, id: \.self) { file in
                        SquareView(
                            file: file, rank: rank,
                            piece: vm.piece(at: file, rank: rank),
                            isSelected:  vm.selectedSquare == [file, rank],
                            isValidMove: vm.validMoves.contains([file, rank])
                        )
                        .onTapGesture { vm.handleTap(file: file, rank: rank) }
                    }
                }
            }
        }
        .aspectRatio(1, contentMode: .fit)
        .clipShape(RoundedRectangle(cornerRadius: 6))
        .shadow(radius: 8)
    }
}

struct SquareView: View {
    let file, rank: Int;  let piece: ChessPiece?
    let isSelected, isValidMove: Bool

    var bg: Color { (file + rank) % 2 == 0
        ? Color(red: 0.71, green: 0.53, blue: 0.39)
        : Color(red: 0.94, green: 0.85, blue: 0.71) }

    var body: some View {
        ZStack {
            bg
            if isSelected  { Color.yellow.opacity(0.4) }
            if isValidMove { Circle().fill(Color.black.opacity(0.18)).padding(12) }
            if let p = piece { Text(p.symbol).font(.system(size: 38)) }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}

actor ChessAI {
    func bestMove(board: ChessBoard, depth: Int = 3) async -> Move? {
        var best: Move?
        var bestScore = Int.min
        for move in board.legalMoves(for: .black) {
            let score = minimax(board.applying(move), depth: depth - 1,
                                alpha: Int.min, beta: Int.max,
                                maximizing: false)
            if score > bestScore { bestScore = score; best = move }
        }
        return best
    }

    private func minimax(_ board: ChessBoard, depth: Int,
                         alpha: Int, beta: Int,
                         maximizing: Bool) -> Int {
        guard depth > 0, board.status == .active else { return board.evaluate() }
        var α = alpha, β = beta
        let color: PieceColor = maximizing ? .black : .white
        var value = maximizing ? Int.min : Int.max
        for move in board.legalMoves(for: color) {
            let s = minimax(board.applying(move), depth: depth - 1,
                            alpha: α, beta: β, maximizing: !maximizing)
            if maximizing { value = max(value, s); α = max(α, value) }
            else          { value = min(value, s); β = min(β, value) }
            if α >= β { break }   // α-β cut-off
        }
        return value
    }
}

// In your ViewModel, after the player's move:
Task {
    if let move = await ai.bestMove(board: currentBoard) {
        await MainActor.run { applyMove(move) }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
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