/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2006-2010 Sun Microsystems, Inc.
 * Portions Copyright 2011-2016 ForgeRock AS.
 */
package org.opends.server.replication.plugin;

import static org.opends.messages.ReplicationMessages.*;
import static org.opends.server.replication.plugin.HistAttrModificationKey.*;

import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import org.forgerock.i18n.slf4j.LocalizedLogger;
import org.forgerock.opendj.ldap.AttributeDescription;
import org.forgerock.opendj.ldap.ByteString;
import org.forgerock.opendj.ldap.ModificationType;
import org.forgerock.opendj.ldap.schema.AttributeType;
import org.opends.server.core.DirectoryServer;
import org.opends.server.replication.common.CSN;
import org.opends.server.replication.protocol.OperationContext;
import org.opends.server.types.Attribute;
import org.opends.server.types.AttributeBuilder;
import org.opends.server.types.Attributes;
import org.forgerock.opendj.ldap.DN;
import org.opends.server.types.Entry;
import org.opends.server.types.Modification;
import org.opends.server.types.operation.PreOperationAddOperation;
import org.opends.server.types.operation.PreOperationModifyDNOperation;
import org.opends.server.types.operation.PreOperationModifyOperation;
import org.opends.server.util.TimeThread;

/**
 * This class is used to store historical information that is used to resolve modify conflicts
 * <p>
 * It is assumed that the common case is not to have conflict and therefore is optimized (in order
 * of importance) for:
 * <ol>
 * <li>detecting potential conflict</li>
 * <li>fast update of historical information for non-conflicting change</li>
 * <li>fast and efficient purge</li>
 * <li>compact</li>
 * <li>solve conflict. This should also be as fast as possible but not at the cost of any of the
 * other previous objectives</li>
 * </ol>
 * One Historical object is created for each entry in the entry cache each Historical Object
 * contains a list of attribute historical information
 */
public class EntryHistorical
{
  private static final LocalizedLogger logger = LocalizedLogger.getLoggerForThisClass();

  /** Name of the attribute used to store historical information. */
  public static final String HISTORICAL_ATTRIBUTE_NAME = "ds-sync-hist";
  /**
   * Name used to store attachment of historical information in the
   * operation. This attachment allows to use in several different places
   * the historical while reading/writing ONCE it from/to the entry.
   */
  public static final String HISTORICAL = "ds-synch-historical";
  /** Name of the entryuuid attribute. */
  public static final String ENTRYUUID_ATTRIBUTE_NAME = "entryuuid";

  /**
   * The delay to purge the historical information.
   * <p>
   * This delay indicates the time the domain keeps the historical information
   * necessary to solve conflicts. When a change stored in the historical part
   * of the user entry has a date (from its replication CSN) older than this
   * delay, it is candidate to be purged. The purge is triggered on 2 events:
   * modify of the entry, dedicated purge task. The purge is done when the
   * historical is encoded.
   */
  private long purgeDelayInMillisec = -1;

  /**
   * The oldest CSN stored in this entry historical attribute.
   * null when this historical object has been created from
   * an entry that has no historical attribute and after the last
   * historical has been purged.
   */
  private CSN oldestCSN;

  /**
   * For stats/monitoring purpose, the number of historical values
   * purged the last time a purge has been applied on this entry historical.
   */
  private int lastPurgedValuesCount;

  /** The date when the entry was added. */
  private CSN entryADDDate;
  /** The date when the entry was last renamed. */
  private CSN entryMODDNDate;

  /** Contains Historical information for each attribute description. */
  private final Map<AttributeDescription, AttrHistorical> attributesHistorical = new HashMap<>();

  @Override
  public String toString()
  {
    StringBuilder builder = new StringBuilder();
    builder.append(encodeAndPurge());
    return builder.toString();
  }

  /**
   * Process an operation.
   * This method is responsible for detecting and resolving conflict for
   * modifyOperation. This is done by using the historical information.
   *
   * @param modifyOperation the operation to be processed
   * @param modifiedEntry the entry that is being modified (before modification)
   * @return true if the replayed operation was in conflict
   */
  public boolean replayOperation(PreOperationModifyOperation modifyOperation, Entry modifiedEntry)
  {
    boolean bConflict = false;
    List<Modification> mods = modifyOperation.getModifications();
    CSN modOpCSN = OperationContext.getCSN(modifyOperation);

    for (Iterator<Modification> it = mods.iterator(); it.hasNext(); )
    {
      Modification m = it.next();

