9.3.6 الگو Observer

package main

import "fmt"

// Observer interface
type Observer interface {
    Update(temperature float64)
}

// Subject interface
type Subject interface {
    RegisterObserver(o Observer)
    RemoveObserver(o Observer)
    NotifyObservers()
}

// Concrete Subject - WeatherStation
type WeatherStation struct {
    temperature float64
    observers   []Observer
}

func (w *WeatherStation) RegisterObserver(o Observer) {
    w.observers = append(w.observers, o)
}

func (w *WeatherStation) RemoveObserver(o Observer) {
    for i, observer := range w.observers {
        if observer == o {
            w.observers = append(w.observers[:i], w.observers[i+1:]...)
            break
        }
    }
}

func (w *WeatherStation) NotifyObservers() {
    for _, observer := range w.observers {
        observer.Update(w.temperature)
    }
}

func (w *WeatherStation) SetTemperature(temp float64) {
    w.temperature = temp
    w.NotifyObservers() // Notify all observers when temperature changes
}

// Concrete Observer - PhoneDisplay
type PhoneDisplay struct {
    id string
}

func (p *PhoneDisplay) Update(temperature float64) {
    fmt.Printf("Phone Display %s: Temperature is %.1f°C\n", p.id, temperature)
}

// Concrete Observer - TVDisplay
type TVDisplay struct {
    channel string
}

func (t *TVDisplay) Update(temperature float64) {
    fmt.Printf("TV Display on %s: Current temperature: %.1f°C\n", t.channel, temperature)
}

func main() {
    // Create the subject (weather station)
    weatherStation := &WeatherStation{}
    
    // Create observers
    phone1 := &PhoneDisplay{id: "1"}
    phone2 := &PhoneDisplay{id: "2"}
    tv := &TVDisplay{channel: "Weather Channel"}
    
    // Register observers
    weatherStation.RegisterObserver(phone1)
    weatherStation.RegisterObserver(phone2)
    weatherStation.RegisterObserver(tv)
    
    // Change temperature - all observers get notified
    fmt.Println("Setting temperature to 25.5°C:")
    weatherStation.SetTemperature(25.5)
    
    fmt.Println("\nSetting temperature to 30.2°C:")
    weatherStation.SetTemperature(30.2)
    
    // Remove one observer
    fmt.Println("\nRemoving Phone Display 2 and setting temperature to 28.0°C:")
    weatherStation.RemoveObserver(phone2)
    weatherStation.SetTemperature(28.0)
}

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