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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.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Function;
import java.util.function.Supplier;
import org.apache.http.client.HttpClient;

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

/**
 * An {@link Iterator} that encapsulates a paginated resource 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 resource's type
 * @see Page
 * @since 0.7.0
 */
final class Pagination implements Iterator {
  private final Supplier pageRequest;
  private final ExceptionalFunction, IOException> mapper;
  private final HttpClient httpClient;

  private Iterator page;

  /**
   * Ctor.
   * 
   * @param pageRequest the supplier for each {@link Page page's} uri
   * @param mapper maps each page's URI into its corresponding contents
   * @param httpClient the {@link HttpClient} to use to execute the requests
   * @since 0.7.0
   */
  Pagination(
      Supplier pageRequest,
      ExceptionalFunction, IOException> mapper,
      HttpClient httpClient
  ) {
    this.pageRequest = pageRequest;
    this.mapper = mapper;
    this.page = new Page.Empty<>();
    this.httpClient = httpClient;
  }

  /**
   * Constructs a {@link PageUri} by providing: a) a {@link Counter} with values 0 and 
   * {@code pageSize}, and the {@code combiner}.
   * 
   * @param pageSize the page size
   * @param combiner the function that maps page numbers to http requests
   * @param mapper the function that maps the resources to collections
   * @param httpClient the {@link HttpClient} to use to execute the requests
   * @see #Pagination(PageUri, ExceptionalFunction) 
   * @see PageUri
   * @since 1.0.0
   */
  Pagination(
      int pageSize,
      Function combiner, 
      ExceptionalFunction, IOException> mapper,
      HttpClient httpClient
  ) {
    this(new PageUri(new Counter(0, pageSize), combiner), mapper, httpClient);
  }

  @Override
  public boolean hasNext() {
    if (!this.page.hasNext()) {
      this.page = new Page<>(this.pageRequest.get(), this.mapper, this.httpClient);
    }

    return this.page.hasNext();
  }

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

    throw new NoSuchElementException();
  }
}