import { Transform, TransformOptions } from "stream";
import { types } from "util";

export type Mapper = (
  this: Transform,
  chunk: any,
  encoding: string,
  callback?: (err?: any, data?: any) => void
) => any;

export class Map extends Transform {
  private _map: Mapper;

  constructor(map: Mapper, options?: TransformOptions) {
    super(options);
    this._map = map;
  }

  _transform(chunk: Buffer | string, encoding: string, callback: (err?: any, data?: any) => void) {
    if (this._map.length >= 3) {
      const out = this._map.call(this, chunk, encoding, callback);

      if (types.isPromise(out)) {
        process.nextTick(() => {
          this.emit("error", new Error("Resolution method is overspeciied"));
        });
      }
    } else {
      const out = this._map.call(this, chunk, encoding);

      if (types.isPromise(out)) {
        out.then(data => callback(null, data)).catch(callback);
      } else {
        callback(null, out);
      }
    }
  }
}