      // Read or create the attr historical for the attribute type and option
      // contained in the mod
      AttrHistorical attrHist = getOrCreateAttrHistorical(m);
      if (attrHist.replayOperation(it, modOpCSN, modifiedEntry, m))
      {
        bConflict = true;
      }
    }

    return bConflict;
  }

  /**
   * Update the historical information for the provided operation.
   * <p>
   * Steps:
   * <ul>
   * <li>compute the historical attribute</li>
   * <li>update the mods in the provided operation by adding the update of the
   * historical attribute</li>
   * <li>update the modifiedEntry, already computed by core since we are in the
   * preOperation plugin, that is called just before committing into the DB.
   * </li>
   * </ul>
   * </p>
   *
   * @param modifyOperation
   *          the modification.
   */
  public void setHistoricalAttrToOperation(PreOperationModifyOperation modifyOperation)
  {
    List<Modification> mods = modifyOperation.getModifications();
    Entry modifiedEntry = modifyOperation.getModifiedEntry();
    CSN csn = OperationContext.getCSN(modifyOperation);

    /*
     * If this is a local operation we need :
     * - first to update the historical information,
     * - then update the entry with the historical information
     * If this is a replicated operation the historical information has
     * already been set in the resolveConflict phase and we only need
     * to update the entry
     */
    if (!modifyOperation.isSynchronizationOperation())
    {
      for (Modification mod : mods)
      {
        // Get the current historical for this attributeType/options
        // (eventually read from the provided modification)
        AttrHistorical attrHist = getOrCreateAttrHistorical(mod);
        if (attrHist != null)
        {
          attrHist.processLocalOrNonConflictModification(csn, mod);
        }
      }
    }

    // Now do the 2 updates required by the core to be consistent:
    //
    // - add the modification of the ds-sync-hist attribute,
    // to the current modifications of the MOD operation
    Attribute attr = encodeAndPurge();
    mods.add(new Modification(ModificationType.REPLACE, attr));
    // - update the already modified entry
    modifiedEntry.replaceAttribute(attr);
  }

  /**
   * For a MODDN operation, add new or update existing historical information.
   * <p>
   * This method is NOT static because it relies on this Historical object created in the
   * HandleConflictResolution phase.
   *
   * @param modifyDNOperation
   *          the modification for which the historical information should be created.
   */
  public void setHistoricalAttrToOperation(PreOperationModifyDNOperation modifyDNOperation)
  {
    // Update this historical information with the operation CSN.
    this.entryMODDNDate = OperationContext.getCSN(modifyDNOperation);

    // Update the operations mods and the modified entry so that the
    // historical information gets stored in the DB and indexed accordingly.
    Entry modifiedEntry = modifyDNOperation.getUpdatedEntry();
    List<Modification> mods = modifyDNOperation.getModifications();

    Attribute attr = encodeAndPurge();

    // Now do the 2 updates required by the core to be consistent:
    //
    // - add the modification of the ds-sync-hist attribute,
    // to the current modifications of the operation
    mods.add(new Modification(ModificationType.REPLACE, attr));
    // - update the already modified entry
    modifiedEntry.removeAttribute(attr.getAttributeDescription().getAttributeType());
    modifiedEntry.addAttribute(attr, null);
  }

  /**
   * Generate an attribute containing the historical information
   * from the replication context attached to the provided operation
   * and set this attribute in the operation.
   *
   *   For ADD, the historical is made of the CSN read from the
   *   synchronization context attached to the operation.
   *
   *   Called for both local and synchronization ADD preOperation.
   *
   *   This historical information will be used to generate fake operation
   *   in case a Directory Server can not find a Replication Server with
   *   all its changes at connection time.
   *   This should only happen if a Directory Server or a Replication Server
   *   crashes.
   *
   *   This method is static because there is no Historical object creation
   *   required here or before(in the HandleConflictResolution phase)
   *
   * @param addOperation The Operation to which the historical attribute will be added.
   */
  public static void setHistoricalAttrToOperation(PreOperationAddOperation addOperation)
  {
    AttributeType attrType = DirectoryServer.getAttributeType(HISTORICAL_ATTRIBUTE_NAME);
    String attrValue = encodeHistorical(OperationContext.getCSN(addOperation), "add");
    List<Attribute> attrs = Attributes.createAsList(attrType, attrValue);
    addOperation.setAttribute(attrType, attrs);
  }

