using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        WeatherDataHandler weatherData = new WeatherDataHandler();

        CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);

        HeatIndexDisplay heatIndexDisplay = new HeatIndexDisplay(weatherData);      

        weatherData.SetMeasurements(80, 65, 30.4f);

        weatherData.SetMeasurements(82, 70, 29.2f);

        weatherData.SetMeasurements(78, 90, 29.2f);

    }

}

​

​

public interface IDisplayElement {

    void display();

}

​

public class WeatherDataHandler : IObservable<WeatherDataInfo> {

    private List<IObserver<WeatherDataInfo>> observers;

    private List<WeatherDataInfo> weatherData;

    public WeatherDataHandler()

    {

        observers = new List<IObserver<WeatherDataInfo>>();

        weatherData = new List<WeatherDataInfo>();

    }

    public IDisposable Subscribe(IObserver<WeatherDataInfo> observer)

    {

         // Check whether observer is already registered. If not, add it

          if (! observers.Contains(observer)) {

             observers.Add(observer);

             // Provide observer with existing data.

             foreach (var item in weatherData)

                observer.OnNext(item);

          }

          return new Unsubscriber<WeatherDataInfo>(observers, observer);

    }

    public void SetMeasurements(float temperature, float humidity, float pressure)

    {

        var info = new WeatherDataInfo(temperature, humidity, pressure);

        weatherData.Add(info);

         foreach (var observer in observers)

            observer.OnNext(info);

    }

​

}

​

internal class Unsubscriber<WeatherDataInfo> : IDisposable

{

   private List<IObserver<WeatherDataInfo>> _observers;

   private IObserver<WeatherDataInfo> _observer;

​

   internal Unsubscriber(List<IObserver<WeatherDataInfo>> observers, IObserver<WeatherDataInfo> observer)

   {

      this._observers = observers;

      this._observer = observer;

   }

​

   public void Dispose() 

   {

      if (_observers.Contains(_observer))

         _observers.Remove(_observer);

   }

}

​

public class WeatherDataInfo {

    private float temperature;

    private float humidity;

    private float pressure;

​

    public float Temperature { get {return temperature;} }

    public float Humidity { get {return humidity;} }

    public float Pressure { get {return pressure;} }

    public WeatherDataInfo(float temperature, float humidity, float pressure)

    {

        this.temperature = temperature;

        this.humidity = humidity;

        this.pressure = pressure;

    }

}

​

public class CurrentConditionsDisplay : IDisplayElement, IObserver<WeatherDataInfo>

{

    private float temperature;

    private float humidity;

    private IDisposable cancellation;

    public CurrentConditionsDisplay(WeatherDataHandler provider)

    {

        cancellation = provider.Subscribe(this);

    }

    public virtual void OnNext(WeatherDataInfo value)

    {

        this.temperature = value.Temperature;

        this.humidity = value.Humidity;

        display();

    }

    public virtual void OnError(Exception e)

    {}

​

    public virtual void OnCompleted()

    {

      this.Unsubscribe();

    }

    public virtual void Unsubscribe()

    {

        cancellation.Dispose();

    }

​

    public void display() {

        Console.WriteLine("Current conditions: " + temperature + "F degrees and " + humidity + "% humidity");

    }

}

​

public class HeatIndexDisplay : IDisplayElement, IObserver<WeatherDataInfo>

{

    private float temperature;

    private float humidity;

    private float heatIndex;

    private IDisposable cancellation;

    public virtual void OnError(Exception e)

    {}

    public virtual void OnCompleted()

    {

      this.Unsubscribe();

    }

    public virtual void Unsubscribe()

    {

        cancellation.Dispose();

    }

    public HeatIndexDisplay(WeatherDataHandler provider)

    {

        cancellation = provider.Subscribe(this); 

    }

    public virtual void OnNext(WeatherDataInfo value)

    {

        this.temperature = value.Temperature;

        this.humidity = value.Humidity;

        this.heatIndex = computeHeatIndex(temperature, humidity);

        display();

    }

    private float computeHeatIndex(float t, float rh) {

        float index = (float)((16.923 + (0.185212 * t) + (5.37941 * rh) - (0.100254 * t * rh) +

            (0.00941695 * (t * t)) + (0.00728898 * (rh * rh)) +

            (0.000345372 * (t * t * rh)) - (0.000814971 * (t * rh * rh)) +

            (0.0000102102 * (t * t * rh * rh)) - (0.000038646 * (t * t * t)) + (0.0000291583 *  

            (rh * rh * rh)) + (0.00000142721 * (t * t * t * rh)) +

            (0.000000197483 * (t * rh * rh * rh)) - (0.0000000218429 * (t * t * t * rh * rh)) +     

            0.000000000843296 * (t * t * rh * rh * rh)) -

            (0.0000000000481975 * (t * t * t * rh * rh * rh)));

        return index;

    }

    public void display() {

        Console.WriteLine("Heat index is " + heatIndex);

    }

}