Observer-pattern.ts

/**
 * @author Gadzhiev Islam
 * 
 * Considering we can make the design cleaner, how to refactor this code ?
 * What improvements could be done in order to comply with responsibilities and logic of observability ?
 */

interface Subject{
    registerObserver(o: Observer): void;
    removeObserver(o: Observer): void;
    notifyObservers(): void;
}

interface Observer{
    update(temperature: number): void;
}

class WeatherStation implements Subject {
    private observers: Observer[] = [];
    private temperature: number;
    registerObserver(o: Observer) {
        this.observers.push(o);
    }
    removeObserver(o: Observer) {
        let index = this.observers.indexOf(o);
        this.observers.splice(index, 1);
    }
    notifyObservers() {
        for (let observer of this.observers) {
            observer.update(this.temperature);
        }
    }
    setTemperature(temp: number) {
        console.log('WeatherStation: new temperature measurement: ' + temp, '\n');
        this.temperature = temp;
        this.notifyObservers();
    }
}

class TemperatureDisplay implements Observer {
    private subject: Subject;
    constructor(weatherStation: Subject) {
        this.subject = weatherStation;
        weatherStation.registerObserver(this);
    }
    update(temperature: number) {
        console.log('TemperatureDisplay: I need to update my display', '\n');
    }
}

class Fan implements Observer {
    private subject: Subject;
    constructor(weatherStation: Subject) {
        this.subject = weatherStation;
        weatherStation.registerObserver(this);
    }
    update(temperature: number) {
        if (temperature > 25) {
            console.log('Fan: Its hot here, turning myself on...', '\n');
        } else {
            console.log('Fan: Its nice and cool, turning myself off...', '\n');
        }
    }
}

let weatherStation = new WeatherStation();
let tempDisplay = new TemperatureDisplay(weatherStation);
let fan = new Fan(weatherStation);

weatherStation.setTemperature(20);
weatherStation.setTemperature(30);