iter-tools-es/internal/bisector.js

The iterable toolbox

const {
  IterableIterator
} = require('./iterable-iterator.js');

const {
  PartsIterator
} = require('./parts-iterator.js');

class Bisector extends IterableIterator {
  constructor(source, strategy, options) {
    super();
    this.source = source;
    this.strategy = strategy;
    this.options = options;
    this.partsIterator = null;
    this.firstPart = null;
    this.secondPart = null;
    this.currentIdx = 0;
  }

  setupFirst() {
    const {
      source,
      strategy,
      options
    } = this;
    this.partsIterator = this.partsIterator || new PartsIterator(source, strategy, options);

    if (!this.firstPart) {
      const step = this.partsIterator.next();
      this.firstPart = step.done ? [] : step.value;
    }
  }

  next() {
    const self = this;

    switch (this.currentIdx++) {
      case 0:
        return {
          value: function* () {
            self.setupFirst();
            yield* self.firstPart;
          }(),
          done: false
        };

      case 1:
        return {
          value: function* () {
            self.setupFirst();
            const step = self.partsIterator.next();
            self.secondPart = step.done ? [] : step.value;
            yield* self.secondPart;
          }(),
          done: false
        };

      default:
        return {
          value: undefined,
          done: true
        };
    }
  }

  return() {
    if (this.currentIdx === 1) {
      throw new Error('You must take both parts of a bisector or neither.');
    }

    return {
      value: undefined,
      done: true
    };
  }

}

exports.Bisector = Bisector;