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/*
 * Copyright (c) 2015, PagerDuty
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of conditions
 * and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided with
 * the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.pagerduty.widerow.chain

import com.pagerduty.widerow.Entry
import scala.concurrent.{ExecutionContextExecutor, Future}


private[widerow] class PageMap[Source, Result](
    val wrapped: OpChain[Source],
    val mapping: IndexedSeq[Source] => Future[IndexedSeq[Result]])
  extends OpChain[Result]
{
  implicit val executor: ExecutionContextExecutor = wrapped.executor

  private def applyMapping(seq: IndexedSeq[Source]) = {
    // Avoids applying mapping to empty sequences.
    if (seq.isEmpty) Future.successful(IndexedSeq.empty)
    else mapping(seq)
  }

  def apply() = wrapped.apply().flatMap(applyMapping)
  def drain() = wrapped.drain().flatMap(applyMapping)

  def next(page: IndexedSeq[Entry[_, _, _]])
  :Future[OpChain[Result]] = {
    wrapped.next(page).map(wrappedOp => new PageMap(wrappedOp, mapping))
  }
}