class Response

class Response {
    public const HTTP_CONTINUE = 100;
    public const HTTP_SWITCHING_PROTOCOLS = 101;
    public const HTTP_PROCESSING = 102;
    // RFC2518
    public const HTTP_EARLY_HINTS = 103;
    // RFC8297
    public const HTTP_OK = 200;
    public const HTTP_CREATED = 201;
    public const HTTP_ACCEPTED = 202;
    public const HTTP_NON_AUTHORITATIVE_INFORMATION = 203;
    public const HTTP_NO_CONTENT = 204;
    public const HTTP_RESET_CONTENT = 205;
    public const HTTP_PARTIAL_CONTENT = 206;
    public const HTTP_MULTI_STATUS = 207;
    // RFC4918
    public const HTTP_ALREADY_REPORTED = 208;
    // RFC5842
    public const HTTP_IM_USED = 226;
    // RFC3229
    public const HTTP_MULTIPLE_CHOICES = 300;
    public const HTTP_MOVED_PERMANENTLY = 301;
    public const HTTP_FOUND = 302;
    public const HTTP_SEE_OTHER = 303;
    public const HTTP_NOT_MODIFIED = 304;
    public const HTTP_USE_PROXY = 305;
    public const HTTP_RESERVED = 306;
    public const HTTP_TEMPORARY_REDIRECT = 307;
    public const HTTP_PERMANENTLY_REDIRECT = 308;
    // RFC7238
    public const HTTP_BAD_REQUEST = 400;
    public const HTTP_UNAUTHORIZED = 401;
    public const HTTP_PAYMENT_REQUIRED = 402;
    public const HTTP_FORBIDDEN = 403;
    public const HTTP_NOT_FOUND = 404;
    public const HTTP_METHOD_NOT_ALLOWED = 405;
    public const HTTP_NOT_ACCEPTABLE = 406;
    public const HTTP_PROXY_AUTHENTICATION_REQUIRED = 407;
    public const HTTP_REQUEST_TIMEOUT = 408;
    public const HTTP_CONFLICT = 409;
    public const HTTP_GONE = 410;
    public const HTTP_LENGTH_REQUIRED = 411;
    public const HTTP_PRECONDITION_FAILED = 412;
    public const HTTP_REQUEST_ENTITY_TOO_LARGE = 413;
    public const HTTP_REQUEST_URI_TOO_LONG = 414;
    public const HTTP_UNSUPPORTED_MEDIA_TYPE = 415;
    public const HTTP_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
    public const HTTP_EXPECTATION_FAILED = 417;
    public const HTTP_I_AM_A_TEAPOT = 418;
    // RFC2324
    public const HTTP_MISDIRECTED_REQUEST = 421;
    // RFC7540
    public const HTTP_UNPROCESSABLE_ENTITY = 422;
    // RFC4918
    public const HTTP_LOCKED = 423;
    // RFC4918
    public const HTTP_FAILED_DEPENDENCY = 424;
    // RFC4918
    public const HTTP_TOO_EARLY = 425;
    // RFC-ietf-httpbis-replay-04
    public const HTTP_UPGRADE_REQUIRED = 426;
    // RFC2817
    public const HTTP_PRECONDITION_REQUIRED = 428;
    // RFC6585
    public const HTTP_TOO_MANY_REQUESTS = 429;
    // RFC6585
    public const HTTP_REQUEST_HEADER_FIELDS_TOO_LARGE = 431;
    // RFC6585
    public const HTTP_UNAVAILABLE_FOR_LEGAL_REASONS = 451;
    // RFC7725
    public const HTTP_INTERNAL_SERVER_ERROR = 500;
    public const HTTP_NOT_IMPLEMENTED = 501;
    public const HTTP_BAD_GATEWAY = 502;
    public const HTTP_SERVICE_UNAVAILABLE = 503;
    public const HTTP_GATEWAY_TIMEOUT = 504;
    public const HTTP_VERSION_NOT_SUPPORTED = 505;
    public const HTTP_VARIANT_ALSO_NEGOTIATES_EXPERIMENTAL = 506;
    // RFC2295
    public const HTTP_INSUFFICIENT_STORAGE = 507;
    // RFC4918
    public const HTTP_LOOP_DETECTED = 508;
    // RFC5842
    public const HTTP_NOT_EXTENDED = 510;
    // RFC2774
    public const HTTP_NETWORK_AUTHENTICATION_REQUIRED = 511;
    // RFC6585
    
