using System;
using System.Linq;

namespace AirTrafficControl;

public enum AirTrafficRequest
{
   LandingRequest,
   TakeoffRequest,
   RunwayCrossingRequest,
   LandingRequestDone,
   TakeoffRequestDone,
   RunwayCrossingRequestDone,
}

public interface IColleague
{
   void ReceiveMessage(string instruction, bool accepted);
}

public interface IMediator
{
   void Notify(IColleague sender, AirTrafficRequest request);
}

public class Flight : IColleague
{
   private readonly IMediator _mediator;
   public string FlightNumber { get; }

   public Flight(string flightNumber, IMediator mediator)
   {
      FlightNumber = flightNumber;
      _mediator = mediator;
   }

   public void RequestLanding()
   {
      Console.WriteLine($"Flight {FlightNumber} requesting landing.");
      _mediator.Notify(this, AirTrafficRequest.LandingRequest);
   }

   public void RequestTakeoff()
   {
      Console.WriteLine($"Flight {FlightNumber} requesting takeoff.");
      _mediator.Notify(this, AirTrafficRequest.TakeoffRequest);
   }

   public void LandingCompleted()
   {
      Console.WriteLine($"Flight {FlightNumber} has completed landing.");
      _mediator.Notify(this, AirTrafficRequest.LandingRequestDone);
   }

   public void TakeoffCompleted()
   {
      Console.WriteLine($"Flight {FlightNumber} has completed takeoff.");
      _mediator.Notify(this, AirTrafficRequest.TakeoffRequestDone);
   }

   public void ReceiveMessage(string instruction, bool accepted)
   {
      if (accepted)
      {
         Console.WriteLine(
            $"Flight {FlightNumber} received instruction: {instruction}"
         );
      }
      else
      {
         Console.WriteLine(
            $"Flight {FlightNumber} received rejection for instruction: {instruction}"
         );
      }
   }
}

public class GroundVehicle : IColleague
{
   private readonly IMediator _mediator;
   public string VehicleId { get; }

   public GroundVehicle(string vehicleId, IMediator mediator)
   {
      VehicleId = vehicleId;
      _mediator = mediator;
   }

   public void RequestRunwayCrossing()
   {
      Console.WriteLine(
         $"Ground vehicle {VehicleId} requesting runway crossing."
      );
      _mediator.Notify(this, AirTrafficRequest.RunwayCrossingRequest);
   }

   public void RunwayCrossingCompleted()
   {
      Console.WriteLine(
         $"Ground vehicle {VehicleId} has completed runway crossing."
      );
      _mediator.Notify(this, AirTrafficRequest.RunwayCrossingRequestDone);
   }

   public void ReceiveMessage(string instruction, bool accepted)
   {
      if (accepted)
      {
         Console.WriteLine(
            $"Ground vehicle {VehicleId} received instruction: {instruction}"
         );
      }
      else
      {
         Console.WriteLine(
            $"Ground vehicle {VehicleId} received rejection for instruction: {instruction}"
         );
      }
   }
}

public class AirTrafficControlTower : IMediator
{
   private class Runway
   {
      public string Name { get; init; } = "";
      public IColleague? OccupiedBy { get; set; }

      public Runway(string name)
      {
         Name = name;
      }
   }

   private readonly Runway[] _runways = new Runway[30];

   public AirTrafficControlTower()
   {
      // create runways
      for (int i = 0; i < _runways.Length; i++)
      {
         _runways[i] = new Runway($"Runway R{i + 1}");
      }
   }

   public void Notify(IColleague sender, AirTrafficRequest request)
   {
      switch (request)
      {
         case AirTrafficRequest.LandingRequest:
            HandleLandingRequest(sender);
            break;
         case AirTrafficRequest.TakeoffRequest:
            HandleTakeoffRequest(sender);
            break;
         case AirTrafficRequest.RunwayCrossingRequest:
            HandleRunwayCrossingRequest(sender);
            break;
         case AirTrafficRequest.LandingRequestDone:
            HandleLandingRequestDone(sender);
            break;
         case AirTrafficRequest.TakeoffRequestDone:
            HandleTakeoffRequestDone(sender);
            break;
         case AirTrafficRequest.RunwayCrossingRequestDone:
            HandleRunwayCrossingRequestDone(sender);
            break;
         default:
            break;
      }
   }

   void HandleLandingRequest(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy is null);
      if (val is not null)
      {
         val.OccupiedBy = sender;
         sender.ReceiveMessage(
            $"Landing approved on {val.Name}.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "No available runways for landing.",
            accepted: false
         );
      }
   }

   void HandleTakeoffRequest(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy is null);
      if (val is not null)
      {
         val.OccupiedBy = sender;
         sender.ReceiveMessage(
            $"Takeoff approved on {val.Name}.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "No available runways for takeoff.",
            accepted: false
         );
      }
   }

   void HandleLandingRequestDone(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy == sender);
      if (val is not null)
      {
         val.OccupiedBy = null;
         sender.ReceiveMessage(
            $"You have cleared {val.Name} after landing.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "You were not occupying any runway.",
            accepted: false
         );
      }
   }

   void HandleTakeoffRequestDone(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy == sender);
      if (val is not null)
      {
         val.OccupiedBy = null;
         sender.ReceiveMessage(
            $"You have cleared {val.Name} after takeoff.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "You were not occupying any runway.",
            accepted: false
         );
      }
   }

   void HandleRunwayCrossingRequestDone(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy == sender);

      if (val is not null)
      {
         val.OccupiedBy = null;
         sender.ReceiveMessage(
            $"You have cleared {val.Name} after crossing.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "You were not occupying any runway.",
            accepted: false
         );
      }
   }

   void HandleRunwayCrossingRequest(IColleague sender)
   {
      Runway? val = _runways.FirstOrDefault(r => r.OccupiedBy is null);

      if (val is not null)
      {
         val.OccupiedBy = sender;
         sender.ReceiveMessage(
            $"Crossing approved on {val.Name}.",
            accepted: true
         );
      }
      else
      {
         sender.ReceiveMessage(
            "No available runways for crossing.",
            accepted: false
         );
      }
   }
}

internal class Program
{
   public static void Main()
   {
      var tower = new AirTrafficControlTower();

      Flight[] flights = new Flight[1000];

      for (int i = 0; i < flights.Length; i++)
      {
         flights[i] = new Flight($"F{i + 1:D4}", tower);
      }

      GroundVehicle[] vehicles = new GroundVehicle[10];

      for (int i = 0; i < vehicles.Length; i++)
      {
         vehicles[i] = new GroundVehicle($"V{i + 1:D3}", tower);
      }

      // create simulation with random events
      Random rand = new Random();

      ulong tick = 0;

      while (tick < 100_000) 
      {
         tick++;

         // randomly select a flight or vehicle to make a request
         int index = rand.Next(0, flights.Length + vehicles.Length);
         if (index < flights.Length)
         {
            Flight flight = flights[index];
            int action = rand.Next(0, 4);
            switch (action)
            {
               case 0:
                  flight.RequestLanding();
                  break;
               case 1:
                  flight.RequestTakeoff();
                  break;
               case 2:
                  flight.LandingCompleted();
                  break;
               case 3:
                  flight.TakeoffCompleted();
                  break;
            }
         }
         else
         {
            GroundVehicle vehicle = vehicles[index - flights.Length];
            int action = rand.Next(0, 2);
            switch (action)
            {
               case 0:
                  vehicle.RequestRunwayCrossing();
                  break;
               case 1:
                  vehicle.RunwayCrossingCompleted();
                  break;
            }
         }
      }
   }
}