/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE
 * or https://OpenDS.dev.java.net/OpenDS.LICENSE.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at
 * trunk/opends/resource/legal-notices/OpenDS.LICENSE.  If applicable,
 * add the following below this CDDL HEADER, with the fields enclosed
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 *
 *
 *      Copyright 2006-2010 Sun Microsystems, Inc.
 *      Portions copyright 2012-2013 ForgeRock AS.
 */
package org.opends.server.replication.plugin;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;

import org.opends.messages.Message;
import org.opends.server.core.DirectoryServer;
import org.opends.server.core.ModifyOperationBasis;
import org.opends.server.protocols.internal.InternalClientConnection;
import org.opends.server.protocols.internal.InternalSearchOperation;
import org.opends.server.protocols.ldap.LDAPAttribute;
import org.opends.server.protocols.ldap.LDAPModification;
import org.opends.server.replication.common.CSN;
import org.opends.server.replication.common.ServerState;
import org.opends.server.types.*;

import static org.opends.messages.ReplicationMessages.*;
import static org.opends.server.loggers.ErrorLogger.*;

/**
 * This class implements a ServerState that is stored in the backend
 * used to store the synchronized data and that is therefore persistent
 * across server reboot.
 */
public class PersistentServerState
{
   private final DN baseDn;
   private final InternalClientConnection conn =
       InternalClientConnection.getRootConnection();
   private final int serverId;

   private final ServerState state;

   /**
    * The attribute name used to store the state in the backend.
    */
   protected static final String REPLICATION_STATE = "ds-sync-state";

  /**
   * create a new ServerState.
   * @param baseDn The baseDN for which the ServerState is created
   * @param serverId The serverId
   */
  public PersistentServerState(DN baseDn, int serverId)
  {
    this.baseDn = baseDn;
    this.serverId = serverId;
    this.state = new ServerState();
    loadState();
  }

  /**
   * Create a new PersistentServerState based on an already existing
   * ServerState.
   *
   * @param baseDn    The baseDN for which the ServerState is created.
   * @param serverId  The serverId.
   * @param state     The serverState.
   */
  public PersistentServerState(DN baseDn, int serverId, ServerState state)
  {
    this.baseDn = baseDn;
    this.serverId = serverId;
    this.state = state;
    loadState();
  }

  /**
   * Checks that the CSN given as a parameter is in this ServerState.
   *
   * @param   covered The CSN that should be checked.
   * @return  A boolean indicating if this ServerState contains the CSN
   *          given in parameter.
   */
  public boolean cover(CSN covered)
  {
    return state.cover(covered);
  }

  /**
   * Update the Server State with a CSN. All operations with smaller CSN and the
   * same serverID must be committed before calling this method.
   *
   * @param csn
   *          The committed CSN.
   * @return a boolean indicating if the update was meaningful.
   */
  public boolean update(CSN csn)
  {
    return state.update(csn);
  }

  /**
   * Save this object to persistent storage.
   */
  public void save()
  {
    if (state.isSaved())
      return;

    state.setSaved(true);
    ResultCode resultCode = updateStateEntry();
    if (resultCode != ResultCode.SUCCESS)
    {
      state.setSaved(false);
    }
  }

  /**
   * Load the ServerState from the backing entry in database to memory.
   */
  public void loadState()
  {
    // try to load the state from the base entry.
    SearchResultEntry stateEntry = searchBaseEntry();
    if (stateEntry == null)
    {
      /*
      The base entry does not exist yet in the database or was deleted.
      Try to read the ServerState from the configuration instead.
      */
      stateEntry = searchConfigEntry();
    }

    if (stateEntry != null)
    {
      updateStateFromEntry(stateEntry);
    }

    /*
     * In order to make sure that the replication never looses changes,
     * the server needs to search all the entries that have been
     * updated after the last write of the ServerState.
     * Inconsistencies may append after a crash.
     */
    checkAndUpdateServerState();
  }