    /**
     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
     */
    private const HTTP_RESPONSE_CACHE_CONTROL_DIRECTIVES = [
        'must_revalidate' => false,
        'no_cache' => false,
        'no_store' => false,
        'no_transform' => false,
        'public' => false,
        'private' => false,
        'proxy_revalidate' => false,
        'max_age' => true,
        's_maxage' => true,
        'stale_if_error' => true,
        // RFC5861
'stale_while_revalidate' => true,
        // RFC5861
'immutable' => false,
        'last_modified' => true,
        'etag' => true,
    ];
    public ResponseHeaderBag $headers;
    protected string $content;
    protected string $version;
    protected int $statusCode;
    protected string $statusText;
    protected ?string $charset = null;
    
    /**
     * Status codes translation table.
     *
     * The list of codes is complete according to the
     * {@link https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml Hypertext Transfer Protocol (HTTP) Status Code Registry}
     * (last updated 2021-10-01).
     *
     * Unless otherwise noted, the status code is defined in RFC2616.
     */
    public static array $statusTexts = [
        100 => 'Continue',
        101 => 'Switching Protocols',
        102 => 'Processing',
        // RFC2518
103 => 'Early Hints',
        200 => 'OK',
        201 => 'Created',
        202 => 'Accepted',
        203 => 'Non-Authoritative Information',
        204 => 'No Content',
        205 => 'Reset Content',
        206 => 'Partial Content',
        207 => 'Multi-Status',
        // RFC4918
208 => 'Already Reported',
        // RFC5842
226 => 'IM Used',
        // RFC3229
300 => 'Multiple Choices',
        301 => 'Moved Permanently',
        302 => 'Found',
        303 => 'See Other',
        304 => 'Not Modified',
        305 => 'Use Proxy',
        307 => 'Temporary Redirect',
        308 => 'Permanent Redirect',
        // RFC7238
400 => 'Bad Request',
        401 => 'Unauthorized',
        402 => 'Payment Required',
        403 => 'Forbidden',
        404 => 'Not Found',
        405 => 'Method Not Allowed',
        406 => 'Not Acceptable',
        407 => 'Proxy Authentication Required',
        408 => 'Request Timeout',
        409 => 'Conflict',
        410 => 'Gone',
        411 => 'Length Required',
        412 => 'Precondition Failed',
        413 => 'Content Too Large',
        // RFC-ietf-httpbis-semantics
414 => 'URI Too Long',
        415 => 'Unsupported Media Type',
        416 => 'Range Not Satisfiable',
        417 => 'Expectation Failed',
        418 => 'I\'m a teapot',
        // RFC2324
421 => 'Misdirected Request',
        // RFC7540
422 => 'Unprocessable Content',
        // RFC-ietf-httpbis-semantics
423 => 'Locked',
        // RFC4918
424 => 'Failed Dependency',
        // RFC4918
425 => 'Too Early',
        // RFC-ietf-httpbis-replay-04
426 => 'Upgrade Required',
        // RFC2817
428 => 'Precondition Required',
        // RFC6585
429 => 'Too Many Requests',
        // RFC6585
431 => 'Request Header Fields Too Large',
        // RFC6585
451 => 'Unavailable For Legal Reasons',
        // RFC7725
500 => 'Internal Server Error',
        501 => 'Not Implemented',
        502 => 'Bad Gateway',
        503 => 'Service Unavailable',
        504 => 'Gateway Timeout',
        505 => 'HTTP Version Not Supported',
        506 => 'Variant Also Negotiates',
        // RFC2295
507 => 'Insufficient Storage',
        // RFC4918
508 => 'Loop Detected',
        // RFC5842
510 => 'Not Extended',
        // RFC2774
511 => 'Network Authentication Required',
    ];
    
    /**
     * Tracks headers already sent in informational responses.
     */
    private array $sentHeaders;
    
    /**
     * @param int $status The HTTP status code (200 "OK" by default)
     *
     * @throws \InvalidArgumentException When the HTTP status code is not valid
     */
    public function __construct(?string $content = '', int $status = 200, array $headers = []) {
        $this->headers = new ResponseHeaderBag($headers);
        $this->setContent($content);
        $this->setStatusCode($status);
        $this->setProtocolVersion('1.0');
    }
    
    /**
     * Returns the Response as an HTTP string.
     *
     * The string representation of the Response is the same as the
     * one that will be sent to the client only if the prepare() method
     * has been called before.
     *
     * @see prepare()
     */
    public function __toString() : string {
        return \sprintf('HTTP/%s %s %s', $this->version, $this->statusCode, $this->statusText) . "\r\n" . $this->headers . "\r\n" . $this->getContent();
    }
    
