Author a game with core directly

import { defineEvent, defineGame } from "@openturn/core";

export const game = defineGame({
  maxPlayers: 2,
  events: {
    place_mark: defineEvent<{ row: number; col: number }>(),
  },
  initial: "play",
  setup: () => ({ board: createEmptyBoard() }),
  selectors: {
    winnerMark: ({ G }) => getWinner(G.board),
  },
  states: {
    play: {
      activePlayers: ({ match, position }) =>
        [match.players[(position.turn - 1) % match.players.length]!],
      label: "Take your turn",
      control: () => ({ status: "playing" }),
    },
    won: {
      activePlayers: () => [],
      label: "Winner",
      control: () => ({ status: "won" }),
    },
  },
  transitions: ({ transition }) => [
    transition("place_mark", {
      from: "play",
      to: "won",
      turn: "increment",
      label: "place_mark:win",
      resolve: ({ G, event, playerID }) => {
        const board = placeMark(G.board, event.payload.row, event.payload.col, playerID);
        if (board === null || getWinner(board) === null) return null;
        return { G: { board }, result: { winner: playerID } };
      },
    }),
    // more branches: draw, continue...
  ],
  views: {
    public: ({ G }) => ({ board: G.board }),
  },
});

events: {
  place_mark: defineEvent<{ row: number; col: number }>(),
  concede: defineEvent(),
},

states: {
  play: {
    activePlayers: ({ match, position }) => [currentPlayerID(match, position)],
    label: ({ match, position }) => `Player ${currentPlayerID(match, position)}`,
    control: () => ({ status: "playing" }),
    metadata: ({ G }) => [{ key: "moves_made", value: countMoves(G) }],
  },
},
initial: "play",

transitions: ({ transition }) => [
  transition("place_mark", {
    from: "play",
    to: "play",
    label: "place_mark:continue",
    turn: "increment",
    resolve: ({ G, event, playerID }) => {
      const board = placeMark(G.board, event.payload.row, event.payload.col, playerID);
      if (board === null || getWinner(board) !== null) return null;
      return { G: { board } };
    },
  }),
],

selectors: {
  isBoardFull: ({ G }) => G.board.every((row) => row.every((cell) => cell !== null)),
},
views: {
  public: ({ G }) => ({ board: G.board }),
  player: ({ G, match }, playerID) => ({ board: G.board, myID: playerID }),
},