iter-tools-es/internal/groups-iterator.js

The iterable toolbox

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

const {
  split
} = require('./symbols.js');

class GroupsIterator extends PartsIterator {
  next() {
    if (!this.initialized) this.init();
    const {
      spliterator
    } = this;

    if (this.currentPart !== null) {
      if (spliterator.value !== split || spliterator.current === this.splitStep) {
        this.currentPart.inactive = true;

        while (!spliterator.done && spliterator.value !== split) {
          spliterator.advance();
        }
      }
    }

    if (spliterator.done) {
      return {
        value: undefined,
        done: true
      };
    }

    spliterator.advance();

    if (spliterator.done || spliterator.value === split) {
      throw new Error('Unexpected empty group');
    }

    const key = spliterator.value;
    spliterator.advance();
    this.splitStep = spliterator.current;
    this.currentPart = new PartIterator(this);
    return {
      value: [key, this.currentPart],
      done: false
    };
  }

}

exports.GroupsIterator = GroupsIterator;