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Fluent, object-oriented Java API for YouTrack.
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/*
 * Copyright 2017 George Aristy
 *
 * 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 org.llorllale.youtrack.api;

import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.apache.http.client.HttpClient;

import org.apache.http.client.methods.HttpUriRequest;

/**
 * An {@link Iterator} that holds the contents of a single page of results from the YouTrack server.
 * 
 * Note: the {@link #hasNext()} and {@link #next()} methods wrap checked exceptions inside
 * {@link UncheckedException}.
 * 
 * @author George Aristy ([email protected])
 * @param  the type of the contents of this page
 * @see Pagination
 * @since 0.7.0
 */
final class Page implements Iterator {
  private final Deque contents;

  /**
   * Ctor.
   * 
   * @param request the {@link HttpUriRequest} for the page
   * @param mapper the mapping function to transform the results from YouTrack into types T
   * @param httpClient the {@link HttpClient} to use
   * @throws UncheckedException wrapping any IOException thrown when fetching this page's contents
   * @since 0.7.0
   */
  Page(
      HttpUriRequest request, 
      ExceptionalFunction, IOException> mapper,
      HttpClient httpClient
  ) throws UncheckedException {
    try {
      this.contents = new ArrayDeque<>(
          mapper.apply(
              new HttpResponseAsResponse(
                  httpClient.execute(request)
              )
          )
      );
    } catch (IOException e) {
      throw new UncheckedException(e);
    }
  }

  @Override
  public boolean hasNext() {
    return !this.contents.isEmpty();
  }

  @Override
  public T next() {
    if (this.hasNext()) {
      return this.contents.pop();
    }

    throw new NoSuchElementException();
  }

  /**
   * Special {@link Page} that always returns {@code false} from {@link #hasNext()} and throws a
   * {@link NoSuchElementException} from {@link #next()}.
   * 
   * @param  the type parameter for the results enclosed
   * @since 0.7.0
   */
  static final class Empty implements Iterator {
    @Override
    public boolean hasNext() {
      return false;
    }

    @Override
    public T next() {
      throw new NoSuchElementException();
    }
  }
}