class Parking {

    constructor(capacity) {
        this.capacity = capacity;
        this.vehicles = [];
    }

    addCar(carModel, carNumber) {

        if (this.capacity <= this.vehicles.length) {
            throw new Error('Not enough parking space.');
        }

        let car = {
            carModel: carModel,
            carNumber: carNumber,
            payed: false
        };

        this.vehicles.push(car);
        return `The ${carModel}, with a registration number ${carNumber}, parked.`;
    }

    removeCar(carNumber) {

        if (this.vehicles.some(car => car.carNumber === carNumber)) {

            let car = this.vehicles.find(car => car.carNumber === carNumber);
            let index = this.vehicles.indexOf(car);

            if (car.payed === false) {
                throw new Error(`${carNumber} needs to pay before leaving the parking lot.`);
            } else {
                this.vehicles.splice(index, 1);
                return `${carNumber} left the parking lot.`;
            }

        } else {
            throw new Error('The car, you\'re looking for, is not found.');
        }
    }

    pay(carNumber) {

        if (this.vehicles.some(car => car.carNumber === carNumber)) {

            let car = this.vehicles.find(car => car.carNumber === carNumber);

            if (car.payed === false) {
                car.payed = true;
                return `${carNumber}\'s driver successfully payed for his stay.`;

            } else {
                throw new Error(`${carNumber}\'s driver has already payed his ticket.`);
            }

        } else {
            throw new Error(`${carNumber} is not in the parking lot.`);
        }
    }

    getStatistics(carNumber) {

        if (this.vehicles.some(car => car.carNumber === carNumber)) {

            let car = this.vehicles.find(car => car.carNumber === carNumber);

            let stringFlag = car.payed === false
                    ? 'Not payed'
                    : 'Has payed';

            return `${car.carModel} == ${car.carNumber} - ${stringFlag}`;

        } else {

            let emptySlots = this.capacity - this.vehicles.length;
            let result = [`The Parking Lot has ${emptySlots} empty spots left.`];

            this.vehicles.sort((a, b) => a.carModel.localeCompare(b.carModel)).forEach(car => {

                let stringFlag = car.payed === false
                    ? 'Not payed'
                    : 'Has payed';

                result.push(`${car.carModel} == ${car.carNumber} - ${stringFlag}`);
            });

            return result.join('\n');
        }
    }
}