    /**
     * Clones the current Response instance.
     */
    public function __clone() {
        $this->headers = clone $this->headers;
    }
    
    /**
     * Prepares the Response before it is sent to the client.
     *
     * This method tweaks the Response to ensure that it is
     * compliant with RFC 2616. Most of the changes are based on
     * the Request that is "associated" with this Response.
     *
     * @return $this
     */
    public function prepare(Request $request) : static {
        $headers = $this->headers;
        if ($this->isInformational() || $this->isEmpty()) {
            $this->setContent(null);
            $headers->remove('Content-Type');
            $headers->remove('Content-Length');
            // prevent PHP from sending the Content-Type header based on default_mimetype
            ini_set('default_mimetype', '');
        }
        else {
            // Content-type based on the Request
            if (!$headers->has('Content-Type')) {
                $format = $request->getRequestFormat(null);
                if (null !== $format && ($mimeType = $request->getMimeType($format))) {
                    $headers->set('Content-Type', $mimeType);
                }
            }
            // Fix Content-Type
            $charset = $this->charset ?: 'UTF-8';
            if (!$headers->has('Content-Type')) {
                $headers->set('Content-Type', 'text/html; charset=' . $charset);
            }
            elseif (0 === stripos($headers->get('Content-Type') ?? '', 'text/') && false === stripos($headers->get('Content-Type') ?? '', 'charset')) {
                // add the charset
                $headers->set('Content-Type', $headers->get('Content-Type') . '; charset=' . $charset);
            }
            // Fix Content-Length
            if ($headers->has('Transfer-Encoding')) {
                $headers->remove('Content-Length');
            }
            if ($request->isMethod('HEAD')) {
                // cf. RFC2616 14.13
                $length = $headers->get('Content-Length');
                $this->setContent(null);
                if ($length) {
                    $headers->set('Content-Length', $length);
                }
            }
        }
        // Fix protocol
        if ('HTTP/1.0' != $request->server
            ->get('SERVER_PROTOCOL')) {
            $this->setProtocolVersion('1.1');
        }
        // Check if we need to send extra expire info headers
        if ('1.0' == $this->getProtocolVersion() && str_contains($headers->get('Cache-Control', ''), 'no-cache')) {
            $headers->set('pragma', 'no-cache');
            $headers->set('expires', -1);
        }
        $this->ensureIEOverSSLCompatibility($request);
        if ($request->isSecure()) {
            foreach ($headers->getCookies() as $cookie) {
                $cookie->setSecureDefault(true);
            }
        }
        return $this;
    }
    
    /**
     * Sends HTTP headers.
     *
     * @param positive-int|null $statusCode The status code to use, override the statusCode property if set and not null
     *
     * @return $this
     */
    public function sendHeaders(?int $statusCode = null) : static {
        // headers have already been sent by the developer
        if (headers_sent()) {
            return $this;
        }
        $informationalResponse = $statusCode >= 100 && $statusCode < 200;
        if ($informationalResponse && !\function_exists('headers_send')) {
            // skip informational responses if not supported by the SAPI
            return $this;
        }
        // headers
        foreach ($this->headers
            ->allPreserveCaseWithoutCookies() as $name => $values) {
            // As recommended by RFC 8297, PHP automatically copies headers from previous 103 responses, we need to deal with that if headers changed
            $previousValues = $this->sentHeaders[$name] ?? null;
            if ($previousValues === $values) {
                // Header already sent in a previous response, it will be automatically copied in this response by PHP
                continue;
            }
            $replace = 0 === strcasecmp($name, 'Content-Type');
            if (null !== $previousValues && array_diff($previousValues, $values)) {
                header_remove($name);
                $previousValues = null;
            }
            $newValues = null === $previousValues ? $values : array_diff($values, $previousValues);
            foreach ($newValues as $value) {
                header($name . ': ' . $value, $replace, $this->statusCode);
            }
            if ($informationalResponse) {
                $this->sentHeaders[$name] = $values;
            }
        }
        // cookies
        foreach ($this->headers
            ->getCookies() as $cookie) {
            header('Set-Cookie: ' . $cookie, false, $this->statusCode);
        }
        if ($informationalResponse) {
            headers_send($statusCode);
            return $this;
        }
        $statusCode ??= $this->statusCode;
        // status
        header(\sprintf('HTTP/%s %s %s', $this->version, $statusCode, $this->statusText), true, $statusCode);
        return $this;
    }
    
    /**
     * Sends content for the current web response.
     *
     * @return $this
     */
    public function sendContent() : static {
        echo $this->content;
        return $this;
    }
    
