class MemcachedStore

class MemcachedStore implements PersistingStoreInterface {
    use ExpiringStoreTrait;
    private bool $useExtendedReturn;
    public static function isSupported() : bool {
        return \extension_loaded('memcached');
    }
    
    /**
     * @param int $initialTtl the expiration delay of locks in seconds
     */
    public function __construct(\Memcached $memcached, int $initialTtl = 300) {
        if (!static::isSupported()) {
            throw new InvalidArgumentException('Memcached extension is required.');
        }
        if ($initialTtl < 1) {
            throw new InvalidArgumentException(\sprintf('"%s()" expects a strictly positive TTL. Got %d.', __METHOD__, $initialTtl));
        }
    }
    public function save(Key $key) : void {
        $token = $this->getUniqueToken($key);
        $key->reduceLifetime($this->initialTtl);
        if (!$this->memcached
            ->add((string) $key, $token, (int) ceil($this->initialTtl))) {
            // the lock is already acquired. It could be us. Let's try to put off.
            $this->putOffExpiration($key, $this->initialTtl);
        }
        $this->checkNotExpired($key);
    }
    public function putOffExpiration(Key $key, float $ttl) : void {
        if ($ttl < 1) {
            throw new InvalidTtlException(\sprintf('"%s()" expects a TTL greater or equals to 1 second. Got %s.', __METHOD__, $ttl));
        }
        // Interface defines a float value but Store required an integer.
        $ttl = (int) ceil($ttl);
        $token = $this->getUniqueToken($key);
        [
            $value,
            $cas,
        ] = $this->getValueAndCas($key);
        $key->reduceLifetime($ttl);
        // Could happens when we ask a putOff after a timeout but in luck nobody steal the lock
        if (\Memcached::RES_NOTFOUND === $this->memcached
            ->getResultCode()) {
            if ($this->memcached
                ->add((string) $key, $token, $ttl)) {
                return;
            }
            // no luck, with concurrency, someone else acquire the lock
            throw new LockConflictedException();
        }
        // Someone else steal the lock
        if ($value !== $token) {
            throw new LockConflictedException();
        }
        if (!$this->memcached
            ->cas($cas, (string) $key, $token, $ttl)) {
            throw new LockConflictedException();
        }
        $this->checkNotExpired($key);
    }
    public function delete(Key $key) : void {
        $token = $this->getUniqueToken($key);
        [
            $value,
            $cas,
        ] = $this->getValueAndCas($key);
        if ($value !== $token) {
            // we are not the owner of the lock. Nothing to do.
            return;
        }
        // To avoid concurrency in deletion, the trick is to extends the TTL then deleting the key
        if (!$this->memcached
            ->cas($cas, (string) $key, $token, 2)) {
            // Someone steal our lock. It does not belongs to us anymore. Nothing to do.
            return;
        }
        // Now, we are the owner of the lock for 2 more seconds, we can delete it.
        $this->memcached
            ->delete((string) $key);
    }
    public function exists(Key $key) : bool {
        return $this->memcached
            ->get((string) $key) === $this->getUniqueToken($key);
    }
    private function getUniqueToken(Key $key) : string {
        if (!$key->hasState(__CLASS__)) {
            $token = base64_encode(random_bytes(32));
            $key->setState(__CLASS__, $token);
        }
        return $key->getState(__CLASS__);
    }
    private function getValueAndCas(Key $key) : array {
        if ($this->useExtendedReturn ??= version_compare(phpversion('memcached'), '2.9.9', '>')) {
            $extendedReturn = $this->memcached
                ->get((string) $key, null, \Memcached::GET_EXTENDED);
            if (\Memcached::GET_ERROR_RETURN_VALUE === $extendedReturn) {
                return [
                    $extendedReturn,
                    0.0,
                ];
            }
            return [
                $extendedReturn['value'],
                $extendedReturn['cas'],
            ];
        }
        $cas = 0.0;
        $value = $this->memcached
            ->get((string) $key, null, $cas);
        return [
            $value,
            $cas,
        ];
    }

}