class FlightBookingSystem {
    constructor(agencyName) {
        this.agencyName = agencyName;
        this.flights = [];
        this.bookings = [];
        this.bookingsCount = 0;
    }

    addFlight(flightNumber, destination, departureTime, price) {
        const flightExists = this.flights.some(
            (flight) => flight.flightNumber === flightNumber
        );
        if (flightExists) {
            return `Flight ${flightNumber} to ${destination} is already available.`;
        }
        this.flights.push({
            flightNumber,
            destination,
            departureTime,
            price,
        });
        return `Flight ${flightNumber} to ${destination} has been added to the system.`;
    }

    bookFlight(passengerName, flightNumber) {
        const flight = this.flights.find(
            (flight) => flight.flightNumber === flightNumber
        );
        if (!flight) {
            return `Flight ${flightNumber} is not available for booking.`;
        }
        this.bookings.push({
            passengerName,
            flightNumber,
        });
        this.bookingsCount++;
        return `Booking for passenger ${passengerName} on flight ${flightNumber} is confirmed.`;
    }

    cancelBooking(passengerName, flightNumber) {
        const bookingIndex = this.bookings.findIndex(
            (booking) =>
                booking.passengerName === passengerName &&
                booking.flightNumber === flightNumber
        );
        if (bookingIndex === -1) {
            throw new Error(
                `Booking for passenger ${passengerName} on flight ${flightNumber} not found.`
            );
        }
        this.bookings.splice(bookingIndex, 1);
        this.bookingsCount--;
        return `Booking for passenger ${passengerName} on flight ${flightNumber} is cancelled.`;
    }

    showBookings(criteria) {
        if (this.bookings.length === 0) {
            throw new Error(`No bookings have been made yet.`);
        }
        if (criteria === "all") {
            let bookingsList = `All bookings(${this.bookingsCount}):\n`;
            this.bookings.forEach((booking) => {
                bookingsList += `${booking.passengerName} booked for flight ${booking.flightNumber}.\n`;
            });
            return bookingsList.trim();
        } else if (criteria === "cheap") {
            const cheapBookings = this.bookings.filter(
                (booking) =>
                    this.flights.find((flight) => flight.flightNumber === booking.flightNumber).price <= 100
            );
            if (cheapBookings.length === 0) {
                return "No cheap bookings found.";
            }
            let bookingsList = "Cheap bookings:\n";
            cheapBookings.forEach((booking) => {
                bookingsList += `${booking.passengerName} booked for flight ${booking.flightNumber}.\n`;
            });
            return bookingsList.trim();
        } else if (criteria === "expensive") {
            const expensiveBookings = this.bookings.filter(
                (booking) =>
                    this.flights.find((flight) => flight.flightNumber === booking.flightNumber).price > 100
            );
            if (expensiveBookings.length === 0) {
                return "No expensive bookings found.";
            }
            let bookingsList = "Expensive bookings:\n";
            expensiveBookings.forEach((booking) => {
                bookingsList += `${booking.passengerName} booked for flight ${booking.flightNumber}.\n`;
            });
            return bookingsList.trim();
        } else {
            throw new Error(`Invalid criteria: ${criteria}`);
        }
    }
}