  /**
   * Builds an attributeValue for the supplied historical information and
   * operation type . For ADD Operation : "dn:changeNumber:add", for MODDN
   * Operation : "dn:changeNumber:moddn", etc.
   *
   * @param csn
   *          The date when the ADD Operation happened.
   * @param operationType
   *          the operation type to encode
   * @return The attribute value containing the historical information for the Operation type.
   */
  private static String encodeHistorical(CSN csn, String operationType)
  {
    return "dn:" + csn + ":" + operationType;
  }

  /**
   * Return an AttributeHistorical corresponding to the attribute type
   * and options contained in the provided mod,
   * The attributeHistorical is :
   * - either read from this EntryHistorical object if one exist,
   * - or created empty.
   * Should never return null.
   *
   * @param  mod the provided mod from which we'll use attributeType
   *             and options to retrieve/create the attribute historical
   * @return the attribute historical retrieved or created empty.
   */
  private AttrHistorical getOrCreateAttrHistorical(Modification mod)
  {
    // Read the provided mod
    Attribute modAttr = mod.getAttribute();
    if (isHistoricalAttribute(modAttr))
    {
      // Don't keep historical information for the attribute that is
      // used to store the historical information.
      return null;
    }

    // Read from this entryHistorical,
    // Create one empty if none was existing in this entryHistorical.
    AttributeDescription attrDesc = modAttr.getAttributeDescription();
    AttrHistorical attrHist = attributesHistorical.get(attrDesc);
    if (attrHist == null)
    {
      attrHist = AttrHistorical.createAttributeHistorical(modAttr.getAttributeDescription().getAttributeType());
      attributesHistorical.put(attrDesc, attrHist);
    }
    return attrHist;
  }

  /**
   * For stats/monitoring purpose, returns the number of historical values
   * purged the last time a purge has been applied on this entry historical.
   *
   * @return the purged values count.
   */
  public int getLastPurgedValuesCount()
  {
    return this.lastPurgedValuesCount;
  }

  /**
   * Encode this historical information object in an operational attribute and
   * purge it from the values older than the purge delay.
   *
   * @return The historical information encoded in an operational attribute.
   * @see HistoricalAttributeValue#HistoricalAttributeValue(String) the decode
   *      operation in HistoricalAttributeValue
   */
  public Attribute encodeAndPurge()
  {
    long purgeDate = 0;

    // Set the stats counter to 0 and compute the purgeDate to now minus
    // the potentially set purge delay.
    this.lastPurgedValuesCount = 0;
    if (purgeDelayInMillisec>0)
    {
      purgeDate = TimeThread.getTime() - purgeDelayInMillisec;
    }

    AttributeBuilder builder = new AttributeBuilder(HISTORICAL_ATTRIBUTE_NAME);

    for (Map.Entry<AttributeDescription, AttrHistorical> mapEntry : attributesHistorical.entrySet())
    {
      AttributeDescription attrDesc = mapEntry.getKey();
      String options = attrDesc.toString();
      AttrHistorical attrHist = mapEntry.getValue();

      CSN deleteTime = attrHist.getDeleteTime();
      /* generate the historical information for deleted attributes */
      boolean attrDel = deleteTime != null;

      for (AttrValueHistorical attrValHist : attrHist.getValuesHistorical())
      {
        final ByteString value = attrValHist.getAttributeValue();

        // Encode an attribute value
        if (attrValHist.getValueDeleteTime() != null)
        {
          if (needsPurge(attrValHist.getValueDeleteTime(), purgeDate))
          {
            // this hist must be purged now, so skip its encoding
            continue;
          }
          String strValue = encode(DEL, options, attrValHist.getValueDeleteTime(), value);
          builder.add(strValue);
        }
        else if (attrValHist.getValueUpdateTime() != null)
        {
          if (needsPurge(attrValHist.getValueUpdateTime(), purgeDate))
          {
            // this hist must be purged now, so skip its encoding
            continue;
          }

