content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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.datastax.oss.driver.api.core;
  
  import com.datastax.oss.driver.api.core.cql.ColumnDefinitions;
  import com.datastax.oss.driver.api.core.cql.ExecutionInfo;
  import com.datastax.oss.driver.internal.core.AsyncPagingIterableWrapper;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  import java.util.Iterator;
  import java.util.concurrent.CompletionStage;
  import java.util.function.Function;
  
  /**
   * An iterable of elements which are fetched asynchronously by the driver, possibly in multiple
   * requests.
   */
  public interface AsyncPagingIterable<ElementT, SelfT extends AsyncPagingIterable<ElementT, SelfT>> {
  
    /** Metadata about the columns returned by the CQL request that was used to build this result. */
    @NonNull
    ColumnDefinitions getColumnDefinitions();
  
    /** Returns {@linkplain ExecutionInfo information about the execution} of this page of results. */
    @NonNull
    ExecutionInfo getExecutionInfo();
  
    /** How many rows are left before the current page is exhausted. */
    int remaining();
  
    /**
     * The elements in the current page. To keep iterating beyond that, use {@link #hasMorePages()}
     * and {@link #fetchNextPage()}.
     *
     * <p>Note that this method always returns the same object, and that that object can only be
     * iterated once: elements are "consumed" as they are read.
     */
    @NonNull
    Iterable<ElementT> currentPage();
  
    /**
     * Returns the next element, or {@code null} if the results are exhausted.
     *
     * <p>This is convenient for queries that are known to return exactly one element, for example
     * count queries.
     */
    @Nullable
    default ElementT one() {
      Iterator<ElementT> iterator = currentPage().iterator();
      return iterator.hasNext() ? iterator.next() : null;
    }
  
    /**
     * Whether there are more pages of results. If so, call {@link #fetchNextPage()} to fetch the next
     * one asynchronously.
     */
    boolean hasMorePages();
  
    /**
     * Fetch the next page of results asynchronously.
     *
     * @throws IllegalStateException if there are no more pages. Use {@link #hasMorePages()} to check
     *     if you can call this method.
     */
    @NonNull
    CompletionStage<SelfT> fetchNextPage() throws IllegalStateException;
  
    /**
     * If the query that produced this result was a CQL conditional update, indicate whether it was
     * successfully applied.
     *
     * <p>For consistency, this method always returns {@code true} for non-conditional queries
     * (although there is no reason to call the method in that case). This is also the case for
     * conditional DDL statements ({@code CREATE KEYSPACE... IF NOT EXISTS}, {@code CREATE TABLE... IF
     * NOT EXISTS}), for which Cassandra doesn't return an {@code [applied]} column.
     *
     * <p>Note that, for versions of Cassandra strictly lower than 2.1.0-rc2, a server-side bug (<a
     * href="https://issues.apache.org/jira/browse/CASSANDRA-7337">CASSANDRA-7337</a>) causes this
     * method to always return {@code true} for batches containing conditional queries.
     */
    boolean wasApplied();
  
    /**
     * Creates a new instance by transforming each element of this iterable with the provided
     * function.
     *
     * <p>Note that both instances share the same underlying data: consuming elements from the
     * transformed iterable will also consume them from this object, and vice-versa.
     */
    default <TargetT> MappedAsyncPagingIterable<TargetT> map(
        Function<? super ElementT, ? extends TargetT> elementMapper) {
      return new AsyncPagingIterableWrapper<>(this, elementMapper);
    }
  }
  