    /**
     * Sends HTTP headers and content.
     *
     * @param bool $flush Whether output buffers should be flushed
     *
     * @return $this
     */
    public function send(bool $flush = true) : static {
        $this->sendHeaders();
        $this->sendContent();
        if (!$flush) {
            return $this;
        }
        if (\function_exists('fastcgi_finish_request')) {
            fastcgi_finish_request();
        }
        elseif (\function_exists('litespeed_finish_request')) {
            litespeed_finish_request();
        }
        elseif (!\in_array(\PHP_SAPI, [
            'cli',
            'phpdbg',
            'embed',
        ], true)) {
            static::closeOutputBuffers(0, true);
            flush();
        }
        return $this;
    }
    
    /**
     * Sets the response content.
     *
     * @return $this
     */
    public function setContent(?string $content) : static {
        $this->content = $content ?? '';
        return $this;
    }
    
    /**
     * Gets the current response content.
     */
    public function getContent() : string|false {
        return $this->content;
    }
    
    /**
     * Sets the HTTP protocol version (1.0 or 1.1).
     *
     * @return $this
     *
     * @final
     */
    public function setProtocolVersion(string $version) : static {
        $this->version = $version;
        return $this;
    }
    
    /**
     * Gets the HTTP protocol version.
     *
     * @final
     */
    public function getProtocolVersion() : string {
        return $this->version;
    }
    
    /**
     * Sets the response status code.
     *
     * If the status text is null it will be automatically populated for the known
     * status codes and left empty otherwise.
     *
     * @return $this
     *
     * @throws \InvalidArgumentException When the HTTP status code is not valid
     *
     * @final
     */
    public function setStatusCode(int $code, ?string $text = null) : static {
        $this->statusCode = $code;
        if ($this->isInvalid()) {
            throw new \InvalidArgumentException(\sprintf('The HTTP status code "%s" is not valid.', $code));
        }
        if (null === $text) {
            $this->statusText = self::$statusTexts[$code] ?? 'unknown status';
            return $this;
        }
        $this->statusText = $text;
        return $this;
    }
    
    /**
     * Retrieves the status code for the current web response.
     *
     * @final
     */
    public function getStatusCode() : int {
        return $this->statusCode;
    }
    
    /**
     * Sets the response charset.
     *
     * @return $this
     *
     * @final
     */
    public function setCharset(string $charset) : static {
        $this->charset = $charset;
        return $this;
    }
    
    /**
     * Retrieves the response charset.
     *
     * @final
     */
    public function getCharset() : ?string {
        return $this->charset;
    }
    
    /**
     * Returns true if the response may safely be kept in a shared (surrogate) cache.
     *
     * Responses marked "private" with an explicit Cache-Control directive are
     * considered uncacheable.
     *
     * Responses with neither a freshness lifetime (Expires, max-age) nor cache
     * validator (Last-Modified, ETag) are considered uncacheable because there is
     * no way to tell when or how to remove them from the cache.
     *
     * Note that RFC 7231 and RFC 7234 possibly allow for a more permissive implementation,
     * for example "status codes that are defined as cacheable by default [...]
     * can be reused by a cache with heuristic expiration unless otherwise indicated"
     * (https://tools.ietf.org/html/rfc7231#section-6.1)
     *
     * @final
     */
    public function isCacheable() : bool {
        if (!\in_array($this->statusCode, [
            200,
            203,
            300,
            301,
            302,
            404,
            410,
        ])) {
            return false;
        }
        if ($this->headers
            ->hasCacheControlDirective('no-store') || $this->headers
            ->getCacheControlDirective('private')) {
            return false;
        }
        return $this->isValidateable() || $this->isFresh();
    }
    
    /**
     * Returns true if the response is "fresh".
     *
     * Fresh responses may be served from cache without any interaction with the
     * origin. A response is considered fresh when it includes a Cache-Control/max-age
     * indicator or Expires header and the calculated age is less than the freshness lifetime.
     *
     * @final
     */
    public function isFresh() : bool {
        return $this->getTtl() > 0;
    }
    
    /**
     * Returns true if the response includes headers that can be used to validate
     * the response with the origin server using a conditional GET request.
     *
     * @final
     */
    public function isValidateable() : bool {
        return $this->headers
            ->has('Last-Modified') || $this->headers
            ->has('ETag');
    }
    
    /**
     * Marks the response as "private".
     *
     * It makes the response ineligible for serving other clients.
     *
     * @return $this
     *
     * @final
     */
    public function setPrivate() : static {
        $this->headers
            ->removeCacheControlDirective('public');
        $this->headers
            ->addCacheControlDirective('private');
        return $this;
    }
    
