<?php
/*
 * Copyright 2016 Google LLC
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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.
 *     * Neither the name of Google Inc. 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
 * OWNER 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.
 */
namespace Google\ApiCore;

use Generator;
use InvalidArgumentException;
use IteratorAggregate;
use LengthException;

/**
 * A collection of elements retrieved using one or more API calls. The
 * collection will attempt to retrieve a fixed number of elements, and
 * will make API calls until that fixed number is reached, or there
 * are no more elements to retrieve.
 */
class FixedSizeCollection implements IteratorAggregate
{
    private $collectionSize;
    private $pageList;

    /**
     * FixedSizeCollection constructor.
     * @param Page $initialPage
     * @param integer $collectionSize
     */
    public function __construct($initialPage, $collectionSize)
    {
        if ($collectionSize <= 0) {
            throw new InvalidArgumentException(
                "collectionSize must be > 0. collectionSize: $collectionSize"
            );
        }
        if ($collectionSize < $initialPage->getPageElementCount()) {
            $ipc = $initialPage->getPageElementCount();
            throw new InvalidArgumentException(
                "collectionSize must be greater than or equal to the number of " .
                "elements in initialPage. collectionSize: $collectionSize, " .
                "initialPage size: $ipc"
            );
        }
        $this->collectionSize = $collectionSize;

        $this->pageList = FixedSizeCollection::createPageArray($initialPage, $collectionSize);
    }

    /**
     * Returns the number of elements in the collection. This will be
     * equal to the collectionSize parameter used at construction
     * unless there are no elements remaining to be retrieved.
     *
     * @return int
     */
    public function getCollectionSize()
    {
        $size = 0;
        foreach ($this->pageList as $page) {
            $size += $page->getPageElementCount();
        }
        return $size;
    }

    /**
     * Returns true if there are more elements that can be retrieved
     * from the API.
     *
     * @return bool
     */
    public function hasNextCollection()
    {
        return $this->getLastPage()->hasNextPage();
    }

    /**
     * Returns a page token that can be passed into the API list
     * method to retrieve additional elements.
     *
     * @return string
     */
    public function getNextPageToken()
    {
        return $this->getLastPage()->getNextPageToken();
    }

    /**
     * Retrieves the next FixedSizeCollection using one or more API calls.
     *
     * @return FixedSizeCollection
     */
    public function getNextCollection()
    {
        $lastPage = $this->getLastPage();
        $nextPage = $lastPage->getNextPage($this->collectionSize);
        return new FixedSizeCollection($nextPage, $this->collectionSize);
    }

    /**
     * Returns an iterator over the elements of the collection.
     *
     * @return Generator
     */
    public function getIterator()
    {
        foreach ($this->pageList as $page) {
            foreach ($page as $element) {
                yield $element;
            }
        }
    }

    /**
     * Returns an iterator over FixedSizeCollections, starting with this
     * and making API calls as required until all of the elements have
     * been retrieved.
     *
     * @return Generator|FixedSizeCollection[]
     */
    public function iterateCollections()
    {
        $currentCollection = $this;
        yield $this;
        while ($currentCollection->hasNextCollection()) {
            $currentCollection = $currentCollection->getNextCollection();
            yield $currentCollection;
        }
    }

    private function getLastPage()
    {
        $pageList = $this->pageList;
        // Get last element in array...
        $lastPage = end($pageList);
        reset($pageList);
        return $lastPage;
    }

    /**
     * @param Page $initialPage
     * @param integer $collectionSize
     * @return Page[]
     */
    private static function createPageArray($initialPage, $collectionSize)
    {
        $pageList = [$initialPage];
        $currentPage = $initialPage;
        $itemCount = $currentPage->getPageElementCount();
        while ($itemCount < $collectionSize && $currentPage->hasNextPage()) {
            $remainingCount = $collectionSize - $itemCount;
            $currentPage = $currentPage->getNextPage($remainingCount);
            $rxElementCount = $currentPage->getPageElementCount();
            if ($rxElementCount > $remainingCount) {
                throw new LengthException("API returned a number of elements " .
                    "exceeding the specified page size limit. page size: " .
                    "$remainingCount, elements received: $rxElementCount");
            }
            array_push($pageList, $currentPage);
            $itemCount += $rxElementCount;
        }
        return $pageList;
    }
}