/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.master.assignment;

import com.google.errorprone.annotations.RestrictedApi;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.LongConsumer;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.RegionInfo;
import org.apache.hadoop.hbase.client.TableState;
import org.apache.hadoop.hbase.master.RegionState;
import org.apache.hadoop.hbase.master.TableStateManager;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import org.apache.hadoop.hbase.util.Pair;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Tracks regions that are currently in transition (RIT) - those not yet in their terminal state.
 */
@InterfaceAudience.Private
public class RegionInTransitionTracker {
  private static final Logger LOG = LoggerFactory.getLogger(RegionInTransitionTracker.class);

  private static final List<RegionState.State> DISABLE_TABLE_REGION_STATE =
    List.of(RegionState.State.OFFLINE, RegionState.State.CLOSED);

  private static final List<RegionState.State> ENABLE_TABLE_REGION_STATE =
    List.of(RegionState.State.OPEN);

  // DO NOT USE containsKey()/remove() on regionInTransition with a RegionInfo instance whose
  // offline flag differs from the one stored as the key: RegionInfo#equals and #hashCode both
  // include the offline flag, so such a lookup misses even when it refers to the same region.
  // Offline value changes with splitting.
  private final ConcurrentHashMap<RegionInfo, Pair<RegionStateNode, Long>> regionInTransition =
    new ConcurrentHashMap<>();

  private final LongConsumer ritDurationConsumer;
  private TableStateManager tableStateManager;

  public RegionInTransitionTracker(LongConsumer ritDurationConsumer) {
    this.ritDurationConsumer = Objects.requireNonNull(ritDurationConsumer);
  }

  @RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  boolean isRegionInTransition(final RegionInfo regionInfo) {
    return regionInTransition.containsKey(regionInfo);
  }

  /**
   * Handles a region whose hosting RegionServer has crashed. When a RegionServer fails, all regions
   * it was hosting are automatically added to the RIT list since they need to be reassigned to
   * other servers.
   * @param regionStateNode the region whose hosting server crashed
   * @param crashTime       the RIT start time to use when the region is not already in transition
   *                        (an existing entry keeps its earlier start). Passed explicitly rather
   *                        than read from {@link RegionStateNode#getLastUpdate()}, which a stale
   *                        procedure can mask. A non-positive value falls back to the node's last
   *                        update.
   */
  public void regionCrashed(RegionStateNode regionStateNode, long crashTime) {
    if (isReplica(regionStateNode)) {
      return;
    }

    long startTime = crashTime > 0 ? crashTime : regionStateNode.getLastUpdate();
    if (addRegionInTransition(regionStateNode, startTime)) {
      LOG.debug("{} added to RIT list because hosting region server is crashed ",
        regionStateNode.getRegionInfo().getEncodedName());
    }
  }

  /**
   * Processes a region state change and updates the RIT tracking accordingly. This is the core
   * method that determines whether a region should be added to or removed from the RIT list based
   * on its current state and the table's enabled/disabled status. This method should be called
   * whenever a region state changes get stored to hbase:meta Note: Only default replicas (replica
   * ID 0) are tracked. Read replicas are ignored.
   * @param regionStateNode the region state node with the current state information
   */
  public void handleRegionStateNodeOperation(RegionStateNode regionStateNode) {
    // only consider default replica for availability
    if (isReplica(regionStateNode)) {
      return;
    }

    RegionState.State currentState = regionStateNode.getState();
    boolean tableEnabled = isTableEnabled(regionStateNode.getTable());
    List<RegionState.State> terminalStates =
      tableEnabled ? ENABLE_TABLE_REGION_STATE : DISABLE_TABLE_REGION_STATE;

    // if region is merged or split it should not be in RIT list
    if (AssignmentManagerUtil.isSplitOrMerged(regionStateNode)) {
      if (removeRegionInTransition(regionStateNode.getRegionInfo())) {
        LOG.debug("Removed {} from RIT list as it is split or merged",
          regionStateNode.getRegionInfo().getEncodedName());
      }
    } else if (!terminalStates.contains(currentState)) {
      if (addRegionInTransition(regionStateNode)) {
        LOG.debug("{} added to RIT list because it is in-between state, region state : {} ",
          regionStateNode.getRegionInfo().getEncodedName(), currentState);
      }
    } else {
      if (removeRegionInTransition(regionStateNode.getRegionInfo())) {
        LOG.debug("Removed {} from RIT list as reached to terminal state {}",
          regionStateNode.getRegionInfo().getEncodedName(), currentState);
      }
    }
  }

  private boolean isTableEnabled(TableName tableName) {
    if (tableStateManager != null) {
      return tableStateManager.isTableState(tableName, TableState.State.ENABLED,
        TableState.State.ENABLING);
    }
    // AssignmentManager calls setTableStateManager once hbase:meta is confirmed online, if it is
    // still null it means confirmation is still pending. One should not access TableStateManger
    // till the time.
    assert TableName.isMetaTableName(tableName);
    return true;
  }

  /**
   * Handles the deletion of a region by removing it from RIT tracking. This is called when a region
   * is permanently removed from the cluster, typically after a successful merge operation where the
   * parent regions are cleaned up. During table deletion, table should be already disabled and all
   * the region are already OFFLINE
   * @param regionInfo the region being deleted
   */
  public void handleRegionDelete(RegionInfo regionInfo) {
    removeRegionInTransition(regionInfo);
  }

  private boolean addRegionInTransition(final RegionStateNode regionStateNode) {
    return addRegionInTransition(regionStateNode, regionStateNode.getLastUpdate());
  }

  private boolean addRegionInTransition(final RegionStateNode regionStateNode, long startTime) {
    if (startTime <= 0) {
      startTime = EnvironmentEdgeManager.currentTime();
    }
    return regionInTransition.putIfAbsent(regionStateNode.getRegionInfo(),
      Pair.newPair(regionStateNode, startTime)) == null;
  }

  private boolean removeRegionInTransition(final RegionInfo regionInfo) {
    Pair<RegionStateNode, Long> removed = regionInTransition.remove(regionInfo);
    if (removed != null) {
      long duration = EnvironmentEdgeManager.currentTime() - removed.getSecond();
      if (duration >= 0) {
        ritDurationConsumer.accept(duration);
      }
    }
    return removed != null;
  }

  public void stop() {
    regionInTransition.clear();
  }

  public boolean hasRegionsInTransition() {
    return !regionInTransition.isEmpty();
  }

  public int getRegionsInTransitionCount() {
    return regionInTransition.size();
  }

  public List<RegionStateNode> getRegionsInTransition() {
    List<RegionStateNode> regions = new ArrayList<>(regionInTransition.size());
    for (Pair<RegionStateNode, Long> entry : regionInTransition.values()) {
      regions.add(entry.getFirst());
    }
    return regions;
  }

  public void setTableStateManager(TableStateManager tableStateManager) {
    this.tableStateManager = tableStateManager;
  }

  private static boolean isReplica(RegionStateNode regionStateNode) {
    return regionStateNode.getRegionInfo().getReplicaId() != RegionInfo.DEFAULT_REPLICA_ID;
  }
}