export class Event {
    constructor(name) {
        this.name = name
        this.subscriptions = []
    }

    subscribe(handler) {
        if ( typeof handler !== 'function' ) {
            throw new TypeError('Event subscription handler must be a function')
        }

        this.subscriptions.push(handler)
        return () => this.subscriptions = this.subscriptions.filter(x => x !== handler)
    }

    async fire(...args) {
        return Promise.all(this.subscriptions.map(x => x(...args)))
    }
}

export class EventBus {
    static get() {
        if ( !this.instance ) {
            this.instance = new EventBus()
        }

        return this.instance
    }

    constructor() {
        this.events = []
    }

    /** @return Event */
    event(name) {
        if ( !this.events[name] ) {
            this.events[name] = new Event(name)
        }

        return this.events[name]
    }
}