  /**
   * Run a search operation to find the base entry
   * of the replication domain for which this ServerState was created.
   *
   * @return The base entry or null if no entry was found;
   */
  private SearchResultEntry searchBaseEntry()
  {
    try
    {
      SearchFilter filter =
          SearchFilter.createFilterFromString("objectclass=*");
      /*
       * Search the database entry that is used to periodically
       * save the ServerState
       */
      LinkedHashSet<String> attributes = new LinkedHashSet<String>(1);
      attributes.add(REPLICATION_STATE);
      InternalSearchOperation search = conn.processSearch(baseDn,
          SearchScope.BASE_OBJECT,
          DereferencePolicy.NEVER_DEREF_ALIASES,
          0, 0, false, filter, attributes);
      if (((search.getResultCode() != ResultCode.SUCCESS)) &&
          ((search.getResultCode() != ResultCode.NO_SUCH_OBJECT)))
      {
        Message message = ERR_ERROR_SEARCHING_RUV.
            get(search.getResultCode().getResultCodeName(), search.toString(),
                search.getErrorMessage(), baseDn.toString());
        logError(message);
        return null;
      }

      SearchResultEntry stateEntry = null;
      if (search.getResultCode() == ResultCode.SUCCESS)
      {
        // Read the serverState from the REPLICATION_STATE attribute
        LinkedList<SearchResultEntry> result = search.getSearchEntries();
        if (!result.isEmpty())
        {
          stateEntry = result.getFirst();
        }
      }
      return stateEntry;
    }
    catch (DirectoryException e)
    {
      // cannot happen
      return null;
    }
  }

  /**
   * Run a search operation to find the entry with the configuration
   * of the replication domain for which this ServerState was created.
   *
   * @return The configuration Entry or null if no entry was found;
   */
  private SearchResultEntry searchConfigEntry()
  {
    try
    {
      SearchFilter filter =
        SearchFilter.createFilterFromString(
            "(&(objectclass=ds-cfg-replication-domain)"
            +"(ds-cfg-base-dn="+baseDn+"))");

      LinkedHashSet<String> attributes = new LinkedHashSet<String>(1);
      attributes.add(REPLICATION_STATE);
      InternalSearchOperation op =
          conn.processSearch(DN.decode("cn=config"),
          SearchScope.SUBORDINATE_SUBTREE,
          DereferencePolicy.NEVER_DEREF_ALIASES,
          1, 0, false, filter, attributes);

      if (op.getResultCode() == ResultCode.SUCCESS)
      {
        // Read the serverState from the REPLICATION_STATE attribute
        LinkedList<SearchResultEntry> resultEntries =
          op.getSearchEntries();
        if (!resultEntries.isEmpty())
        {
          return resultEntries.getFirst();
        }
      }
      return null;
    } catch (DirectoryException e)
    {
      // can not happen
      return null;
    }
  }

  /**
   * Update this ServerState from the provided entry.
   *
   * @param resultEntry The entry that should be used to update this
   *                    ServerState.
   */
  private void updateStateFromEntry(SearchResultEntry resultEntry)
  {
    AttributeType synchronizationStateType =
      DirectoryServer.getAttributeType(REPLICATION_STATE);
    List<Attribute> attrs =
      resultEntry.getAttribute(synchronizationStateType);
    if (attrs != null)
    {
      Attribute attr = attrs.get(0);
      for (AttributeValue value : attr)
      {
        update(new CSN(value.toString()));
      }
    }
  }

  /**
   * Save the current values of this PersistentState object
   * in the appropriate entry of the database.
   *
   * @return a ResultCode indicating if the method was successful.
   */
  private ResultCode updateStateEntry()
  {
    /*
     * Generate a modify operation on the Server State baseD Entry.
     */
    ResultCode result = runUpdateStateEntry(baseDn);

    if (result == ResultCode.NO_SUCH_OBJECT)
    {
      // The base entry does not exist yet in the database or
      // has been deleted, save the state to the config entry instead.
      SearchResultEntry configEntry = searchConfigEntry();
      if (configEntry != null)
      {
        DN configDN = configEntry.getDN();
        result = runUpdateStateEntry(configDN);
      }
    }
    return result;
  }

  /**
   * Run a modify operation to update the entry whose DN is given as
   * a parameter with the serverState information.
   *
   * @param serverStateEntryDN The DN of the entry to be updated.
   *
   * @return A ResultCode indicating if the operation was successful.
   */
  private ResultCode runUpdateStateEntry(DN serverStateEntryDN)
  {
    ArrayList<ByteString> values = state.toASN1ArrayList();

