export type Listener<Data, Key extends keyof Data> = (
  data: Data[Key],
  key: Key
) => void;
export type AnyListener<Data> = (data: Partial<Data>, key: string) => void;
export type Unsubscribe = () => void;

export interface PropertyChange<Source, Value> {
  source: Source;
  previous: Value;
}

export interface AnyEvent<Data> {
  key: string;
  data: Partial<Data>;
}

export interface Events<Data> {
  on<Key extends keyof Data>(
    eventKey: Key,
    listener: Listener<Data, Key>
  ): void;
  off<Key extends keyof Data>(
    eventKey: Key,
    listener: Listener<Data, Key>
  ): void;
  onAny(listener: AnyListener<Data>): void;
  offAny(listener: AnyListener<Data>): void;
}

export class EventSource<Data> implements Events<Data> {
  private listeners = new Map<keyof Data, Listener<Data, any>[]>();
  private anyListeners: AnyListener<Data>[] | undefined;

  on<Key extends keyof Data>(
    eventKey: Key,
    listener: Listener<Data, Key>
  ): void {
    let listeners = this.listeners.get(eventKey);
    if (!listeners) {
      listeners = [];
      this.listeners.set(eventKey, listeners);
    }
    listeners.push(listener);
  }

  onAny(listener: AnyListener<Data>): void {
    let listeners = this.anyListeners;
    if (!listeners) {
      listeners = [];
      this.anyListeners = listeners;
    }
    listeners.push(listener);
  }

  off<Key extends keyof Data>(
    eventKey: Key,
    listener: Listener<Data, Key>
  ): void {
    const listeners = this.listeners.get(eventKey);
    if (!listeners) {
      return;
    }
    const index = listeners.indexOf(listener);
    if (index >= 0) {
      listeners.splice(index, 1);
    }
  }

  offAny(listener: AnyListener<Data>): void {
    const listeners = this.anyListeners;
    if (!listeners) {
      return;
    }
    const index = listeners.indexOf(listener);
    if (index >= 0) {
      listeners.splice(index, 1);
    }
  }

  trigger<Key extends keyof Data>(eventKey: Key, data: Data[Key]): void {
    const listeners = this.listeners.get(eventKey);
    if (listeners) {
      for (const listener of listeners) {
        listener(data, eventKey);
      }
    }

    if (this.anyListeners) {
      for (const anyListener of this.anyListeners) {
        anyListener({ [eventKey]: data } as any, eventKey as string);
      }
    }
  }
}

export class EventObserver {
  private unsubscribeByKey = new Map<string, Unsubscribe[]>();
  private onDispose: Unsubscribe[] = [];

  listen<Data, Key extends keyof Data>(
    events: Events<Data>,
    eventKey: Key,
    listener: Listener<Data, Key>
  ) {
    events.on(eventKey, listener);
    this.onDispose.push(() => events.off(eventKey, listener));
  }

  listenAny<Data>(events: Events<Data>, listener: AnyListener<Data>) {
    events.onAny(listener);
    this.onDispose.push(() => events.offAny(listener));
  }

  listenOnce<Data, Key extends keyof Data>(
    events: Events<Data>,
    eventKey: Key,
    listener: Listener<Data, Key>
  ) {
    let handled = false;
    const onceListener: Listener<Data, Key> = (data, key) => {
      handled = true;
      events.off(eventKey, onceListener);
      listener(data, key);
    };
    events.on(eventKey, onceListener);
    this.onDispose.push(() => {
      if (handled) {
        return;
      }
      events.off(eventKey, onceListener);
    });
  }

  stopListening() {
    for (const unsubscribe of this.onDispose) {
      unsubscribe();
    }
    this.onDispose.length = 0;

    this.unsubscribeByKey.forEach((unsubscribers) => {
      for (const unsubscribe of unsubscribers) {
        unsubscribe();
      }
    });
    this.unsubscribeByKey.clear();
  }
}