/*
 * 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.iotdb.consensus.ratis;

import org.apache.iotdb.consensus.IStateMachine;
import org.apache.iotdb.consensus.ratis.utils.Utils;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.ratis.protocol.RaftGroupId;
import org.apache.ratis.server.protocol.TermIndex;
import org.apache.ratis.server.storage.FileInfo;
import org.apache.ratis.server.storage.RaftStorage;
import org.apache.ratis.statemachine.SnapshotInfo;
import org.apache.ratis.statemachine.SnapshotRetentionPolicy;
import org.apache.ratis.statemachine.StateMachineStorage;
import org.apache.ratis.statemachine.impl.FileListSnapshotInfo;
import org.apache.ratis.util.FileUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.IOException;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class SnapshotStorage implements StateMachineStorage {
  private final Logger logger = LoggerFactory.getLogger(SnapshotStorage.class);
  private final IStateMachine applicationStateMachine;

  private static final String TMP_PREFIX = ".tmp.";
  private File stateMachineDir;
  private final RaftGroupId groupId;
  private final ReentrantReadWriteLock snapshotCacheGuard = new ReentrantReadWriteLock();
  private SnapshotInfo currentSnapshot = null;

  public SnapshotStorage(IStateMachine applicationStateMachine, RaftGroupId groupId) {
    this.applicationStateMachine = applicationStateMachine;
    this.groupId = groupId;
  }

  @Override
  public void init(RaftStorage raftStorage) throws IOException {
    this.stateMachineDir =
        Optional.ofNullable(getSnapshotDir())
            .orElse(raftStorage.getStorageDir().getStateMachineDir());

    if (!stateMachineDir.exists()) {
      FileUtils.createDirectories(stateMachineDir);
    }
    updateSnapshotCache();
  }

  @Override
  public SnapshotInfo getLatestSnapshot() {
    snapshotCacheGuard.readLock().lock();
    try {
      return currentSnapshot;
    } finally {
      snapshotCacheGuard.readLock().unlock();
    }
  }

  @Override
  public void format() throws IOException {
    // Empty method, since it is not needed now
  }

  @Override
  public void cleanupOldSnapshots(SnapshotRetentionPolicy snapshotRetentionPolicy)
      throws IOException {
    final Path[] sortedSnapshotDirs = getSortedSnapshotDirPaths();
    if (ArrayUtils.isEmpty(sortedSnapshotDirs)) {
      return;
    }

    final int cleanIndex =
        Math.max(0, sortedSnapshotDirs.length - snapshotRetentionPolicy.getNumSnapshotsRetained());
    for (int i = 0; i < cleanIndex; i++) {
      FileUtils.deleteFully(sortedSnapshotDirs[i]);
    }
  }

  @Override
  public File getSnapshotDir() {
    return applicationStateMachine.getSnapshotRoot();
  }

  @Override
  public File getTmpDir() {
    return getSnapshotDir() == null
        ? null
        : new File(getSnapshotDir().getParentFile(), TMP_PREFIX + groupId.toString());
  }

  private Path[] getSortedSnapshotDirPaths() {
    ArrayList<Path> snapshotPaths = new ArrayList<>();
    try (DirectoryStream<Path> stream = Files.newDirectoryStream(getStateMachineDir().toPath())) {
      for (Path path : stream) {
        if (path.toFile().isDirectory() && !path.toFile().getName().startsWith(TMP_PREFIX)) {
          snapshotPaths.add(path);
        }
      }
    } catch (IOException exception) {
      logger.warn("cannot construct snapshot directory stream ", exception);
      return null;
    }

    Path[] pathArray = snapshotPaths.toArray(new Path[0]);
    Arrays.sort(
        pathArray,
        (o1, o2) -> {
          String index1 = o1.toFile().getName().split("_")[1];
          String index2 = o2.toFile().getName().split("_")[1];
          return Long.compare(Long.parseLong(index1), Long.parseLong(index2));
        });
    return pathArray;
  }

  public File findLatestSnapshotDir() {
    Path[] snapshots = getSortedSnapshotDirPaths();
    if (snapshots == null || snapshots.length == 0) {
      return null;
    }

    return snapshots[snapshots.length - 1].toFile();
  }

  SnapshotInfo findLatestSnapshot() {
    File latestSnapshotDir = findLatestSnapshotDir();
    if (latestSnapshotDir == null) {
      return null;
    }
    TermIndex snapshotTermIndex = Utils.getTermIndexFromDir(latestSnapshotDir);

    List<Path> actualSnapshotFiles = applicationStateMachine.getSnapshotFiles(latestSnapshotDir);
    if (actualSnapshotFiles == null) {
      return null;
    }

    List<FileInfo> fileInfos = new ArrayList<>();
    for (Path file : actualSnapshotFiles) {
      if (file.endsWith(".md5")) {
        continue;
      }
      FileInfo fileInfo = null;
      try {
        if (getSnapshotDir() == null) {
          // for regions that place the snapshot in default sm folder, use relative path
          fileInfo = new FileInfo(file, null);
        } else {
          // for regions that have a separate snapshot installation path, use absolute path
          fileInfo = new FileInfo(file.toRealPath(), null);
        }
      } catch (IOException e) {
        logger.warn("{} cannot resolve real path of {} due to ", this, file, e);
        return null;
      }
      fileInfos.add(fileInfo);
    }

    return new FileListSnapshotInfo(
        fileInfos, snapshotTermIndex.getTerm(), snapshotTermIndex.getIndex());
  }

  /*
  Snapshot cache will be updated upon:
  1. takeSnapshot, when RaftServer takes a new snapshot
  2. loadSnapshot, when RaftServer is asked to load a snapshot. loadSnapshot will be called when
  (1) initialize, RaftServer first starts
  (2) reinitialize, RaftServer resumes from pause. Leader will install a snapshot during pause.
   */
  void updateSnapshotCache() {
    snapshotCacheGuard.writeLock().lock();
    try {
      currentSnapshot = findLatestSnapshot();
    } finally {
      snapshotCacheGuard.writeLock().unlock();
    }
  }

  File getStateMachineDir() {
    return stateMachineDir;
  }

  File getSnapshotDir(String snapshotMetadata) {
    return new File(getStateMachineDir().getAbsolutePath() + File.separator + snapshotMetadata);
  }

  File getSnapshotTmpDir(String snapshotMetadata) {
    return new File(
        getStateMachineDir().getAbsolutePath() + File.separator + TMP_PREFIX + snapshotMetadata);
  }

  String getSnapshotTmpId(String snapshotMetadata) {
    return TMP_PREFIX + snapshotMetadata;
  }
}
