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<?php
/*
* Copyright 2017-present 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
*
* https://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 Iterator;
use IteratorIterator;
use ReturnTypeWillChange;
use Traversable;
use function count;
use function current;
use function next;
use function reset;
/**
* 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 const FIELD_KEY = 0;
private const FIELD_VALUE = 1;
/** @var array */
private $items = [];
/** @var Iterator */
private $iterator;
/** @var boolean */
private $iteratorAdvanced = false;
/** @var boolean */
private $iteratorExhausted = false;
/**
* Initialize the iterator and stores the first item in the cache. This
* effectively rewinds the Traversable and the wrapping IteratorIterator.
* 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 = $traversable instanceof Iterator ? $traversable : new IteratorIterator($traversable);
$this->iterator->rewind();
$this->storeCurrentItem();
}
/**
* @see https://php.net/countable.count
*/
public function count(): int
{
$this->exhaustIterator();
return count($this->items);
}
/**
* @see https://php.net/iterator.current
* @return mixed
*/
#[ReturnTypeWillChange]
public function current()
{
$currentItem = current($this->items);
return $currentItem !== false ? $currentItem[self::FIELD_VALUE] : false;
}
/**
* @see https://php.net/iterator.key
* @return mixed
*/
#[ReturnTypeWillChange]
public function key()
{
$currentItem = current($this->items);
return $currentItem !== false ? $currentItem[self::FIELD_KEY] : null;
}
/**
* @see https://php.net/iterator.next
*/
public function next(): void
{
if (! $this->iteratorExhausted) {
$this->iteratorAdvanced = true;
$this->iterator->next();
$this->storeCurrentItem();
$this->iteratorExhausted = ! $this->iterator->valid();
}
next($this->items);
}
/**
* @see https://php.net/iterator.rewind
*/
public function rewind(): void
{
/* 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 https://php.net/iterator.valid
*/
public function valid(): bool
{
return $this->key() !== null;
}
/**
* Ensures that the inner iterator is fully consumed and cached.
*/
private function exhaustIterator(): void
{
while (! $this->iteratorExhausted) {
$this->next();
}
}
/**
* Stores the current item in the cache.
*/
private function storeCurrentItem(): void
{
if (! $this->iterator->valid()) {
return;
}
// Storing a new item in the internal cache
$this->items[] = [
self::FIELD_KEY => $this->iterator->key(),
self::FIELD_VALUE => $this->iterator->current(),
];
}
}
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