          String strValue;
          final CSN updateTime = attrValHist.getValueUpdateTime();
          // FIXME very suspicious use of == in the next if statement,
          // unit tests do not like changing it
          if (attrDel && updateTime == deleteTime && value != null)
          {
            strValue = encode(REPL, options, updateTime, value);
            attrDel = false;
          }
          else if (value != null)
          {
            strValue = encode(ADD, options, updateTime, value);
          }
          else
          {
            // "add" without any value is suspicious. Tests never go there.
            // Is this used to encode "add" with an empty string?
            strValue = encode(ADD, options, updateTime);
          }

          builder.add(strValue);
        }
      }

      if (attrDel)
      {
        if (needsPurge(deleteTime, purgeDate))
        {
          // this hist must be purged now, so skip its encoding
          continue;
        }
        builder.add(encode(ATTRDEL, options, deleteTime));
      }
    }

    if (entryADDDate != null && !needsPurge(entryADDDate, purgeDate))
    {
      // Encode the historical information for the ADD Operation.
      // Stores the ADDDate when not older than the purge delay
      builder.add(encodeHistorical(entryADDDate, "add"));
    }

    if (entryMODDNDate != null && !needsPurge(entryMODDNDate, purgeDate))
    {
      // Encode the historical information for the MODDN Operation.
      // Stores the MODDNDate when not older than the purge delay
      builder.add(encodeHistorical(entryMODDNDate, "moddn"));
    }

    return builder.toAttribute();
  }

  private boolean needsPurge(CSN csn, long purgeDate)
  {
    boolean needsPurge = purgeDelayInMillisec > 0 && csn.getTime() <= purgeDate;
    if (needsPurge)
    {
      // this hist must be purged now, because older than the purge delay
      this.lastPurgedValuesCount++;
    }
    return needsPurge;
  }

  private String encode(HistAttrModificationKey modKey, String options, CSN changeTime)
  {
    return options + ":" + changeTime + ":" + modKey;
  }

  private String encode(HistAttrModificationKey modKey, String options, CSN changeTime, ByteString value)
  {
    return options + ":" + changeTime + ":" + modKey + ":" + value;
  }

  /**
   * Set the delay to purge the historical information. The purge is applied
   * only when historical attribute is updated (write operations).
   *
   * @param purgeDelay the purge delay in ms
   */
  public void setPurgeDelay(long purgeDelay)
  {
    this.purgeDelayInMillisec = purgeDelay;
  }

  /**
   * Indicates if the Entry was renamed or added after the CSN that is given as
   * a parameter.
   *
   * @param csn
   *          The CSN with which the ADD or Rename date must be compared.
   * @return A boolean indicating if the Entry was renamed or added after the
   *         CSN that is given as a parameter.
   */
  public boolean addedOrRenamedAfter(CSN csn)
  {
    return csn.isOlderThan(entryADDDate) || csn.isOlderThan(entryMODDNDate);
  }

  /**
   * Returns the lastCSN when the entry DN was modified.
   *
   * @return The lastCSN when the entry DN was modified.
   */
  public CSN getDNDate()
  {
    if (entryADDDate == null)
    {
      return entryMODDNDate;
    }
    if (entryMODDNDate == null)
    {
      return entryADDDate;
    }

    if (entryMODDNDate.isOlderThan(entryADDDate))
    {
      return entryMODDNDate;
    }
    else
    {
      return entryADDDate;
    }
  }

  /**
   * Construct an Historical object from the provided entry by reading the historical attribute.
   * Return an empty object when the entry does not contain any historical attribute.
   *
   * @param entry The entry which historical information must be loaded
   * @return The constructed Historical information object
   */
  public static EntryHistorical newInstanceFromEntry(Entry entry)
  {
    // Read the DB historical attribute from the entry
    List<Attribute> histAttrWithOptionsFromEntry = getHistoricalAttr(entry);

