class Context

class Context extends ComponentContext implements ContextInterface {
    use TypedDataTrait;
    use DependencySerializationTrait;
    
    /**
     * The data associated with the context.
     *
     * @var \Drupal\Core\TypedData\TypedDataInterface
     */
    protected $contextData;
    
    /**
     * The definition to which a context must conform.
     *
     * @var \Drupal\Core\Plugin\Context\ContextDefinitionInterface
     */
    protected $contextDefinition;
    
    /**
     * The cacheability metadata.
     *
     * @var \Drupal\Core\Cache\CacheableMetadata
     */
    protected $cacheabilityMetadata;
    
    /**
     * Create a context object.
     *
     * @param \Drupal\Core\Plugin\Context\ContextDefinitionInterface $context_definition
     *   The context definition.
     * @param mixed|null $context_value
     *   The context value object.
     */
    public function __construct(ContextDefinitionInterface $context_definition, $context_value = NULL) {
        parent::__construct($context_definition, NULL);
        $this->cacheabilityMetadata = new CacheableMetadata();
        if (!is_null($context_value)) {
            $this->setContextValue($context_value);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextValue() {
        if (!isset($this->contextData)) {
            $definition = $this->getContextDefinition();
            $default_value = $definition->getDefaultValue();
            if (isset($default_value)) {
                // Keep the default value here so that subsequent calls don't have to
                // look it up again.
                $this->setContextValue($default_value);
            }
            elseif ($definition->isRequired()) {
                $type = $definition->getDataType();
                throw new ContextException("The '{$type}' context is required and not present.");
            }
            return $default_value;
        }
        return $this->getTypedDataManager()
            ->getCanonicalRepresentation($this->contextData);
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasContextValue() {
        return (bool) $this->contextData || parent::hasContextValue();
    }
    
    /**
     * Sets the context value.
     *
     * @param mixed $value
     *   The value of this context, matching the context definition.
     */
    protected function setContextValue($value) {
        // Add the value as a cacheable dependency only if implements the interface
        // to prevent it from disabling caching with a max-age 0.
        if ($value instanceof CacheableDependencyInterface) {
            $this->addCacheableDependency($value);
        }
        if ($value instanceof TypedDataInterface) {
            $this->contextData = $value;
        }
        else {
            $this->contextData = $this->getTypedDataManager()
                ->create($this->contextDefinition
                ->getDataDefinition(), $value);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConstraints() {
        return $this->contextDefinition
            ->getConstraints();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextData() {
        if (!isset($this->contextData)) {
            $definition = $this->getContextDefinition();
            $default_value = $definition->getDefaultValue();
            // Store the default value so that subsequent calls don't have to look
            // it up again.
            $this->contextData = $this->getTypedDataManager()
                ->create($definition->getDataDefinition(), $default_value);
        }
        return $this->contextData;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextDefinition() {
        return $this->contextDefinition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate() {
        return $this->getContextData()
            ->validate();
    }
    
    /**
     * {@inheritdoc}
     */
    public function addCacheableDependency($dependency) {
        $this->cacheabilityMetadata = $this->cacheabilityMetadata
            ->merge(CacheableMetadata::createFromObject($dependency));
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        return $this->cacheabilityMetadata
            ->getCacheContexts();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheTags() {
        return $this->cacheabilityMetadata
            ->getCacheTags();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheMaxAge() {
        return $this->cacheabilityMetadata
            ->getCacheMaxAge();
    }
    
    /**
     * {@inheritdoc}
     */
    public static function createFromContext(ContextInterface $old_context, $value) {
        $context = new static($old_context->getContextDefinition(), $value);
        $context->addCacheableDependency($old_context);
        if (method_exists($old_context, 'getTypedDataManager')) {
            $context->setTypedDataManager($old_context->getTypedDataManager());
        }
        return $context;
    }

}