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Mobius Core Library

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/*
 * -\-\-
 * Mobius
 * --
 * Copyright (c) 2017-2018 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;

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

import java.util.ArrayList;
import java.util.List;

/**
 * Provides a connection that queues up messages until a delegate to consume them is available.
 * Useful for setting up circular dependencies safely. All methods are synchronized for ease of
 * implementation.
 */
class QueuingConnection implements Connection {

  private final List queue = new ArrayList<>();

  private Connection delegate;
  private boolean disposed = false;

  synchronized void setDelegate(Connection delegate) {
    if (this.delegate != null) {
      throw new IllegalStateException("Attempt at setting delegate twice");
    }

    this.delegate = checkNotNull(delegate);

    if (disposed) {
      return;
    }

    for (I item : queue) {
      delegate.accept(item);
    }

    queue.clear();
  }

  @Override
  public synchronized void accept(I value) {
    if (delegate != null) {
      delegate.accept(value);
      return;
    }

    queue.add(value);
  }

  @Override
  public synchronized void dispose() {
    disposed = true;

    if (delegate != null) {
      delegate.dispose();
    }
  }
}