    // Now we'll build the Historical object we want to construct
    final EntryHistorical newHistorical = new EntryHistorical();
    if (histAttrWithOptionsFromEntry.isEmpty())
    {
      // No historical attribute in the entry, return empty object
      return newHistorical;
    }

    try
    {
      // For each value of the historical attr read (mod. on a user attribute)
      //   build an AttrInfo sub-object

      // Traverse the Attributes (when several options for the hist attr)
      // of the historical attribute read from the entry
      for (Attribute histAttrFromEntry : histAttrWithOptionsFromEntry)
      {
        // For each Attribute (option), traverse the values
        for (ByteString histAttrValueFromEntry : histAttrFromEntry)
        {
          // From each value of the hist attr, create an object
          final HistoricalAttributeValue histVal = new HistoricalAttributeValue(histAttrValueFromEntry.toString());
          final CSN csn = histVal.getCSN();

          // update the oldest CSN stored in the new entry historical
          newHistorical.updateOldestCSN(csn);

          if (histVal.isADDOperation())
          {
            newHistorical.entryADDDate = csn;
          }
          else if (histVal.isMODDNOperation())
          {
            newHistorical.entryMODDNDate = csn;
          }
          else
          {
            AttributeDescription attrDesc = histVal.getAttributeDescription();
            if (attrDesc == null)
            {
              /*
               * This attribute is unknown from the schema
               * Just skip it, the modification will be processed but no
               * historical information is going to be kept.
               * Log information for the repair tool.
               */
              logger.error(ERR_UNKNOWN_ATTRIBUTE_IN_HISTORICAL, entry.getName(), histVal.getAttrString());
              continue;
            }

            /* if attribute type does not match we create new
             *   AttrInfoWithOptions and AttrInfo
             *   we also add old AttrInfoWithOptions into histObj.attributesInfo
             * if attribute type match but options does not match we create new
             *   AttrInfo that we add to AttrInfoWithOptions
             * if both match we keep everything
             */
            AttrHistorical attrInfo = newHistorical.attributesHistorical.get(attrDesc);
            if (attrInfo == null)
            {
              attrInfo = AttrHistorical.createAttributeHistorical(attrDesc.getAttributeType());
              newHistorical.attributesHistorical.put(attrDesc, attrInfo);
            }
            attrInfo.assign(histVal.getHistKey(), histVal.getAttributeValue(), csn);
          }
        }
      }
    } catch (Exception e)
    {
      // Any exception happening here means that the coding of the historical
      // information was wrong.
      // Log an error and continue with an empty historical.
      logger.error(ERR_BAD_HISTORICAL, entry.getName());
    }

    /* set the reference to the historical information in the entry */
    return newHistorical;
  }

  /**
   * Use this historical information to generate fake operations that would
   * result in this historical information.
   * TODO : This is only implemented for MODIFY, MODRDN and ADD
   *        need to complete with DELETE.
   * @param entry The Entry to use to generate the FakeOperation Iterable.
   *
   * @return an Iterable of FakeOperation that would result in this historical information.
   */
  public static Iterable<FakeOperation> generateFakeOperations(Entry entry)
  {
    TreeMap<CSN, FakeOperation> operations = new TreeMap<>();
    for (Attribute attr : getHistoricalAttr(entry))
    {
      for (ByteString val : attr)
      {
        HistoricalAttributeValue histVal = new HistoricalAttributeValue(val.toString());
        if (histVal.isADDOperation())
        {
          // Found some historical information indicating that this entry was just added.
          // Create the corresponding ADD operation.
          operations.put(histVal.getCSN(), new FakeAddOperation(histVal.getCSN(), entry));
        }
        else if (histVal.isMODDNOperation())
        {
          // Found some historical information indicating that this entry was just renamed.
          // Create the corresponding ADD operation.
          operations.put(histVal.getCSN(), new FakeModdnOperation(histVal.getCSN(), entry));
        }
        else
        {
          // Found some historical information for modify operation.
          // Generate the corresponding ModifyOperation or update
          // the already generated Operation if it can be found.
          CSN csn = histVal.getCSN();
          Modification mod = histVal.generateMod();
          FakeOperation fakeOperation = operations.get(csn);

          if (fakeOperation instanceof FakeModifyOperation)
          {
            FakeModifyOperation modifyFakeOperation = (FakeModifyOperation) fakeOperation;
            modifyFakeOperation.addModification(mod);
          }
          else
          {
            String uuidString = getEntryUUID(entry);
            FakeModifyOperation modifyFakeOperation = new FakeModifyOperation(entry.getName(), csn, uuidString);
            modifyFakeOperation.addModification(mod);
            operations.put(histVal.getCSN(), modifyFakeOperation);
          }
        }
      }
    }
    return operations.values();
  }

