using System;
using System.Collections.Generic;

namespace TicTacToe
{
    public class AIPlayer
    {
        private Game game;
        private Game.SquareState mySymbol;
        private Game.SquareState opponentSymbol;

        public AIPlayer(Game game, Game.SquareState mySymbol)
        {
            this.game = game;
            this.mySymbol = mySymbol;
            opponentSymbol = (mySymbol == Game.SquareState.X) ? Game.SquareState.O : Game.SquareState.X;
        }

        public (int, int) MakeMove()
        {
            (int, int) bestMove = (-1, -1);
            int bestScore = Int32.MinValue;
            foreach ((int x, int y) in game.GetAvailableMoves())
            {
                game.MakeMove(x, y, mySymbol);
                int score = Minimax(game, 0, false);
                game.MakeMove(x, y, Game.SquareState.Empty); // undo move
                if (score > bestScore)
                {
                    bestScore = score;
                    bestMove = (x, y);
                }
            }
            return bestMove;
        }

        private int Minimax(Game game, int depth, bool isMaximizing)
        {
            if (game.CheckForWinner())
            {
                return isMaximizing ? -1 : 1;
            }
            if (game.IsBoardFull())
            {
                return 0;
            }

            if (isMaximizing)
            {
                int maxScore = Int32.MinValue;
                foreach ((int x, int y) in game.GetAvailableMoves())
                {
                    game.MakeMove(x, y, mySymbol);
                    int score = Minimax(game, depth + 1, false);
                    game.MakeMove(x, y, Game.SquareState.Empty); // undo move
                    maxScore = Math.Max(maxScore, score);
                }
                return maxScore;
            }
            else
            {
                int minScore = Int32.MaxValue;
                foreach ((int x, int y) in game.GetAvailableMoves())
                {
                    game.MakeMove(x, y, opponentSymbol);
                    int score = Minimax(game, depth + 1, true);
                    game.MakeMove(x, y, Game.SquareState.Empty); // undo move
                    minScore = Math.Min(minScore, score);
                }
                return minScore;
            }
        }
    }
}