/**
 * 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.hdfs.server.federation.store.driver.impl;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.hadoop.classification.VisibleForTesting;
import org.apache.hadoop.hdfs.server.federation.router.RBFConfigKeys;
import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hadoop.thirdparty.com.google.common.io.Files;

/**
 * StateStoreDriver implementation based on a local file.
 */
public class StateStoreFileImpl extends StateStoreFileBaseImpl {

  private static final Logger LOG =
      LoggerFactory.getLogger(StateStoreFileImpl.class);

  /** Configuration keys. */
  public static final String FEDERATION_STORE_FILE_DIRECTORY =
      RBFConfigKeys.FEDERATION_STORE_PREFIX + "driver.file.directory";

  /** Root directory for the state store. */
  private String rootDirectory;


  @Override
  protected boolean exists(String path) {
    File test = new File(path);
    return test.exists();
  }

  @Override
  protected boolean mkdir(String path) {
    File dir = new File(path);
    return dir.mkdirs();
  }

  @Override
  protected boolean rename(String src, String dst) {
    try {
      Files.move(new File(src), new File(dst));
      return true;
    } catch (IOException e) {
      LOG.error("Cannot rename {} to {}", src, dst, e);
      return false;
    }
  }

  @Override
  protected boolean remove(String path) {
    File file = new File(path);
    return file.delete();
  }

  @Override
  protected String getRootDir() {
    if (this.rootDirectory == null) {
      String dir = getConf().get(FEDERATION_STORE_FILE_DIRECTORY);
      if (dir == null) {
        File tempDirBase =
            new File(System.getProperty("java.io.tmpdir"));
        File tempDir = null;
        try {
          tempDir = java.nio.file.Files.createTempDirectory(
              tempDirBase.toPath(), System.currentTimeMillis() + "-").toFile();
        } catch (IOException e) {
          // fallback to the base upon exception.
          LOG.debug("Unable to create a temporary directory. Fall back to " +
              " the default system temp directory {}", tempDirBase, e);
          tempDir = tempDirBase;
        }
        dir = tempDir.getAbsolutePath();
        LOG.warn("The root directory is not available, using {}", dir);
      }
      this.rootDirectory = dir;
    }
    return this.rootDirectory;
  }

  @Override
  protected int getConcurrentFilesAccessNumThreads() {
    return getConf().getInt(RBFConfigKeys.FEDERATION_STORE_FILE_ASYNC_THREADS,
        RBFConfigKeys.FEDERATION_STORE_FILE_ASYNC_THREADS_DEFAULT);
  }

  @Override
  protected <T extends BaseRecord> BufferedReader getReader(String filename) {
    BufferedReader reader = null;
    try {
      LOG.debug("Loading file: {}", filename);
      File file = new File(filename);
      FileInputStream fis = new FileInputStream(file);
      InputStreamReader isr =
          new InputStreamReader(fis, StandardCharsets.UTF_8);
      reader = new BufferedReader(isr);
    } catch (Exception ex) {
      LOG.error("Cannot open read stream for record {}", filename, ex);
    }
    return reader;
  }

  @Override
  @VisibleForTesting
  public <T extends BaseRecord> BufferedWriter getWriter(String filename) {
    BufferedWriter writer = null;
    try {
      LOG.debug("Writing file: {}", filename);
      File file = new File(filename);
      FileOutputStream fos = new FileOutputStream(file, false);
      OutputStreamWriter osw =
          new OutputStreamWriter(fos, StandardCharsets.UTF_8);
      writer = new BufferedWriter(osw);
    } catch (IOException e) {
      LOG.error("Cannot open write stream for record {}", filename, e);
    }
    return writer;
  }

  @Override
  public void close() throws Exception {
    super.close();
    setInitialized(false);
  }

  @Override
  protected List<String> getChildren(String path) {
    File dir = new File(path);
    File[] files = dir.listFiles();
    if (ArrayUtils.isNotEmpty(files)) {
      List<String> ret = new ArrayList<>(files.length);
      for (File file : files) {
        String filename = file.getName();
        ret.add(filename);
      }
      return ret;
    }
    return Collections.emptyList();
  }
}