TicTacToe/Game.cs

namespace TicTacToe
{
    public class Game
    {
        Form1 form;
        Box[] boxes = new Box[9];
        bool BotRound = false;

        public Game()
        {
            form = Program.form;
            boxes[0] = new Box(form.grid_0, 0); boxes[0].Pressed += ButtonClicked;
            boxes[1] = new Box(form.grid_1, 1); boxes[1].Pressed += ButtonClicked;
            boxes[2] = new Box(form.grid_2, 2); boxes[2].Pressed += ButtonClicked;
            boxes[3] = new Box(form.grid_3, 3); boxes[3].Pressed += ButtonClicked;
            boxes[4] = new Box(form.grid_4, 4); boxes[4].Pressed += ButtonClicked;
            boxes[5] = new Box(form.grid_5, 5); boxes[5].Pressed += ButtonClicked;
            boxes[6] = new Box(form.grid_6, 6); boxes[6].Pressed += ButtonClicked;
            boxes[7] = new Box(form.grid_7, 7); boxes[7].Pressed += ButtonClicked;
            boxes[8] = new Box(form.grid_8, 8); boxes[8].Pressed += ButtonClicked;
        }

        public void Start()
        {
            Round();
        }

        public void ButtonClicked(int index)
        {
            Box box = boxes[index];
            if (box.Filled) return;
            box.PlayerClaim(BotRound);
            RoundEnded();
        }

        public void Round()
        {
            if (BotRound)
            {
                BotTurn();
            }
            else
            {
                PlayerTurn();
            }
        }

        public void BotTurn()
        {
            SetInputEnabled(false);

            Random random = new Random();

            var empty = boxes.Where(b => !b.Filled).ToList();

            // try to win
            foreach (Box b in empty)
            {
                b.BotOwned = true;
                b.Filled = true;

                if (CheckWins(true))
                {
                    b.PlayerClaim(true);
                    RoundEnded();
                    return;
                }

                b.BotOwned = false;
                b.Filled = false;
            }

            // try to block
            foreach (Box b in empty)
            {
                b.BotOwned = false;
                b.Filled = true;

                if (CheckWins(false))
                {
                    b.PlayerClaim(true);
                    RoundEnded();
                    return;
                }

                b.Filled = false;
            }

            // pick middle
            if (!boxes[4].Filled)
            {
                boxes[4].PlayerClaim(true);
                RoundEnded();
                return;
            }

            // else pick random
            int index = random.Next(0, empty.Count);
            Box box = empty[index];
            box.PlayerClaim(true);

            RoundEnded();
        }

        public bool CheckWins(bool bot) // check if bot won, or player if bot == true
        {
            int[][] lines =
            {
                [0, 1, 2],
                [3, 4, 5],
                [6, 7, 8],
                [0, 3, 6],
                [1, 4, 7],
                [2, 5, 8],
                [0, 4, 8],
                [2, 4, 6]
            };

            foreach (var line in lines)
            {
                if (!boxes[line[0]].Filled || !boxes[line[1]].Filled || !boxes[line[2]].Filled)
                    continue;

                if (boxes[line[0]].BotOwned == bot &&
                    boxes[line[1]].BotOwned == bot &&
                    boxes[line[2]].BotOwned == bot)
                {
                    return true;
                }
            }

            return false;
        }

        public void PlayerTurn()
        {
            SetInputEnabled(true);
        }

        public void RoundEnded()
        {
            if (CheckWins(BotRound))
            {
                if (BotRound)
                {
                    MessageBox.Show("You lost");
                    Program.AddLose();
                }
                else
                {
                    MessageBox.Show("You won");
                    Program.AddWin();
                }
                return;
            }

            BotRound = !BotRound;

            if (IsAllBoxesFilled())
            {
                MessageBox.Show("Tie");
            }
            else
            {
                Round();
            }
        }

        public bool IsAllBoxesFilled()
        {
            foreach (Box box in boxes)
            {
                if (!box.Filled)
                    return false;
            }

            return true;
        }

        public void SetInputEnabled(bool value)
        {
            foreach (Box box in boxes)
            {
                box.SetEnabled(value);
            }
        }

        public void Destroy()
        {
            foreach (Box box in boxes)
            {
                box.Destroy();
            }
        }
    }
}