interface CacheContextInterface

interface CacheContextInterface {
    
    /**
     * Returns the label of the cache context.
     *
     * @return string
     *   The label of the cache context.
     */
    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.
     *
     * @return string
     *   The string representation of the cache context.
     */
    public function getContext();
    
    /**
     * Gets the cacheability metadata for the context.
     *
     * 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.
     *
     *
     * @return \Drupal\Core\Cache\CacheableMetadata
     *   A cacheable metadata object.
     */
    public function getCacheableMetadata();

}