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<?php
/*
* Copyright 2017 MongoDB, Inc.
*
* 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.
*/
namespace MongoDB\Model;
use Countable;
use Generator;
use Iterator;
use Traversable;
/**
* Iterator for wrapping a Traversable and caching its results.
*
* By caching results, this iterators allows a Traversable to be counted and
* rewound multiple times, even if the wrapped object does not natively support
* those operations (e.g. MongoDB\Driver\Cursor).
*
* @internal
*/
class CachingIterator implements Countable, Iterator
{
private $items = [];
private $iterator;
private $iteratorAdvanced = false;
private $iteratorExhausted = false;
/**
* Constructor.
*
* Initialize the iterator and stores the first item in the cache. This
* effectively rewinds the Traversable and the wrapping Generator, which
* will execute up to its first yield statement. Additionally, this mimics
* behavior of the SPL iterators and allows users to omit an explicit call
* to rewind() before using the other methods.
*
* @param Traversable $traversable
*/
public function __construct(Traversable $traversable)
{
$this->iterator = $this->wrapTraversable($traversable);
$this->storeCurrentItem();
}
/**
* @see http://php.net/countable.count
* @return integer
*/
public function count()
{
$this->exhaustIterator();
return count($this->items);
}
/**
* @see http://php.net/iterator.current
* @return mixed
*/
public function current()
{
return current($this->items);
}
/**
* @see http://php.net/iterator.key
* @return mixed
*/
public function key()
{
return key($this->items);
}
/**
* @see http://php.net/iterator.next
* @return void
*/
public function next()
{
if ( ! $this->iteratorExhausted) {
$this->iterator->next();
$this->storeCurrentItem();
}
next($this->items);
}
/**
* @see http://php.net/iterator.rewind
* @return void
*/
public function rewind()
{
/* If the iterator has advanced, exhaust it now so that future iteration
* can rely on the cache.
*/
if ($this->iteratorAdvanced) {
$this->exhaustIterator();
}
reset($this->items);
}
/**
* @see http://php.net/iterator.valid
* @return boolean
*/
public function valid()
{
return $this->key() !== null;
}
/**
* Ensures that the inner iterator is fully consumed and cached.
*/
private function exhaustIterator()
{
while ( ! $this->iteratorExhausted) {
$this->next();
}
}
/**
* Stores the current item in the cache.
*/
private function storeCurrentItem()
{
$key = $this->iterator->key();
if ($key === null) {
return;
}
$this->items[$key] = $this->iterator->current();
}
/**
* Wraps the Traversable with a Generator.
*
* @param Traversable $traversable
* @return Generator
*/
private function wrapTraversable(Traversable $traversable)
{
foreach ($traversable as $key => $value) {
yield $key => $value;
$this->iteratorAdvanced = true;
}
$this->iteratorExhausted = true;
}
}