stream-chain/utils/skipWhile.js

'use strict';

const {Transform} = require('stream');

const alwaysFalse = () => false;

class SkipWhile extends Transform {
  constructor(options) {
    super(Object.assign({}, options, {writableObjectMode: true, readableObjectMode: true}));
    this._condition = alwaysFalse;
    if (options) {
      'condition' in options && (this._condition = options.condition);
    }
  }
  _transform(chunk, encoding, callback) {
    const result = this._condition.call(this, chunk);
    if (result && typeof result.then == 'function') {
      result.then(
        flag => {
          if (!flag) {
            this._transform = this._passThrough;
            this.push(chunk);
          }
          callback(null);
        },
        error => callback(error)
      );
    } else {
      if (!result) {
        this._transform = this._passThrough;
        this.push(chunk);
      }
      callback(null);
    }
  }
  _passThrough(chunk, encoding, callback) {
    this.push(chunk);
    callback(null);
  }
  static make(condition) {
    return new SkipWhile(typeof condition == 'object' ? condition : {condition});
  }
}
SkipWhile.make.Constructor = SkipWhile;

module.exports = SkipWhile.make;