iter-tools-es/internal/peekerator.js

The iterable toolbox

const {
  ensureIterable,
  callReturn
} = require('./iterable.js');

const _ = Symbol.for('_');

class PeekeratorIterator {
  constructor(peekr) {
    this.peekr = peekr;
  }

  next() {
    const {
      peekr
    } = this;
    const {
      current
    } = peekr;
    peekr.advance();
    return current;
  }

  return() {
    this.peekr.return();
    return {
      value: undefined,
      done: true
    };
  }

  [Symbol.iterator]() {
    return this;
  }

}

class Peekerator {
  static from(iterable, ...args) {
    const iterator = ensureIterable(iterable)[Symbol.iterator]();
    const first = iterator.next();
    return new this(iterator, first, ...args);
  }

  constructor(iterator, first) {
    this[_] = {
      iterator,
      current: first,
      index: 0
    };
  }

  get current() {
    return this[_].current;
  }

  get value() {
    return this[_].current.value;
  }

  get done() {
    return this[_].current.done;
  }

  get index() {
    return this[_].index;
  }

  advance() {
    const this_ = this[_];

    if (!this_.current.done) {
      this_.index++;
      this_.current = this_.iterator.next();
    }

    return this;
  }

  return() {
    const this_ = this[_];

    if (!this.done) {
      callReturn(this_.iterator);
    }

    this_.current = {
      value: undefined,
      done: true
    };
    return this;
  }

  asIterator() {
    return new PeekeratorIterator(this);
  }

}

exports.Peekerator = Peekerator;