mediator pattern

mediator_pattern.go

package main

import "fmt"

type airplane interface {
    arrive()
    depart()
    permitArrival()
}

type mediator interface {
    canArrive(airplane) bool
    notifyAboutDeparture()
}


type passenger struct {
    mediator mediator
}

func (p *passenger) arrive() {
    if !p.mediator.canArrive(p) {
        fmt.Println("airplane passenger: Arrival blocked, waiting")
        return
    }
    fmt.Println("airplane passenger: Arrived")
}

func (p *passenger) depart() {
    fmt.Println("airplane passenger: Leaving")
    p.mediator.notifyAboutDeparture()
}

func (p *passenger) permitArrival() {
    fmt.Println("airplane passenger: landing permitted, arriving")
    p.arrive()
}


type boeing737 struct {
    mediator mediator
}

func (b *boeing737) arrive() {
    if !b.mediator.canArrive(b) {
        fmt.Println("boeing 737: Landing blocked, waiting")
        return
    }
    fmt.Println("boeing 737: Arrived")
}

func (b *boeing737) depart() {
    fmt.Println("boeing 737: Taking off")
    b.mediator.notifyAboutDeparture()
}

func (b *boeing737) permitArrival() {
    fmt.Println("boeing 737: Arrival permitted")
    b.arrive()
}


type airportManager struct {
    isRunwayFree bool
    airportQueue []airplane
}

func newStationManager() *airportManager {
    return &airportManager{
        isRunwayFree: true,
    }
}

func (a *airportManager) canArrive(p airplane) bool {
    if a.isRunwayFree {
        a.isRunwayFree = false
        return true
    }
    a.airportQueue = append(a.airportQueue, p)
    return false
}

func (a *airportManager) notifyAboutDeparture() {
    if !a.isRunwayFree {
        a.isRunwayFree = true
    }
    if len(a.airportQueue) > 0 {
        firstAirplaneInQueue := a.airportQueue[0]
        a.airportQueue = a.airportQueue[1:]
        firstAirplaneInQueue.permitArrival()
    }
}

func main() {
    stationManager := newStationManager()
    
    airplanePassenger := &passenger{
        mediator: stationManager,
    }
    
    boeing := &boeing737{
        mediator: stationManager,
    }
    
    airplanePassenger.arrive()
    boeing.arrive()
    airplanePassenger.depart()
}

// output:
// airplane passenger: Arrived
// boeing 737: Landing blocked, waiting
// airplane passenger: Leaving
// boeing 737: Arrival permitted
// boeing 737: Arrived