Observer

ObserverPattern.ts

interface Observer {
  update: () => void;
}

interface Subject {
  subscribe: (observer: Observer) => void,
  unsubscribe: (observer: Observer) => void,
  notify: () => void,
}

interface IWeatherStation extends Subject {
  updateTemperature: (value: number) => void,
}

const WeatherStation = (): IWeatherStation => {
  let temperature = 0
  let observers: Observer[] = []

  const updateTemperature = (value) => {
    temperature = value
    notify()
  }

  const subscribe = (observer) => observers.push(observer)
  const unsubscribe = (observer) => observers = observers.filter(o => o !== observer) 
  const notify = () => observers.forEach(o => o.update())

  return {
    updateTemperature,
    subscribe,
    unsubscribe,
    notify,
  }
}

const Cooler = (name: string): Observer => {
  const state = { name }

  return{
    update: () => console.log("Realizando checks de ventilação...", state.name)
  }
}

const Display = (): Observer => {
  return{
    update: () => console.log("Recebi a atualização")
  }
}

const weatherStation = WeatherStation()
const cooler1 = Cooler('cooler1')
const cooler2 = Cooler('cooler2')
const cooler3 = Cooler('cooler3')
const display = Display()

weatherStation.subscribe(cooler1)
weatherStation.subscribe(cooler2)
weatherStation.subscribe(cooler3)
weatherStation.subscribe(display)

weatherStation.updateTemperature(10)