HeadFirstDesignPatterns/Ch2Weather/Weather.cs

namespace Ch2Weather;

public record struct WeatherRecord(double Temperature, double Humidity, double Pressure);

public interface IWeatherSubject {
    void Subscribe(IWeatherObserver o);
    void Unsubscribe(IWeatherObserver o);
    void NotifyObservers();
}

public interface IWeatherObserver {
    void Update(WeatherRecord wr);
}

public interface IWeatherDisplay {
    void Display();
}

public class WeatherData(WeatherRecord weatherRecord) : IWeatherSubject {
    private readonly List<IWeatherObserver> _observers = [];
    private WeatherRecord _weatherRecord = weatherRecord;

    public WeatherRecord WeatherRecord {
        get => _weatherRecord;
        set {
            _weatherRecord = value;
            NotifyObservers();
        }
    }

    public void Subscribe(IWeatherObserver o) {
        _observers.Add(o);
    }

    public void Unsubscribe(IWeatherObserver o) {
        _observers.Remove(o);
    }

    public void NotifyObservers() {
        foreach (var o in _observers) {
            o.Update(_weatherRecord);
        }
    }
}

public class CurrentConditionsDisplay : IWeatherObserver, IWeatherDisplay {
    private IWeatherSubject _subject;
    private double _temperature = 0;
    private double _humidity = 0;
    
    public CurrentConditionsDisplay(IWeatherSubject subject) {
        _subject = subject;
        subject.Subscribe(this);
    }

    public void Update(WeatherRecord wr) {
        _temperature = wr.Temperature;
        _humidity = wr.Humidity;
        Display();
    }

    public void Display() {
        Console.WriteLine($"Current conditions: {_temperature}C degrees and {_humidity}% humidity.");
    }
}

public class HeatIndexDisplay : IWeatherObserver, IWeatherDisplay {
    private IWeatherSubject _subject;
    private WeatherRecord _weatherRecord = new WeatherRecord(0,0,0);

    public HeatIndexDisplay(IWeatherSubject subject) {
        _subject = subject;
        subject.Subscribe(this);
    }
    
    private double ComputeHeatIndex(double t, double rh) {
        return (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));
    }  
    public void Update(WeatherRecord wr) {
        _weatherRecord = wr;
        Display();
    }

    public void Display() {
        var heatIndex = ComputeHeatIndex(_weatherRecord.Temperature, _weatherRecord.Humidity);
        Console.WriteLine($"Heat Index is {heatIndex}");
    }
}

public class TemperatureStatsDisplay : IWeatherObserver, IWeatherDisplay {
    private IWeatherSubject _subject;
    private double _n = 0;
    private double _avg = 0;
    private double _min = 0;
    private double _max = 0;

    public TemperatureStatsDisplay(IWeatherSubject subject) {
        _subject = subject;
        subject.Subscribe(this);
    }
    
    public void Update(WeatherRecord wr) {
        var temp = wr.Temperature;
        if (_n == 0) {
            _n = 1;
            _avg = temp;
            _min = temp;
            _max = temp;
        } else {
            _min = double.Min(_min, temp);
            _max = double.Max(_max, temp);
            _avg = (_avg * _n + temp) / (_n + 1);
            _n += 1;
        }
        Display();
    }

    public void Display() {
        Console.WriteLine($"Avg/Max/Min Temperature: {_avg}/{_max}/{_min}");
    }
}