    /**
     * Marks the response as "public".
     *
     * It makes the response eligible for serving other clients.
     *
     * @return $this
     *
     * @final
     */
    public function setPublic() : static {
        $this->headers
            ->addCacheControlDirective('public');
        $this->headers
            ->removeCacheControlDirective('private');
        return $this;
    }
    
    /**
     * Marks the response as "immutable".
     *
     * @return $this
     *
     * @final
     */
    public function setImmutable(bool $immutable = true) : static {
        if ($immutable) {
            $this->headers
                ->addCacheControlDirective('immutable');
        }
        else {
            $this->headers
                ->removeCacheControlDirective('immutable');
        }
        return $this;
    }
    
    /**
     * Returns true if the response is marked as "immutable".
     *
     * @final
     */
    public function isImmutable() : bool {
        return $this->headers
            ->hasCacheControlDirective('immutable');
    }
    
    /**
     * Returns true if the response must be revalidated by shared caches once it has become stale.
     *
     * This method indicates that the response must not be served stale by a
     * cache in any circumstance without first revalidating with the origin.
     * When present, the TTL of the response should not be overridden to be
     * greater than the value provided by the origin.
     *
     * @final
     */
    public function mustRevalidate() : bool {
        return $this->headers
            ->hasCacheControlDirective('must-revalidate') || $this->headers
            ->hasCacheControlDirective('proxy-revalidate');
    }
    
    /**
     * Returns the Date header as a DateTime instance.
     *
     * @throws \RuntimeException When the header is not parseable
     *
     * @final
     */
    public function getDate() : ?\DateTimeImmutable {
        return $this->headers
            ->getDate('Date');
    }
    
    /**
     * Sets the Date header.
     *
     * @return $this
     *
     * @final
     */
    public function setDate(\DateTimeInterface $date) : static {
        $date = \DateTimeImmutable::createFromInterface($date);
        $date = $date->setTimezone(new \DateTimeZone('UTC'));
        $this->headers
            ->set('Date', $date->format('D, d M Y H:i:s') . ' GMT');
        return $this;
    }
    
    /**
     * Returns the age of the response in seconds.
     *
     * @final
     */
    public function getAge() : int {
        if (null !== ($age = $this->headers
            ->get('Age'))) {
            return (int) $age;
        }
        return max(time() - (int) $this->getDate()
            ->format('U'), 0);
    }
    
    /**
     * Marks the response stale by setting the Age header to be equal to the maximum age of the response.
     *
     * @return $this
     */
    public function expire() : static {
        if ($this->isFresh()) {
            $this->headers
                ->set('Age', $this->getMaxAge());
            $this->headers
                ->remove('Expires');
        }
        return $this;
    }
    
    /**
     * Returns the value of the Expires header as a DateTime instance.
     *
     * @final
     */
    public function getExpires() : ?\DateTimeImmutable {
        try {
            return $this->headers
                ->getDate('Expires');
        } catch (\RuntimeException) {
            // according to RFC 2616 invalid date formats (e.g. "0" and "-1") must be treated as in the past
            return \DateTimeImmutable::createFromFormat('U', time() - 172800);
        }
    }
    
    /**
     * Sets the Expires HTTP header with a DateTime instance.
     *
     * Passing null as value will remove the header.
     *
     * @return $this
     *
     * @final
     */
    public function setExpires(?\DateTimeInterface $date) : static {
        if (null === $date) {
            $this->headers
                ->remove('Expires');
            return $this;
        }
        $date = \DateTimeImmutable::createFromInterface($date);
        $date = $date->setTimezone(new \DateTimeZone('UTC'));
        $this->headers
            ->set('Expires', $date->format('D, d M Y H:i:s') . ' GMT');
        return $this;
    }
    
    /**
     * Returns the number of seconds after the time specified in the response's Date
     * header when the response should no longer be considered fresh.
     *
     * First, it checks for a s-maxage directive, then a max-age directive, and then it falls
     * back on an expires header. It returns null when no maximum age can be established.
     *
     * @final
     */
    public function getMaxAge() : ?int {
        if ($this->headers
            ->hasCacheControlDirective('s-maxage')) {
            return (int) $this->headers
                ->getCacheControlDirective('s-maxage');
        }
        if ($this->headers
            ->hasCacheControlDirective('max-age')) {
            return (int) $this->headers
                ->getCacheControlDirective('max-age');
        }
        if (null !== ($expires = $this->getExpires())) {
            $maxAge = (int) $expires->format('U') - (int) $this->getDate()
                ->format('U');
            return max($maxAge, 0);
        }
        return null;
    }
    
