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RxJava2 utilities for use with Mobius

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/*
 * -\-\-
 * Mobius
 * --
 * Copyright (c) 2017-2020 Spotify AB
 * --
 * 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.
 * -/-/-
 */
package com.spotify.mobius.rx2;

import static com.spotify.mobius.internal_util.Preconditions.checkNotNull;

import io.reactivex.Observable;
import io.reactivex.ObservableTransformer;
import io.reactivex.functions.Function;
import java.util.ArrayList;
import java.util.List;

/**
 * Utility that dispatches each item emitted from a source observable of type T to multiple other
 * ObservableTransformers, and merges the results to a stream of type R.
 *
 * @param  input type
 * @param  output type
 */
class MergedTransformer implements ObservableTransformer {

  private final Iterable> transformers;

  public MergedTransformer(Iterable> transformers) {
    this.transformers = checkNotNull(transformers);
  }

  @Override
  public Observable apply(Observable input) {
    return input.publish(
        new Function, Observable>() {
          @Override
          public Observable apply(Observable innerInput) {
            final List> transformed = new ArrayList<>();
            for (ObservableTransformer transformer : transformers) {
              transformed.add(innerInput.compose(transformer));
            }
            return Observable.merge(transformed);
          }
        });
  }
}