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<?php
namespace Jaeger\Util;
use Psr\Cache\CacheItemInterface;
use Psr\Cache\CacheItemPoolInterface;
class RateLimiter
{
/**
* @var CacheItemPoolInterface
*/
private $cache;
/**
* @var CacheItemInterface
*/
private $balance;
/**
* @var CacheItemInterface
*/
private $lastTick;
/**
* @var float
*/
private $creditsPerNanosecond = 0;
/**
* @var float
*/
private $maxBalance = 0;
/**
* RateLimiter constructor.
*
* @param CacheItemPoolInterface $cache
* @param string $currentBalanceKey key of current balance value in $cache
* @param string $lastTickKey key of last tick value in $cache
* @throws \Psr\Cache\InvalidArgumentException
*/
public function __construct(
CacheItemPoolInterface $cache,
string $currentBalanceKey,
string $lastTickKey
) {
$this->cache = $cache;
$this->balance = $this->cache->getItem($currentBalanceKey);
$this->lastTick = $this->cache->getItem($lastTickKey);
}
/**
* @param $itemCost
* @return bool
*/
public function checkCredit($itemCost)
{
if (!$this->creditsPerNanosecond) {
return false;
}
list($lastTick, $balance) = $this->getState();
if (!$lastTick) {
$this->saveState(hrtime(true), 0);
return true;
}
$currentTick = hrtime(true);
$elapsedTime = $currentTick - $lastTick;
$balance += $elapsedTime * $this->creditsPerNanosecond;
if ($balance > $this->maxBalance) {
$balance = $this->maxBalance;
}
$result = false;
if ($balance >= $itemCost) {
$balance -= $itemCost;
$result = true;
}
$this->saveState($currentTick, $balance);
return $result;
}
/**
* Initializes limiter costs and boundaries
*
* @param float $creditsPerNanosecond
* @param float $maxBalance
*/
public function initialize(float $creditsPerNanosecond, float $maxBalance)
{
$this->creditsPerNanosecond = $creditsPerNanosecond;
$this->maxBalance = $maxBalance;
}
/**
* Method loads last tick and current balance from cache
*
* @return array [$lastTick, $balance]
*/
private function getState() : array
{
return [
$this->lastTick->get(),
$this->balance->get()
];
}
/**
* Method saves last tick and current balance into cache
*
* @param integer $lastTick
* @param float $balance
*/
private function saveState($lastTick, $balance)
{
$this->lastTick->set($lastTick);
$this->balance->set($balance);
$this->cache->saveDeferred($this->lastTick);
$this->cache->saveDeferred($this->balance);
$this->cache->commit();
}
}
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