    /**
     * Sets the number of seconds after which the response should no longer be considered fresh.
     *
     * This method sets the Cache-Control max-age directive.
     *
     * @return $this
     *
     * @final
     */
    public function setMaxAge(int $value) : static {
        $this->headers
            ->addCacheControlDirective('max-age', $value);
        return $this;
    }
    
    /**
     * Sets the number of seconds after which the response should no longer be returned by shared caches when backend is down.
     *
     * This method sets the Cache-Control stale-if-error directive.
     *
     * @return $this
     *
     * @final
     */
    public function setStaleIfError(int $value) : static {
        $this->headers
            ->addCacheControlDirective('stale-if-error', $value);
        return $this;
    }
    
    /**
     * Sets the number of seconds after which the response should no longer return stale content by shared caches.
     *
     * This method sets the Cache-Control stale-while-revalidate directive.
     *
     * @return $this
     *
     * @final
     */
    public function setStaleWhileRevalidate(int $value) : static {
        $this->headers
            ->addCacheControlDirective('stale-while-revalidate', $value);
        return $this;
    }
    
    /**
     * Sets the number of seconds after which the response should no longer be considered fresh by shared caches.
     *
     * This method sets the Cache-Control s-maxage directive.
     *
     * @return $this
     *
     * @final
     */
    public function setSharedMaxAge(int $value) : static {
        $this->setPublic();
        $this->headers
            ->addCacheControlDirective('s-maxage', $value);
        return $this;
    }
    
    /**
     * Returns the response's time-to-live in seconds.
     *
     * It returns null when no freshness information is present in the response.
     *
     * When the response's TTL is 0, the response may not be served from cache without first
     * revalidating with the origin.
     *
     * @final
     */
    public function getTtl() : ?int {
        $maxAge = $this->getMaxAge();
        return null !== $maxAge ? max($maxAge - $this->getAge(), 0) : null;
    }
    
    /**
     * Sets the response's time-to-live for shared caches in seconds.
     *
     * This method adjusts the Cache-Control/s-maxage directive.
     *
     * @return $this
     *
     * @final
     */
    public function setTtl(int $seconds) : static {
        $this->setSharedMaxAge($this->getAge() + $seconds);
        return $this;
    }
    
    /**
     * Sets the response's time-to-live for private/client caches in seconds.
     *
     * This method adjusts the Cache-Control/max-age directive.
     *
     * @return $this
     *
     * @final
     */
    public function setClientTtl(int $seconds) : static {
        $this->setMaxAge($this->getAge() + $seconds);
        return $this;
    }
    
    /**
     * Returns the Last-Modified HTTP header as a DateTime instance.
     *
     * @throws \RuntimeException When the HTTP header is not parseable
     *
     * @final
     */
    public function getLastModified() : ?\DateTimeImmutable {
        return $this->headers
            ->getDate('Last-Modified');
    }
    
    /**
     * Sets the Last-Modified HTTP header with a DateTime instance.
     *
     * Passing null as value will remove the header.
     *
     * @return $this
     *
     * @final
     */
    public function setLastModified(?\DateTimeInterface $date) : static {
        if (null === $date) {
            $this->headers
                ->remove('Last-Modified');
            return $this;
        }
        $date = \DateTimeImmutable::createFromInterface($date);
        $date = $date->setTimezone(new \DateTimeZone('UTC'));
        $this->headers
            ->set('Last-Modified', $date->format('D, d M Y H:i:s') . ' GMT');
        return $this;
    }
    
    /**
     * Returns the literal value of the ETag HTTP header.
     *
     * @final
     */
    public function getEtag() : ?string {
        return $this->headers
            ->get('ETag');
    }
    
    /**
     * Sets the ETag value.
     *
     * @param string|null $etag The ETag unique identifier or null to remove the header
     * @param bool        $weak Whether you want a weak ETag or not
     *
     * @return $this
     *
     * @final
     */
    public function setEtag(?string $etag, bool $weak = false) : static {
        if (null === $etag) {
            $this->headers
                ->remove('Etag');
        }
        else {
            if (!str_starts_with($etag, '"')) {
                $etag = '"' . $etag . '"';
            }
            $this->headers
                ->set('ETag', (true === $weak ? 'W/' : '') . $etag);
        }
        return $this;
    }
    
