connect-four/src/Game.js

Lightweight connect-four game logic

'use strict';

var Emitter = require('events');
var checkWin = require('./checkWin');

function Game (settings) {
	settings = settings || {};
	this._events = {};
	this.rows = settings.rows || 6;
	this.cols = settings.cols || 7;
	this.board = settings.board || {};

	this.cells = this.rows * this.cols;

	this.on('play', checkWin);
}

var API = Game.prototype = new Emitter();
API.setMaxListeners(Infinity);

API.constructor = Game;
API.ended = false;
API.winner = null;

API.format = function (col, row) {
	return col + ':' + row;
};

API.get = function (col, row) {
	var prop = this.format(col, row);
	var has = this.board.hasOwnProperty(prop);

	return has ? this.board[prop] : null;
};

API.played = function (col) {
	var prop, index = 0;
	while (index < this.rows) {
		prop = this.format(col, index);
		if (!this.board.hasOwnProperty(prop)) {
			return index;
		}
		index += 1;
	}

	return this.rows;
};

API.validMove = function (col) {
	var inBounds = col >= 0 && col < this.cols;
	var hasSpace = this.played(col) < this.rows;

	return inBounds && hasSpace;
};

API.play = function (player, col) {
	if (this.ended) {
		return this;
	}
	var index = this.played(col);

	if (!this.validMove(col)) {
		throw new Error(
			'Move falls out of the game: ' +
			'column #' + col + '.' +
			'\nUse ".validMove(column)" to check validity ' +
			'before calling ".play()".'
		);
	}
	this.board[this.format(col, index)] = player;
	this.emit('play', player, {
		col: col,
		row: index
	}, this);

	if ((this.cells -= 1) <= 0) {
		this.end();
	}

	return this;
};

API.end = function (player) {
	if (this.ended) {
		return this;
	}
	this.ended = true;
	this.winner = player || null;
	this.emit('end', player, this);

	return this;
};

API.toJSON = function () {
	return {
		cols: this.cols,
		rows: this.rows,
		board: this.board
	};
};

module.exports = Game;