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/* EE-TS Types for mapping interface of functions */
type In<T> = T extends (...args: infer U) => any ? U : [];type Out<T> = T extends (...args: any[]) => infer U ? U : never;
type Filter<T, Cond, U extends keyof T = keyof T> = {  [K in U]: T[K] extends Cond ? K : never;}[U];
type EventKey<T> = Filter<T, (...args: any[]) => any> & string;
type EventIn<T, K extends EventKey<T>> = In<T[K]>;type EventOut<T, K extends EventKey<T>> = Out<T[K]> | void;
type Listener<T, K extends EventKey<T> = EventKey<T>> = (  ...args: EventIn<T, K>) => EventOut<T, K>;
interface IListener<T, K extends EventKey<T> = EventKey<T>> {  fn: Listener<T, K>;  once: boolean;}
export class EventEmitter<T> {  private listeners: { [K in EventKey<T>]?: IListener<T, K>[] } = {};  public on<K extends EventKey<T>>(key: K, fn: Listener<T, K>): this;  public on(arg: EventKey<T>, fn: Listener<T>): this {    if (this.listeners[arg] === undefined) {      this.listeners[arg] = [];    }    const listeners = this.listeners[arg];    if (listeners !== undefined) {      listeners.push({        fn,        once: false,      });    }    return this;  }  public once<K extends EventKey<T>>(key: K, fn: Listener<T, K>): this;  public once(arg: EventKey<T>, fn: Listener<T>): this {    if (this.listeners[arg] === undefined) {      this.listeners[arg] = [];    }    const listeners = this.listeners[arg];    if (listeners !== undefined) {      listeners.push({        fn,        once: true,      });    }    return this;  }  public emit<K extends EventKey<T>>(    key: K,    ...args: EventIn<T, K>  ): EventOut<T, K>;  public emit<K extends EventKey<T>>(key: K, ...args: EventIn<T, K>): any {    let result;    let gen = this.getListeners(key);    while (true) {      let { value: listener, done } = gen.next();      if (done) {        return result;      } else {        let generated = listener(...args);        if (generated !== undefined) {          result = generated;        }      }    }  }  public removeListener<K extends EventKey<T>>(    key: K,    listener: Listener<T, K>,  ): boolean {    const list = this.listeners[key];    if (list === undefined) return false;    let splice = -1;    list.some((val, i) => {      if (val.fn.toString() === listener.toString()) {        splice = i;        return true;      }    });    if (splice === -1) return false;    list.splice(splice, 1);    return true;  }  public removeListeners<K extends EventKey<T>>(key: K): boolean {    const list = this.listeners[key];    if (list === undefined) return false;    delete this.listeners[key];    return true;  }  public removeAllListeners(): void {    this.listeners = {};  }  *getListeners<K extends EventKey<T>>(    key: K,  ): IterableIterator<Listener<T, K>> {    const list = this.listeners[key];    if (list === undefined) return;    for (let i = 0; i < list.length; i++) {      const listener = list[i];      yield listener.fn;    }    this.listeners[key] = list.filter((listener) => !listener.once);  }}
export default EventEmitter;