// This module is browser-compatible.

// deno-lint-ignore-file ban-types

/**
 * An event emitter (observer pattern)
 */
export class EventEmitter {
    listeners = new Map<PropertyKey, Function[]>();

    #addListener(event: string, func: Function) {
        this.listeners.set(event, this.listeners.get(event) || []);
        this.listeners.get(event)?.push(func);
        return this;
    }

    on(event: string, func: Function) {
        return this.#addListener(event, func);
    }

    #removeListener(event: string, func: Function) {
        if (this.listeners.has(event)) {
            const listener = this.listeners.get(event);

            if (listener?.includes(func)) {
                listener.splice(listener.indexOf(func), 1);

                if (listener.length === 0) {
                    this.listeners.delete(event);
                }
            }
        }

        return this;
    }

    off(event: string, func: Function) {
        return this.#removeListener(event, func);
    }

    once(event: string, func: Function) {
        // it is important for this to be an arrow function
        const closure = () => {
            func();
            this.off(event, func);
        };

        const listener = this.listeners.get(event) ?? [];

        listener.push(closure);

        return this;
    }

    emit(event: string, ...args: unknown[]) {
        const listener = this.listeners.get(event);

        if (!listener) {
            return false;
        }

        listener.forEach((f) => f(...args));

        return true;
    }

    listenerCount(eventName: string) {
        return this.listeners.get(eventName)?.length ?? 0;
    }

    rawListeners(eventName: string): Function[] | undefined {
        return this.listeners.get(eventName);
    }
}

export default EventEmitter;