class ContextAwarePluginBase

abstract class ContextAwarePluginBase extends PluginBase implements ContextAwarePluginInterface {
    
    /**
     * The data objects representing the context of this plugin.
     *
     * @var \Drupal\Component\Plugin\Context\ContextInterface[]
     */
    protected $context = [];
    
    /**
     * Data objects representing the contexts passed in the plugin configuration.
     *
     * @var \Drupal\Component\Plugin\Context\ContextInterface[]
     *
     * @deprecated
     *   in drupal:8.8.0 and is removed from drupal:9.0.0. Use
     *   \Drupal\Component\Plugin\ContextAwarePluginInterface instead.
     *
     * @see https://www.drupal.org/project/drupal/issues/3080631
     */
    private $contexts = [];
    
    /**
     * Overrides \Drupal\Component\Plugin\PluginBase::__construct().
     *
     * Overrides the construction of context aware plugins to allow for
     * unvalidated constructor based injection of contexts.
     *
     * @param array $configuration
     *   The plugin configuration, i.e. an array with configuration values keyed
     *   by configuration option name. The special key 'context' may be used to
     *   initialize the defined contexts by setting it to an array of context
     *   values keyed by context names.
     * @param string $plugin_id
     *   The plugin_id for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition) {
        $context_configuration = isset($configuration['context']) ? $configuration['context'] : [];
        unset($configuration['context']);
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->context = $this->createContextFromConfiguration($context_configuration);
        // @todo Remove $this->contexts in Drupal 9; see
        // https://www.drupal.org/project/drupal/issues/3081145
        $this->contexts = $this->context;
    }
    
    /**
     * Implements magic __get() method.
     */
    public function __get($name) {
        if ($name === 'contexts') {
            @trigger_error('The $contexts property is deprecated in Drupal 8.8.0 and will be removed before Drupal 9.0.0. Use methods of \\Drupal\\Component\\Plugin\\ContextAwarePluginInterface instead. See https://www.drupal.org/project/drupal/issues/3080631 for more information.', E_USER_DEPRECATED);
            return $this->contexts;
        }
    }
    
    /**
     * Creates context objects from any context mappings in configuration.
     *
     * @param array $context_configuration
     *   An associative array of context names and values.
     *
     * @return \Drupal\Component\Plugin\Context\ContextInterface[]
     *   An array of context objects.
     */
    protected function createContextFromConfiguration(array $context_configuration) {
        $contexts = [];
        foreach ($context_configuration as $key => $value) {
            $context_definition = $this->getContextDefinition($key);
            $contexts[$key] = new Context($context_definition, $value);
        }
        return $contexts;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextDefinitions() {
        $definition = $this->getPluginDefinition();
        if ($definition instanceof ContextAwarePluginDefinitionInterface) {
            return $definition->getContextDefinitions();
        }
        else {
            return !empty($definition['context_definitions']) ? $definition['context_definitions'] : [];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextDefinition($name) {
        $definition = $this->getPluginDefinition();
        if ($definition instanceof ContextAwarePluginDefinitionInterface) {
            if ($definition->hasContextDefinition($name)) {
                return $definition->getContextDefinition($name);
            }
        }
        elseif (!empty($definition['context_definitions'][$name])) {
            return $definition['context_definitions'][$name];
        }
        throw new ContextException(sprintf("The %s context is not a valid context.", $name));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContexts() {
        // Make sure all context objects are initialized.
        foreach ($this->getContextDefinitions() as $name => $definition) {
            $this->getContext($name);
        }
        return $this->context;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContext($name) {
        // Check for a valid context value.
        if (!isset($this->context[$name])) {
            $this->context[$name] = new Context($this->getContextDefinition($name));
        }
        return $this->context[$name];
    }
    
    /**
     * {@inheritdoc}
     */
    public function setContext($name, ContextInterface $context) {
        $this->context[$name] = $context;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextValues() {
        $values = [];
        foreach ($this->getContextDefinitions() as $name => $definition) {
            $values[$name] = isset($this->context[$name]) ? $this->context[$name]
                ->getContextValue() : NULL;
        }
        return $values;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getContextValue($name) {
        return $this->getContext($name)
            ->getContextValue();
    }
    
    /**
     * {@inheritdoc}
     */
    public function setContextValue($name, $value) {
        $this->context[$name] = new Context($this->getContextDefinition($name), $value);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateContexts() {
        $violations = new ConstraintViolationList();
        // @todo: Implement symfony validator API to let the validator traverse
        // and set property paths accordingly.
        foreach ($this->getContexts() as $context) {
            $violations->addAll($context->validate());
        }
        return $violations;
    }

}