    /**
     * Sets the response's cache headers (validation and/or expiration).
     *
     * Available options are: must_revalidate, no_cache, no_store, no_transform, public, private, proxy_revalidate, max_age, s_maxage, immutable, last_modified and etag.
     *
     * @return $this
     *
     * @throws \InvalidArgumentException
     *
     * @final
     */
    public function setCache(array $options) : static {
        if ($diff = array_diff(array_keys($options), array_keys(self::HTTP_RESPONSE_CACHE_CONTROL_DIRECTIVES))) {
            throw new \InvalidArgumentException(\sprintf('Response does not support the following options: "%s".', implode('", "', $diff)));
        }
        if (isset($options['etag'])) {
            $this->setEtag($options['etag']);
        }
        if (isset($options['last_modified'])) {
            $this->setLastModified($options['last_modified']);
        }
        if (isset($options['max_age'])) {
            $this->setMaxAge($options['max_age']);
        }
        if (isset($options['s_maxage'])) {
            $this->setSharedMaxAge($options['s_maxage']);
        }
        if (isset($options['stale_while_revalidate'])) {
            $this->setStaleWhileRevalidate($options['stale_while_revalidate']);
        }
        if (isset($options['stale_if_error'])) {
            $this->setStaleIfError($options['stale_if_error']);
        }
        foreach (self::HTTP_RESPONSE_CACHE_CONTROL_DIRECTIVES as $directive => $hasValue) {
            if (!$hasValue && isset($options[$directive])) {
                if ($options[$directive]) {
                    $this->headers
                        ->addCacheControlDirective(str_replace('_', '-', $directive));
                }
                else {
                    $this->headers
                        ->removeCacheControlDirective(str_replace('_', '-', $directive));
                }
            }
        }
        if (isset($options['public'])) {
            if ($options['public']) {
                $this->setPublic();
            }
            else {
                $this->setPrivate();
            }
        }
        if (isset($options['private'])) {
            if ($options['private']) {
                $this->setPrivate();
            }
            else {
                $this->setPublic();
            }
        }
        return $this;
    }
    
    /**
     * Modifies the response so that it conforms to the rules defined for a 304 status code.
     *
     * This sets the status, removes the body, and discards any headers
     * that MUST NOT be included in 304 responses.
     *
     * @return $this
     *
     * @see https://tools.ietf.org/html/rfc2616#section-10.3.5
     *
     * @final
     */
    public function setNotModified() : static {
        $this->setStatusCode(304);
        $this->setContent(null);
        // remove headers that MUST NOT be included with 304 Not Modified responses
        foreach ([
            'Allow',
            'Content-Encoding',
            'Content-Language',
            'Content-Length',
            'Content-MD5',
            'Content-Type',
            'Last-Modified',
        ] as $header) {
            $this->headers
                ->remove($header);
        }
        return $this;
    }
    
    /**
     * Returns true if the response includes a Vary header.
     *
     * @final
     */
    public function hasVary() : bool {
        return null !== $this->headers
            ->get('Vary');
    }
    
    /**
     * Returns an array of header names given in the Vary header.
     *
     * @final
     */
    public function getVary() : array {
        if (!($vary = $this->headers
            ->all('Vary'))) {
            return [];
        }
        $ret = [];
        foreach ($vary as $item) {
            $ret[] = preg_split('/[\\s,]+/', $item);
        }
        return array_merge([], ...$ret);
    }
    
    /**
     * Sets the Vary header.
     *
     * @param bool $replace Whether to replace the actual value or not (true by default)
     *
     * @return $this
     *
     * @final
     */
    public function setVary(string|array $headers, bool $replace = true) : static {
        $this->headers
            ->set('Vary', $headers, $replace);
        return $this;
    }
    
    /**
     * Determines if the Response validators (ETag, Last-Modified) match
     * a conditional value specified in the Request.
     *
     * If the Response is not modified, it sets the status code to 304 and
     * removes the actual content by calling the setNotModified() method.
     *
     * @final
     */
    public function isNotModified(Request $request) : bool {
        if (!$request->isMethodCacheable()) {
            return false;
        }
        $notModified = false;
        $lastModified = $this->headers
            ->get('Last-Modified');
        $modifiedSince = $request->headers
            ->get('If-Modified-Since');
        if (($ifNoneMatchEtags = $request->getETags()) && null !== ($etag = $this->getEtag())) {
            if (0 == strncmp($etag, 'W/', 2)) {
                $etag = substr($etag, 2);
            }
            // Use weak comparison as per https://tools.ietf.org/html/rfc7232#section-3.2.
            foreach ($ifNoneMatchEtags as $ifNoneMatchEtag) {
                if (0 == strncmp($ifNoneMatchEtag, 'W/', 2)) {
                    $ifNoneMatchEtag = substr($ifNoneMatchEtag, 2);
                }
                if ($ifNoneMatchEtag === $etag || '*' === $ifNoneMatchEtag) {
                    $notModified = true;
                    break;
                }
            }
        }
        elseif ($modifiedSince && $lastModified) {
            $notModified = strtotime($modifiedSince) >= strtotime($lastModified);
        }
        if ($notModified) {
            $this->setNotModified();
        }
        return $notModified;
    }
    