  /**
   * Get the attribute used to store the historical information from the provided Entry.
   *
   * @param   entry  The entry containing the historical information.
   * @return  The Attribute used to store the historical information.
   *          Several values on the list if several options for this attribute.
   *          Null if not present.
   */
  public static List<Attribute> getHistoricalAttr(Entry entry)
  {
    return entry.getAttribute(HISTORICAL_ATTRIBUTE_NAME);
  }

  /**
   * Get the entry unique Id in String form.
   *
   * @param entry The entry for which the unique id should be returned.
   * @return The Unique Id of the entry, or a fake one if none is found.
   */
  public static String getEntryUUID(Entry entry)
  {
    AttributeType attrType = DirectoryServer.getAttributeType(ENTRYUUID_ATTRIBUTE_NAME);
    List<Attribute> uuidAttrs = entry.getOperationalAttribute(attrType);
    return extractEntryUUID(uuidAttrs, entry.getName());
  }

  /**
   * Get the Entry Unique Id from an add operation.
   * This must be called after the entry uuid pre-op plugin (i.e no
   * sooner than the replication provider pre-op)
   *
   * @param op The operation
   * @return The Entry Unique Id String form.
   */
  public static String getEntryUUID(PreOperationAddOperation op)
  {
    AttributeType attrType = DirectoryServer.getAttributeType(ENTRYUUID_ATTRIBUTE_NAME);
    List<Attribute> uuidAttrs = op.getOperationalAttributes().get(attrType);
    return extractEntryUUID(uuidAttrs, op.getEntryDN());
  }

  /**
   * Check if a given attribute is an attribute used to store historical
   * information.
   *
   * @param   attr The attribute that needs to be checked.
   *
   * @return  a boolean indicating if the given attribute is
   *          used to store historical information.
   */
  public static boolean isHistoricalAttribute(Attribute attr)
  {
    AttributeType attrType = attr.getAttributeDescription().getAttributeType();
    return HISTORICAL_ATTRIBUTE_NAME.equals(attrType.getNameOrOID());
  }

  /**
   * Potentially update the oldest CSN stored in this entry historical
   * with the provided CSN when its older than the current oldest.
   *
   * @param csn the provided CSN.
   */
  private void updateOldestCSN(CSN csn)
  {
    if (csn != null
        && (this.oldestCSN == null || csn.isOlderThan(this.oldestCSN)))
    {
      this.oldestCSN = csn;
    }
  }

  /**
   * Returns the oldest CSN stored in this entry historical attribute.
   *
   * @return the oldest CSN stored in this entry historical attribute.
   *         Returns null when this historical object has been created from
   *         an entry that has no historical attribute and after the last
   *         historical has been purged.
   */
  public CSN getOldestCSN()
  {
    return this.oldestCSN;
  }

  /**
   * Extracts the entryUUID attribute value from the provided list of
   * attributes. If the attribute is not present one is generated from the DN
   * using the same algorithm as the entryUUID virtual attribute provider.
   */
  private static String extractEntryUUID(List<Attribute> entryUUIDAttributes, DN entryDN)
  {
    if (!entryUUIDAttributes.isEmpty())
    {
      Attribute uuidAttr = entryUUIDAttributes.get(0);
      if (!uuidAttr.isEmpty())
      {
        return uuidAttr.iterator().next().toString();
      }
    }

    // Generate a fake entryUUID: see OPENDJ-181. In rare pathological cases
    // an entryUUID attribute may not be present and this causes severe side effects
    // for replication which requires the attribute to always be present
    if (logger.isTraceEnabled())
    {
      logger.trace(
          "Replication requires an entryUUID attribute in order "
              + "to perform conflict resolution, but none was "
              + "found in entry \"%s\": generating virtual entryUUID instead",
          entryDN);
    }

    return entryDN.toUUID().toString();
  }
}