interface CalculatedCacheContextInterface

interface CalculatedCacheContextInterface {
    
    /**
     * Returns the label of the cache context.
     *
     * @return string
     *   The label of the cache context.
     *
     * @see Cache
     */
    public static function getLabel();
    
    /**
     * Returns the string representation of the cache context.
     *
     * A cache context service's name is used as a token (placeholder) cache key,
     * and is then replaced with the string returned by this method.
     *
     * @param string|null $parameter
     *   The parameter, or NULL to indicate all possible parameter values.
     *
     * @return string
     *   The string representation of the cache context. When $parameter is NULL,
     *   a value representing all possible parameters must be generated.
     *
     * @throws \LogicException
     *   Thrown if the passed in parameter is invalid.
     */
    public function getContext($parameter = NULL);
    
    /**
     * Gets the cacheability metadata for the context based on the parameter value.
     *
     * There are three valid cases for the returned CacheableMetadata object:
     * - An empty object means this can be optimized away safely.
     * - A max-age of 0 means that this context can never be optimized away. It
     *   will never bubble up and cache tags will not be used.
     * - Any non-zero max-age and cache tags will bubble up into the cache item
     *   if this is optimized away to allow for invalidation if the context
     *   value changes.
     *
     * @param string|null $parameter
     *   The parameter, or NULL to indicate all possible parameter values.
     *
     * @return \Drupal\Core\Cache\CacheableMetadata
     *   A cacheable metadata object.
     *
     * @throws \LogicException
     *   Thrown if the passed in parameter is invalid.
     */
    public function getCacheableMetadata($parameter = NULL);

}