Railway.js

var Railway = Railway || {};

(function(Railway) {

    var Train = function(settings) {
        settings = settings || {};

        this.mainCoupeSize = settings.mainCoupeSize || 4;
        this.leftCoupeSize = settings.leftCoupeSize || 2;
        this.coupeCount = settings.coupeCount || 9;
        this.totalMainSeatsOffset = this.coupeCount * this.mainCoupeSize;
        this.seatToCoupes = {};

        this._calculateSeatMap();
    };

    Train.prototype._calculateSeatMap = function() {
        this.seatToCoupes = {};

        for (var currentCoupe = 1; currentCoupe <= this.coupeCount; currentCoupe++)
        {
            for (var offsetMainSeatNumber = 1; offsetMainSeatNumber <= this.mainCoupeSize; offsetMainSeatNumber++)
            {
                var currentMainSeatNumber = (currentCoupe - 1) * this.mainCoupeSize + offsetMainSeatNumber;
                this.seatToCoupes[currentMainSeatNumber] = currentCoupe;
            }

            for (var offsetLeftSeatNumber = 1; offsetLeftSeatNumber <= this.leftCoupeSize; offsetLeftSeatNumber++)
            {
                var currentLeftSeatNumber =
                    (this.coupeCount - currentCoupe) * this.leftCoupeSize +
                    offsetLeftSeatNumber +
                    this.totalMainSeatsOffset;

                this.seatToCoupes[currentLeftSeatNumber] = currentCoupe;
            }
        }
    };

    Train.prototype.getCoupeBySeat = function(seatNumber) {
        if (!this.seatToCoupes.hasOwnProperty(seatNumber)) {
            throw new Error("Invalid seat number");
        } else {
            return this.seatToCoupes[seatNumber];
        }
    };

    if (module) {
        module.exports = {
            Train: Train
        };
    } else {
        Railway = {
            Train: Train
        };
    }

})(Railway);