EventDispatcher.kt

package jonnothebonno.me.veggiebeers.events

import jonnothebonno.me.veggiebeers.util.guard

typealias EventList = MutableList<EventType>
typealias EventObservers = MutableMap<EventDispatchObserver, EventList>

class EventDispatcher private constructor() : EventDispatcherContract {
    val observers: EventObservers = mutableMapOf()

    companion object {
        val instance by lazy { EventDispatcher() }
    }

    override fun dispatchEvent(event: EventType) {
        observers.forEach { key, value ->
            if (value.contains(event)) {
                key.didReceiveEvent(event)
            }
        }
    }

    override fun addObserver(observer: EventDispatchObserver, event: EventType) {
        observers[observer].guard { observers[observer] = mutableListOf() }
        observers[observer]?.add(event)
    }

    override fun removeObserver(observer: EventDispatchObserver) {
        observers.remove(observer)
    }
}

EventDispatcherContract.kt

package jonnothebonno.me.veggiebeers.events

interface EventDispatcherContract {
    fun dispatchEvent(event: EventType)
    fun addObserver(observer: EventDispatchObserver, event: EventType)
    fun removeObserver(observer: EventDispatchObserver)
}

EventDispatchObserver.kt

package jonnothebonno.me.veggiebeers.events

interface EventDispatchObserver {
    fun didReceiveEvent(event: EventType)
}

EventType.kt

package jonnothebonno.me.veggiebeers.events

enum class EventType {
    IAP_NOT_AVAILABLE
}