    /**
     * Is response invalid?
     *
     * @see https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
     *
     * @final
     */
    public function isInvalid() : bool {
        return $this->statusCode < 100 || $this->statusCode >= 600;
    }
    
    /**
     * Is response informative?
     *
     * @final
     */
    public function isInformational() : bool {
        return $this->statusCode >= 100 && $this->statusCode < 200;
    }
    
    /**
     * Is response successful?
     *
     * @final
     */
    public function isSuccessful() : bool {
        return $this->statusCode >= 200 && $this->statusCode < 300;
    }
    
    /**
     * Is the response a redirect?
     *
     * @final
     */
    public function isRedirection() : bool {
        return $this->statusCode >= 300 && $this->statusCode < 400;
    }
    
    /**
     * Is there a client error?
     *
     * @final
     */
    public function isClientError() : bool {
        return $this->statusCode >= 400 && $this->statusCode < 500;
    }
    
    /**
     * Was there a server side error?
     *
     * @final
     */
    public function isServerError() : bool {
        return $this->statusCode >= 500 && $this->statusCode < 600;
    }
    
    /**
     * Is the response OK?
     *
     * @final
     */
    public function isOk() : bool {
        return 200 === $this->statusCode;
    }
    
    /**
     * Is the response forbidden?
     *
     * @final
     */
    public function isForbidden() : bool {
        return 403 === $this->statusCode;
    }
    
    /**
     * Is the response a not found error?
     *
     * @final
     */
    public function isNotFound() : bool {
        return 404 === $this->statusCode;
    }
    
    /**
     * Is the response a redirect of some form?
     *
     * @final
     */
    public function isRedirect(?string $location = null) : bool {
        return \in_array($this->statusCode, [
            201,
            301,
            302,
            303,
            307,
            308,
        ]) && (null === $location ?: $location == $this->headers
            ->get('Location'));
    }
    
    /**
     * Is the response empty?
     *
     * @final
     */
    public function isEmpty() : bool {
        return \in_array($this->statusCode, [
            204,
            304,
        ]);
    }
    
    /**
     * Cleans or flushes output buffers up to target level.
     *
     * Resulting level can be greater than target level if a non-removable buffer has been encountered.
     *
     * @final
     */
    public static function closeOutputBuffers(int $targetLevel, bool $flush) : void {
        $status = ob_get_status(true);
        $level = \count($status);
        $flags = \PHP_OUTPUT_HANDLER_REMOVABLE | ($flush ? \PHP_OUTPUT_HANDLER_FLUSHABLE : \PHP_OUTPUT_HANDLER_CLEANABLE);
        while ($level-- > $targetLevel && ($s = $status[$level]) && (!isset($s['del']) ? !isset($s['flags']) || ($s['flags'] & $flags) === $flags : $s['del'])) {
            if ($flush) {
                ob_end_flush();
            }
            else {
                ob_end_clean();
            }
        }
    }
    
    /**
     * Marks a response as safe according to RFC8674.
     *
     * @see https://tools.ietf.org/html/rfc8674
     */
    public function setContentSafe(bool $safe = true) : void {
        if ($safe) {
            $this->headers
                ->set('Preference-Applied', 'safe');
        }
        elseif ('safe' === $this->headers
            ->get('Preference-Applied')) {
            $this->headers
                ->remove('Preference-Applied');
        }
        $this->setVary('Prefer', false);
    }
    
    /**
     * Checks if we need to remove Cache-Control for SSL encrypted downloads when using IE < 9.
     *
     * @see http://support.microsoft.com/kb/323308
     *
     * @final
     */
    protected function ensureIEOverSSLCompatibility(Request $request) : void {
        if (false !== stripos($this->headers
            ->get('Content-Disposition') ?? '', 'attachment') && 1 == preg_match('/MSIE (.*?);/i', $request->server
            ->get('HTTP_USER_AGENT') ?? '', $match) && true === $request->isSecure()) {
            if ((int) preg_replace('/(MSIE )(.*?);/', '$2', $match[0]) < 9) {
                $this->headers
                    ->remove('Cache-Control');
            }
        }
    }

}