    LDAPAttribute attr =
      new LDAPAttribute(REPLICATION_STATE, values);
    LDAPModification mod = new LDAPModification(ModificationType.REPLACE, attr);
    ArrayList<RawModification> mods = new ArrayList<RawModification>(1);
    mods.add(mod);

    ModifyOperationBasis op =
      new ModifyOperationBasis(conn, InternalClientConnection.nextOperationID(),
          InternalClientConnection.nextMessageID(),
          new ArrayList<Control>(0),
          ByteString.valueOf(serverStateEntryDN.toString()),
          mods);
    op.setInternalOperation(true);
    op.setSynchronizationOperation(true);
    op.setDontSynchronize(true);
    op.run();
    if (op.getResultCode() != ResultCode.SUCCESS)
    {
      Message message = DEBUG_ERROR_UPDATING_RUV.get(
              op.getResultCode().getResultCodeName().toString(),
              op.toString(),
              op.getErrorMessage().toString(),
              baseDn.toString());
      logError(message);
    }
    return op.getResultCode();
  }

  /**
   * Empty the ServerState.
   * After this call the Server State will be in the same state
   * as if it was just created.
   */
  public void clearInMemory()
  {
    state.clear();
    state.setSaved(false);
  }

  /**
   * Empty the ServerState.
   * After this call the Server State will be in the same state
   * as if it was just created.
   */
  public void clear()
  {
    clearInMemory();
    save();
  }

  /**
   * The ServerState is saved to the database periodically,
   * therefore in case of crash it is possible that is does not contain
   * the latest changes that have been processed and saved to the
   * database.
   * In order to make sure that we don't loose them, search all the entries
   * that have been updated after this entry.
   * This is done by using the HistoricalCsnOrderingMatchingRule
   * and an ordering index for historical attribute
   */
  public final void checkAndUpdateServerState() {
    Message message;
    InternalSearchOperation op;
    CSN serverStateMaxCsn;
    CSN dbMaxCsn;
    final AttributeType histType = DirectoryServer.getAttributeType(
          EntryHistorical.HISTORICAL_ATTRIBUTE_NAME);

    // Retrieves the entries that have changed since the
    // maxCsn stored in the serverState
    synchronized (this)
    {
      serverStateMaxCsn = state.getCSN(serverId);

      if (serverStateMaxCsn == null)
        return;

      try {
        op = LDAPReplicationDomain.searchForChangedEntries(baseDn,
            serverStateMaxCsn, null);
      }
      catch (Exception  e)
      {
        return;
      }
      if (op.getResultCode() != ResultCode.SUCCESS)
      {
        // An error happened trying to search for the updates
        // Log an error
        message = ERR_CANNOT_RECOVER_CHANGES.get(
            baseDn.toNormalizedString());
        logError(message);
      }
      else
      {
        dbMaxCsn = serverStateMaxCsn;
        for (SearchResultEntry resEntry : op.getSearchEntries())
        {
          for (AttributeValue attrValue :
                    resEntry.getAttribute(histType).get(0))
          {
            HistoricalAttributeValue histVal =
                new HistoricalAttributeValue(attrValue.toString());
            CSN csn = histVal.getCSN();
            if (csn != null && csn.getServerId() == serverId)
            {
              // compare the csn regarding the maxCsn we know and
              // store the biggest
              if (CSN.compare(dbMaxCsn, csn) < 0)
              {
                dbMaxCsn = csn;
              }
            }
          }
        }

        if (CSN.compare(dbMaxCsn, serverStateMaxCsn) > 0)
        {
          // Update the serverState with the new maxCsn
          // present in the database
          this.update(dbMaxCsn);
          message = NOTE_SERVER_STATE_RECOVERY.get(
              baseDn.toNormalizedString(), dbMaxCsn.toString());
          logError(message);
        }
      }
    }
  }

  /**
   * Get the largest CSN seen for a given LDAP server ID.
   *
   * @param serverId
   *          The serverId
   * @return The largest CSN seen
   */
  public CSN getMaxCSN(int serverId)
  {
    return state.getCSN(serverId);
  }
}