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

    addFlight(flightNumber, destination, departureTime, price) {
        if (this.flights.some(f => f.flightNumber === flightNumber)) {
            return `Flight ${flightNumber} to ${destination} is already available.`;
        } else {
            let flight = {
                flightNumber,
                destination,
                departureTime,
                price,
                bookings: 0
            };
            this.flights.push(flight);
            return `Flight ${flightNumber} to ${destination} has been added to the system.`;
        }
    }

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

    cancelBooking(passengerName, flightNumber) {
        const index = this.bookings.findIndex(b => b.passengerName === passengerName && b.flightNumber === flightNumber);
        if (index === -1) {
            throw new Error(`Booking for passenger ${passengerName} on flight ${flightNumber} not found.`);
        }
        this.bookings.splice(index, 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 result = `All bookings(${this.bookingsCount}):`;
            for (let i = 0; i < this.bookings.length; i++) {
                const booking = this.bookings[i];
                result += `\n${booking.passengerName} booked for flight ${booking.flightNumber}.`;
            }
            return result;
        } else if (criteria === "cheap") {
            let cheapBookings = this.bookings.filter(b => this.flights[b.flightNumber].price <= 100);
            if (cheapBookings.length === 0) {
                return "No cheap bookings found.";
            }
            let result = "Cheap bookings:";
            for (let i = 0; i < cheapBookings.length; i++) {
                let booking = cheapBookings[i];
                result += `\n${booking.passengerName} booked for flight ${booking.flightNumber}.`;
            }
            return result;
        } else if (criteria === "expensive") {
            let expensiveBookings = this.bookings.filter(b => this.flights[b.flightNumber].price > 100);
            if (expensiveBookings.length === 0) {
                return "No expensive bookings found.";
            }
            let result = "Expensive bookings:";
            for (let booking of expensiveBookings) {
                result += `\n${booking.passengerName} booked for flight ${booking.flightNumber}.`;
            }
            return result;
        } else {
            throw new Error(`Invalid criteria: ${criteria}`);
        }
    }
}