class FnStream

final class FnStream implements StreamInterface {
    private const SLOTS = [
        '__toString',
        'close',
        'detach',
        'rewind',
        'getSize',
        'tell',
        'eof',
        'isSeekable',
        'seek',
        'isWritable',
        'write',
        'isReadable',
        'read',
        'getContents',
        'getMetadata',
    ];
    
    /** @var array<string, callable> */
    private $methods;
    
    /**
     * @param array<string, callable> $methods Hash of method name to a callable.
     */
    public function __construct(array $methods) {
        $this->methods = $methods;
        // Create the functions on the class
        foreach ($methods as $name => $fn) {
            $this->{'_fn_' . $name} = $fn;
        }
    }
    
    /**
     * Lazily determine which methods are not implemented.
     *
     * @throws \BadMethodCallException
     */
    public function __get(string $name) : void {
        throw new \BadMethodCallException(str_replace('_fn_', '', $name) . '() is not implemented in the FnStream');
    }
    
    /**
     * The close method is called on the underlying stream only if possible.
     */
    public function __destruct() {
        if (isset($this->_fn_close)) {
            ($this->_fn_close)();
        }
    }
    
    /**
     * An unserialize would allow the __destruct to run when the unserialized value goes out of scope.
     *
     * @throws \LogicException
     */
    public function __wakeup() : void {
        throw new \LogicException('FnStream should never be unserialized');
    }
    
    /**
     * Adds custom functionality to an underlying stream by intercepting
     * specific method calls.
     *
     * @param StreamInterface         $stream  Stream to decorate
     * @param array<string, callable> $methods Hash of method name to a closure
     *
     * @return FnStream
     */
    public static function decorate(StreamInterface $stream, array $methods) {
        // If any of the required methods were not provided, then simply
        // proxy to the decorated stream.
        foreach (array_diff(self::SLOTS, array_keys($methods)) as $diff) {
            
            /** @var callable $callable */
            $callable = [
                $stream,
                $diff,
            ];
            $methods[$diff] = $callable;
        }
        return new self($methods);
    }
    public function __toString() : string {
        try {
            
            /** @var string */
            return ($this->_fn___toString)();
        } catch (\Throwable $e) {
            if (\PHP_VERSION_ID >= 70400) {
                throw $e;
            }
            trigger_error(sprintf('%s::__toString exception: %s', self::class, (string) $e), E_USER_ERROR);
            return '';
        }
    }
    public function close() : void {
        ($this->_fn_close)();
    }
    public function detach() {
        return ($this->_fn_detach)();
    }
    public function getSize() : ?int {
        return ($this->_fn_getSize)();
    }
    public function tell() : int {
        return ($this->_fn_tell)();
    }
    public function eof() : bool {
        return ($this->_fn_eof)();
    }
    public function isSeekable() : bool {
        return ($this->_fn_isSeekable)();
    }
    public function rewind() : void {
        ($this->_fn_rewind)();
    }
    public function seek($offset, $whence = SEEK_SET) : void {
        ($this->_fn_seek)($offset, $whence);
    }
    public function isWritable() : bool {
        return ($this->_fn_isWritable)();
    }
    public function write($string) : int {
        return ($this->_fn_write)($string);
    }
    public function isReadable() : bool {
        return ($this->_fn_isReadable)();
    }
    public function read($length) : string {
        return ($this->_fn_read)($length);
    }
    public function getContents() : string {
        return ($this->_fn_getContents)();
    }
    
    /**
     * @return mixed
     */
    public function getMetadata($key = null) {
        return ($this->_fn_getMetadata)($key);
    }

}