var cellWidth = 0;
var gameOver = false;
var humanFirst;
var usePruning;
var gameBoard = [
['', '', ''],
['', '', ''],
['', '', '']
];
var currentPlayer = 0;
var players = ['X', 'O'];
var scores = {
	X: 1,
	Tie: 0,
	O: -1
};
var eh = true;

function setup() {
	var canvas = createCanvas(500, 500);
	cellWidth = floor(width / 3);
	canvas.parent('sketch-holder');
	humanFirst = document.getElementById("humanFirst").checked;
	usePruning = document.getElementById("usePruning").checked;
}

function draw() {
	background(220);

	strokeWeight(4);
	line(0, height / 3, width, height / 3);
	line(0, height - height / 3, width, height - height / 3);
	line(width / 3, 0, width / 3, height);
	line(width - width / 3, 0, width - width / 3, height);

	if(!humanFirst) nextTurn();
	
	noLoop();
}

function nextTurn() { //minimax
	let bestScore = players[currentPlayer] == 'X' ? -Infinity : Infinity;
	let move;
	
	for(let i = 0; i < 3; i++)
		for(let j = 0; j < 3; j++) {
			if(gameBoard[i][j] == ''){
				gameBoard[i][j] = players[currentPlayer];
				let score;
				
				if(!usePruning) score = minimax(gameBoard, !(players[currentPlayer] == 'X'));
				else score = minimaxPrune(gameBoard, -Infinity, Infinity, !(players[currentPlayer] == 'X'));
				gameBoard[i][j] = '';
				
				if(players[currentPlayer] == 'X') {
					if(score > bestScore){
						bestScore = score;
						
						move = {i, j};
					}
				}
				else {
					if(score < bestScore){
						bestScore = score;
						
						move = {i, j};
					}
				}
			}
		}
		
	gameBoard[move.i][move.j] = players[currentPlayer];
	drawPlayer(move.j, move.i, cellWidth, players[currentPlayer]);
	currentPlayer = (currentPlayer + 1) % players.length;
}

function minimaxPrune(board, alpha, beta, isMaximizing){
	let result = checkWinner(board);
	
	if(result != null) {
		return scores[result];
	}
	
	if(isMaximizing){
		let bestScore = -Infinity;
		
		for(let i = 0; i < 3; i++)
			for(let j = 0; j < 3; j++) {
				if(board[i][j] == ''){
					board[i][j] = 'X';
					let score = minimaxPrune(board, alpha, beta, false);
					board[i][j] = '';
					bestScore = max(score, bestScore);
					alpha = max(alpha, bestScore);
					
					if(beta <= alpha)
						return bestScore;
				}
			}
		return bestScore;
	}
	else {
		let bestScore = Infinity;
		
		for(let i = 0; i < 3; i++)
			for(let j = 0; j < 3; j++) {
				if(board[i][j] == ''){
					board[i][j] = 'O';
					let score = minimaxPrune(board, alpha, beta, true);
					board[i][j] = '';
					if (score > 1 || score < -1) print(score);
					bestScore = min(score, bestScore);
					beta = min(beta, bestScore);
					
					if(beta <= alpha)
						return bestScore;
				}
			}		
		return bestScore;
	}	
}

function minimax(board, isMaximizing){
	let result = checkWinner(board);
	
	if(result != null) {
		return scores[result];
	}
	
	if(isMaximizing){
		let bestScore = -Infinity;
		
		for(let i = 0; i < 3; i++)
			for(let j = 0; j < 3; j++) {
				if(board[i][j] == ''){
					board[i][j] = 'X';
					let score = minimax(board, false);
					board[i][j] = '';
					
					bestScore = max(score, bestScore);
				}
			}
		return bestScore;
	}
	else {
		let bestScore = Infinity;
		
		for(let i = 0; i < 3; i++)
			for(let j = 0; j < 3; j++) {
				if(board[i][j] == ''){
					board[i][j] = 'O';
					let score = minimax(board, true);
					board[i][j] = '';
					
					bestScore = min(score, bestScore);
				}
			}		
		return bestScore;
	}
}

function checkWinner(board, showEnd = false){
	let winner = null;
	// Horizontal
	for(let i = 0; i < 3; i++){
		if(board[i][0] == board[i][1] && board[i][1] == board[i][2] && board[i][0] != ''){
			winner = board[i][0];
			let y = 0;
			
			if(i == 0) y = cellWidth / 2;
			else y = cellWidth * i + cellWidth / 2;
			
			if(showEnd) line(0, y, width, y);
		}
	}
	
	// Vertical
	for(let i = 0; i < 3; i++){
		if(board[0][i] == board[1][i] && board[1][i] == board[2][i] && board[0][i] != ''){
			winner = board[0][i];
			let x = 0;
			
			if(i == 0) x = cellWidth / 2;
			else x = cellWidth * i + cellWidth / 2;
			
			if(showEnd) line(x, 0, x, width);
		}
	}
	// Diagonal
	if(board[0][0] != '' && board[0][0] == board[1][1] && board[2][2] == board[0][0]){
		winner = board[0][0];
		if(showEnd) line(0, 0, width, width);
	}
	else if(board[2][0] != '' && board[2][0] == board[1][1] && board[0][2] == board[2][0]){
		winner = board[2][0];
		if(showEnd) line(width, 0, 0, width);
	}
	
	let openMoves = 0;
	
	for(let i = 0; i < 3; i++)
		for(let j = 0; j < 3; j++)
			if(board[i][j] == '')
				openMoves++;
	
	if(!winner && openMoves == 0)
		return "Tie";
	
	return winner;
}

function mouseClicked(){
	if(gameOver) {
		return;
	}
	
	let x = floor(mouseX / cellWidth);
	let y = floor(mouseY / cellWidth);
	
	if(gameBoard[y][x] == ''){
		drawPlayer(x, y, cellWidth, players[currentPlayer]);
		gameBoard[y][x] = players[currentPlayer];

		let result = checkWinner(gameBoard, true);
		
		if(result != null) {
			showWinner(result);
			return;
		}

		currentPlayer = (currentPlayer + 1) % players.length;

		nextTurn();
		
		result = checkWinner(gameBoard, true);
		
		if(result != null)
			showWinner(result);
	}
}

function showWinner(player) {
	gameOver = true;
	
	if(player == "Tie")
		document.getElementById("statusLabel").innerHTML = `<h1>Its a tie. (Pruning? ${usePruning})</h1>`;
	else
		document.getElementById("statusLabel").innerHTML = `<h1>Game over ${player} wins! (Pruning? ${usePruning})</h1>`;
}

function drawPlayer(x, y, w, player) {
	strokeWeight(2);
	
	if(player == 'O'){
		fill(220);
		ellipse(w / 2 + w * x, w / 2 + w * y, floor(width / 4));
	}
	else if (player == 'X'){
		let newX = w * x;
		let newY = w * y;
		let trim = w * 0.90;
		line(newX + trim * 0.15, newY + trim * 0.15, newX + trim, newY + trim);
		line(newX + trim * 0.15, newY + trim, newX + trim, newY + trim * 0.15);
	}
	
	strokeWeight(10);
}