// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.
/*-----------------------------------------------------------------------------
| Copyright (c) 2014-2017, PhosphorJS Contributors
|
| Distributed under the terms of the BSD 3-Clause License.
|
| The full license is in the file LICENSE, distributed with this software.
|----------------------------------------------------------------------------*/
import { IIterator, iter, IterableOrArrayLike } from './iter';

/**
 * Chain together several iterables.
 *
 * @param objects - The iterable or array-like objects of interest.
 *
 * @returns An iterator which yields the values of the iterables
 *   in the order in which they are supplied.
 *
 * #### Example
 * ```typescript
 * import { chain, toArray } from '@lumino/algorithm';
 *
 * let data1 = [1, 2, 3];
 * let data2 = [4, 5, 6];
 *
 * let stream = chain(data1, data2);
 *
 * toArray(stream);  // [1, 2, 3, 4, 5, 6]
 * ```
 */
export function chain<T>(...objects: IterableOrArrayLike<T>[]): IIterator<T> {
  return new ChainIterator<T>(iter(objects.map(iter)));
}

/**
 * An iterator which chains together several iterators.
 */
export class ChainIterator<T> implements IIterator<T> {
  /**
   * Construct a new chain iterator.
   *
   * @param source - The iterator of iterators of interest.
   */
  constructor(source: IIterator<IIterator<T>>) {
    this._source = source;
    this._active = undefined;
  }

  /**
   * Get an iterator over the object's values.
   *
   * @returns An iterator which yields the object's values.
   */
  iter(): IIterator<T> {
    return this;
  }

  /**
   * Create an independent clone of the iterator.
   *
   * @returns A new independent clone of the iterator.
   */
  clone(): IIterator<T> {
    let result = new ChainIterator<T>(this._source.clone());
    result._active = this._active && this._active.clone();
    result._cloned = true;
    this._cloned = true;
    return result;
  }

  /**
   * Get the next value from the iterator.
   *
   * @returns The next value from the iterator, or `undefined`.
   */
  next(): T | undefined {
    if (this._active === undefined) {
      let active = this._source.next();
      if (active === undefined) {
        return undefined;
      }
      this._active = this._cloned ? active.clone() : active;
    }
    let value = this._active.next();
    if (value !== undefined) {
      return value;
    }
    this._active = undefined;
    return this.next();
  }

  private _source: IIterator<IIterator<T>>;
  private _active: IIterator<T> | undefined;
  private _cloned = false;
}