// deno-lint-ignore-file no-explicit-any
import { jit } from "./jit.ts";

export class Emitter<F extends (...args: any) => void> {
  #ls: { f: F; once: boolean }[] = [];
  #argc = 0;

  get argc() {
    return this.#argc;
  }

  get size() {
    return this.#ls.length;
  }

  constructor() {
    this.emit = this.#emit_fast;
  }

  on(f: F, once: boolean) {
    this.#ls.push({ f, once });
    this.#argc = Math.max(this.#argc, f.length);

    if (once) this.emit = this.#emit_slow;
    else this.#emit_fast = this.#compile();
    if (this.emit !== this.#emit_slow) this.emit = this.#emit_fast;
    return this;
  }

  off(f: F) {
    const ls = this.#ls;
    let once = false;

    for (let i = ls.length; i-- !== 0; ) {
      if (ls[i].f === f) {
        (once = ls[i].once), ls.splice(i, 1);
        break;
      }
    }

    this.#argc = ls.length ? Math.max(...ls.map(({ f }) => f.length)) : 0;
    if (!once) this.#emit_fast = this.#compile();
    if (this.emit !== this.#emit_slow) this.emit = this.#emit_fast;
    return this;
  }

  // deno-lint-ignore no-unused-vars
  emit(...args: Parameters<F>) {
    return false;
  }

  listeners() {
    return this.#ls.map(({ f }) => f);
  }

  #emit_fast = this.#compile();
  #emit_slow(...args: Parameters<F>) {
    const ls = this.#ls;
    (this.#ls = ls.filter(({ once }) => !once)), (this.emit = this.#emit_fast);

    for (let i = 0, n = ls.length; i < n; i++)
      Reflect.apply(ls[i].f, undefined, args);

    return ls.length !== 0;
  }

  #compile(): typeof this.emit {
    const ls = this.#ls.filter(({ once }) => !once);
    const ps = [...Array(this.#argc).keys()].map((i) => jit.raw`a${i}`);

    return jit.compiled`function emit(${jit.fragment(", ", ...ps)}) {
      ${jit.map(" ", ls, ({ f }) => {
        return jit`${f}(${jit.fragment(", ", ...ps.slice(0, f.length))});`;
      })}
      return ${ls.length !== 0};
    }`;
  }
}

export type EventMap = Record<string | symbol, (...args: any) => void>;

export class TypedEmitter<T extends EventMap> {
  readonly #events: { [K in keyof T]?: Emitter<T[K]> } = Object.create(null);

  on<K extends keyof T>(name: K, f: T[K]) {
    return (this.#events[name] ??= new Emitter()).on(f, false), this;
  }

  once<K extends keyof T>(name: K, f: T[K]) {
    return (this.#events[name] ??= new Emitter()).on(f, true), this;
  }

  off<K extends keyof T>(name: K, f: T[K]) {
    const events = this.#events;
    if (events[name]?.off(f).size === 0) delete events[name];
    return this;
  }

  emit<K extends keyof T>(name: K, ...args: Parameters<T[K]>) {
    const event = this.#events[name];
    if (event) return event.emit.apply(event, args);
    else return false;
  }

  listeners<K extends keyof T>(name: K) {
    return this.#events[name]?.listeners() ?? [];
  }

  static {
    this.prototype.emit = function emit(
      this: TypedEmitter<EventMap>,
      name: string,
      a: any,
      b: any,
      c: any,
      d: any,
      e: any
    ) {
      const event = this.#events[name];
      if (!event) return false;

      const { argc } = event;
      if (argc < 6) {
        return event.emit(a, b, c, d, e);
      } else {
        const args = Array(argc);
        for (let i = 0; i < argc; i++) args[i] = arguments[i + 1];
        return event.emit.apply(undefined, args);
      }
    } as any;
  }
}