/** @license
 *  Copyright 2016 - present The Material Motion Authors. All Rights Reserved.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may not
 *  use this file except in compliance with the License. You may obtain a copy
 *  of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 *  License for the specific language governing permissions and limitations
 *  under the License.
 */

import {
  MotionObservable,
} from '../observables/proxies';

import {
  Constructor,
  Observable,
  ObservableWithMotionOperators,
  Observer,
} from '../types';

import {
  isDefined,
} from '../typeGuards';

import {
  createPlucker,
} from './pluck';

export type MergeArgs<T> = {
  others: Array<Observable<T>>,
};

export interface MotionMergeable<T> extends Observable<T> {
  merge(kwargs: MergeArgs<T>): ObservableWithMotionOperators<T>;
  merge(others: Array<Observable<T>>): ObservableWithMotionOperators<T>;
}

export function withMerge<T, S extends Constructor<Observable<T>>>(superclass: S): S & Constructor<MotionMergeable<T>> {
  return class extends superclass implements MotionMergeable<T> {
    /**
     * Emits values as it receives them, both from upstream and from any
     * streams provided as arguments.
     */
    merge(kwargs: MergeArgs<T>): ObservableWithMotionOperators<T>;
    merge(others: Array<Observable<T>>): ObservableWithMotionOperators<T>;
    merge({ others }: MergeArgs<T> & Array<Observable<T>>): ObservableWithMotionOperators<T> {
      if (!isDefined(others)) {
        others = arguments[0];
      }

      return new MotionObservable(
        (observer: Observer<T>) => {
          const subscriptions = [this, ...others].map(
            stream => stream.subscribe(observer)
          );

          return () => {
            subscriptions.forEach(
              subscription => subscription.unsubscribe()
            );
          };
        }
      );
    }
  };
}