package gw.solr.consistency

uses org.json.simple.JSONObject


/**
 * Interface that provides a mapping from the URN for a Solr document
 * to the key that is used for the consistency cache to match related
 * Solr document updates and deletes.
 * 
 * Pass an implementation of this interface to the consistency tracker
 * builder that provides the appropriate mapping (such as stripping or
 * modifying a digest key).  Defaults to using the URN for the key,
 * which will be correct for most cases.
 */
@ReadOnly
interface IKeyGenerator {
  
  /**
   * Create the consistency cache key to be used for this URN.  For a
   * given key, only the most recent update to that key will be cached
   * for consistency checking purposes.
   * 
   * IMPORTANT : Implementations of this class must be thread safe!
   * 
   * @param docObj a json representation of the document for which the 
   *   key is being created
   * @param urnTag the label used for the unique resource id of this document.
   *   This can be different for deletes vs updates
   * @return the key to use for the consistency cache
   */
  function createKey( docObj : JSONObject, urnTag : String ) : String

}